Application of laser ablation inductively coupled plasma (dynamic reaction cell) mass spectrometry...
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Chemical Geology 21
The application of laser ablation-inductively coupled plasma-mass
spectrometry to in situ UndashPb zircon geochronology
Simon E Jacksona Norman J Pearsona William L Griffinab Elena A Belousovaa
aGEMOC National Key Centre Department of Earth and Planetary Sciences Macquarie University North Ryde NSW 2109 AustraliabCSIRO Exploration and Mining North Ryde NSW 2113 Australia
Received 21 May 2003 accepted 7 June 2004
Abstract
This paper reports new developments in in situ UndashPb zircon geochronology using 266 and 213 nm laser ablation-inductively
coupled plasma-mass spectrometry (LA-ICP-MS)
Standard spot ablation (spot diameters 40ndash80 Am) was employed with no sampling strategies employed specifically to
minimise elemental fractionation Instead He ablation gas and carefully replicated ablation conditions were employed to
maintain constant ablation-related elemental fractionation of Pb and U between analyses Combining these strategies with
calibration on a new zircon standard (GJ-1) allows elemental fractionation and instrumental mass bias to be corrected efficiently
and accurate 206Pb238U and 207Pb235U ratios to be measured with short-term precision (2 rsd) of 19 and 30
respectively
Long-term precision (2 rsd) of the technique (266 nm ablation) based on 355 analyses of the 91500 zircon (1065 Ma)
standard over more than a year was 38 40 and 14 for the 206Pb238U 207Pb235U and 207Pb206Pb ratios respectively
Long-term precision (2 rsd) for the 206Pb238U 207Pb235U and 207Pb206Pb ratios of the Mud Tank zircon (732 Ma) was 39
41 and 17 respectively (359 analyses) Selective integration of time-resolved signals was used to minimise the effect of Pb
loss and common Pb enrichments on the measured ages The precision and accuracy of our data compare very favourably with
those obtained using more involved procedures to correct or minimise ablation- and ICP-MS-induced biases
213 nm laser ablation produced comparable precision to 266 nm ablation using generally smaller spot sizes (40ndash50 vs
60ndash80 Am) and offered significant advantages in terms of ablation duration and stability particularly for small zircons
(b60 Am) For the 91500 zircon but not the Mud Tank zircon 213 nm ablation also produced significantly older and more
accurate PbU ages This suggests that shorter wavelength ablation may have reduced a matrix-dependent elemental
fractionation difference between sample and standard
The accuracy and precision of the technique for young zircons are demonstrated by analysis of three zircon populations
ranging in age from 417 to 7 Ma In each case the zircons have yielded concordant ages or common Pb discordia which give
concordia intercept ages that are in agreement with independently determined ages for the same samples Application of Terandash
0009-2541$ - s
doi101016jch
Correspon
E-mail addr
1 (2004) 47ndash69
ee front matter D 2004 Elsevier BV All rights reserved
emgeo200406017
ding author
ess sjacksonelsmqeduau (SE Jackson)
SE Jackson et al Chemical Geology 211 (2004) 47ndash6948
Wasserburg diagrams [Earth Planet Sci Lett 14 (1972) 281] was found to be the most useful approach to handling common Pb
contributions that were not removed by selective integration of signals
D 2004 Elsevier BV All rights reserved
Keywords Laser ablation-ICP-MS UndashPb geochronology Zircon Calibration
1 Introduction
The first demonstrations of the potential of LA-
ICP-MS to perform in situ 207Pb206Pb determinations
on zircon with sufficient precision to be a useful tool
for dating Proterozoic and older zircons took place in
the early 1990s (Fryer et al 1993 Feng et al 1993)
However it is only since the development of UV laser
ablation and high-sensitivity ICP-MS instrumentation
in the mid-1990s that the technique has been applied
widely to in situ zircon dating using the PbU decay
schemes (eg Hirata and Nesbitt 1995 Jackson et
al 1996 Fernandez-Suarez et al 1998 Horn et al
2000 Ketchum et al 2001 Li et al 2001 Kosler et
al 2002 Tiepolo et al 2003 Tiepolo 2003) The
measurement of 207Pb235U and 206Pb238U ratios
allows assessment of concordance and extraction of
a true age from zircon populations that have suffered
variable Pb loss from grains or parts thereof
The increasing use of LA-ICP-MS UndashPb dating
derives from the fact that it is the cheapest most
widely available and fastest technique for in situ UndashPb
dating While it is not as well suited as SIMS for
applications requiring high-resolution sampling (eg
dating complex zircons with small cores andor
overgrowths) it is extremely well suited to projects
needing large numbers of analyses (eg detrital
zircon studies) Despite increasing usage however
the LA-ICP-MS technique is not universally accepted
as a robust technique for zircon dating The most
frequently cited drawbacks of UndashPb dating using LA-
ICP-MS are as follows (1) fractionation of Pb relative
to U during the ablationtransport and ionisation
processes (eg Hirata and Nesbitt 1995 Fryer et
al 1995) and (2) difficulty in performing a useful
common Pb correction based on 204Pb due to the
overwhelming isobaric interference from Hg
It is clear that elemental fractionation during
ablation is related to differential volatilisation and
condensation processes but the there has been
considerable debate about the possible mechanisms
involved (see Jackson 2001 for a review) Possible
mechanisms that give rise to ablation time-dependent
elemental fractionation include the following (1)
dynamic differential volatilisationcondensation pro-
cesses within or close to an ablation pit related to
progressive defocusing of the laser as it penetrates
into the sample (Hirata and Nesbitt 1995) or to the
evolving aspect ratio of the pit (Eggins et al 1998
Mank and Mason 1999) (2) partitioning of elements
preferentially into a particulate (refractory elements)
or vapour phase (volatile elements) which are differ-
entially transported (Outridge et al 1997) and (3)
differential volatilisation of elements during incom-
plete vapourisation of particulates due to insufficient
residence time in the ICP (Guillong and Gunther
2002)
A wide variety of procedures has been invoked in
previous LA-ICP-MS UndashPb studies to minimise
andor correct for ablation-related elemental fractiona-
tion in addition to the inherent mass bias of the ICP-
MS instrument bActive focussingQ (raising the sample
stage during ablation to maintain constant laser focus
on the ablation surface) was used together with
standardisation on a NIST glass reference material
by Hirata and Nesbitt (1995) This method has not
been widely adopted because of the design limitations
of LA hardware and because it requires time-consum-
ing optimisation of the rate of sample height adjust-
ment for different ablation conditions
A more practical approach to preventing formation
of deep craters and maintaining constant focus
conditions is to use raster ablation in which the
sample is constantly moved laterally during ablation
(eg Li et al 2001 Horstwood et al 2001 Kosler et
al 2002) The main drawback of this method is that it
compromises the spatial resolution attainable (or
requires use of a very small beam which reduces
the ablation rate and thus the signalnoise ratio) Use
of an external standard or an alternate correction
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 49
procedure is still required to correct instrumental mass
bias
Several studies have made use of a bjet cellQ whichintroduces the carrier gas as a high-velocity jet
directly onto the ablation site (Jackson et al 1996
Horn et al 2000 Jackson 2001) to reduce fractio-
nation together with calibration against a zircon
standard (eg Fernandez-Suarez et al 1998
Ketchum et al 2001) While the jet cell can produce
a significant reduction in fractionation (ca 50)
maintaining precise alignment of the carrier gas jet
onto the ablation site is difficult and represents a
serious limitation to this cell design
Horn et al (2000) used an experimentally derived
mathematical procedure that relates fractionation to
spot geometry (at constant energy density) to correct
for ablation-related elemental fractionation together
with use of a Tl235U spike to correct for instrumental
mass bias This method requires elemental fractiona-
tion to be extremely reproducible from day to day It is
better suited to the flat energy profiles of excimer laser
systems (eg Horn et al 2000) than NdYAG
systems (Tiepolo et al 2003) for which the energy
distribution within the laser beam can vary signifi-
cantly depending upon laser tuning and operating
conditions
In this study we used a high-sensitivity quadrupole
ICP-MS coupled to a custom-built UV laser ablation
microprobe based on a frequency quadrupled NdYAG
laser (k=266 nm) Also evaluated was a commercial
frequency-quintupled (k=213 nm) laser ablation sys-
tem We describe and evaluate a simple technique that
employs spot ablations with no specific strategies to
minimise ablation-related elemental fractionation
Fractionation and instrumental mass bias are corrected
by direct calibration against a new zircon standard
analysed under carefully matched conditions using He
as the ablation gas to increase the reproducibility of the
PbU fractionation Time-resolved data acquisition is
employed to evaluate zircon homogeneity and to allow
selective integration of signals to minimise common
Pb contributions and Pb loss and thus to maximise
concordance TerandashWasserburg diagrams (Tera and
Wasserburg 1972) are also employed to assess and
correct for residual common Pb contributions These
procedures are evaluated using data for five zircons
ranging in age from 1065 to 7 Ma Two of these
zircons have been analysed more than 400 times over
more than a year by two instrument operators
allowing an exhaustive evaluation of the long-term
precision and accuracy of the technique
2 Analytical techniques
21 Sample preparation
All zircons were mounted in epoxy in 25-cm-
diameter circular grain mounts and polished until the
zircons were just revealed Images of the zircons were
obtained using the back-scatter electron (BSE) detector
on a Cameca SX50 electron microprobe The BSE
detector is a light-sensitive diode so the image
obtained of the internal structure of the zircon is a
combination of the variation in mean atomic number
(composition) as well as the cathodoluminescence
(CL) BSECL images were taken of all analysed
zircons to study the internal structure of the grains prior
to LA-ICP-MS analysis Grain mounts containing the
samples and standards were cleaned in 1 N nitric acid
immediately prior to analysis to remove surface Pb
contamination This removed the necessity for pre-
ablating the samples to remove surface contamination
22 Instrumentation
The laser ablation microprobe uses a focussed laser
beam to ablate a small amount of a sample contained
in a closed cell The ablated material is transported
from the cell in a carrier gas (Ar or He) to an ICP-MS
for isotopic quantification For the spot diameters
(mostly 50ndash80 Am) and ablation times (ca 60 s) used
in this study ablated masses of zircon were approx-
imately 500ndash1500 ng
Two laser ablation (LA) systems were used in this
study Most analyses were performed using a custom-
built UV LA sampler that has been described by
Norman et al (1996) The system incorporates a
frequency-quadrupled NdYAG laser (k=266 nm) and
beam delivery optics that attenuate the beam to the
required fluence and steer the beam down the photo-
tube of a petrographic microscope The microscope
incorporates specialised optics that focus the laser and
provide a high-quality image of the sample which
greatly facilitates locating sample sites in petrographic
mounts The sample mount and standardisation materi-
SE Jackson et al Chemical Geology 211 (2004) 47ndash6950
als were ablated in a sample cell approximately 8 cm in
diameter with a Teflon insert that holds up to four 25-
mm sample mounts A 05-mm restriction on the gas
inlet nozzle results in a jet-like flow across the samples
which results in amuchmore stable ablation signal than
a comparable cell without a restricted inlet nozzle The
ablated sample was transferred to the ICP-MS through
3 mm id PVC tubing that was cleaned by soaking in
02 N nitric acid prior to use and replaced on a monthly
basis
Ablation was performed in a He carrier gas (except
where noted otherwise) as first described by Eggins et
al (1998) The He carrier exiting the sample cell was
combined with Ar in a 30 cm3 mixing chamber prior to
entering the ICP The gas plumbing configuration
includes a two-way valve on the Ar line so that after
each ablation the user may switch the Ar to combine
with the He before entering the sample cell The ArndashHe
mixture flushes ablated particles from the cell much
faster than He alone resulting in a more rapid return of
signals to background levels and increased sample
throughput Operating conditions of the LA systems
are reported in Table 1
Constant LA operating conditions were maintained
throughout each analytical brunQ (18ndash22 analyses)
because elemental fractionation is extremely sensitive
to laser pulse energy and focus Moderate- to high-
power frequency-quadrupled NdYAG lasers require a
significant period (minutes) to attain stable output after
the initiation of lasing due largely to the thermal-
equilibration time of the temperature-sensitive 4th
harmonic crystal Constant ablation conditions were
achieved by leaving the laser firing continuously
throughout a run and initiating and terminating ablation
by unblocking and blocking the beam path
All analyses were performed with the laser focused
above the sample (typically ca 150ndash250 Am) This was
found to be a more robust method than bactivefocusingQ (Hirata and Nesbitt 1995) for reducing the
relative change in focus of the laser beam as it
penetrates into the sample since it does not require
optimisation of the vertical translation rate of
the stage for different laser operating conditions
(Jackson 2001) While greater defocusing reduces
ablation time-dependent fractionation of Pb and U it
increases the ablation spot size The degree of
defocusing was therefore set to give the maximum
crater diameter possible for a set of zircons The
266 nm laser system was used mostly for large zircons
where large spot sizes (60ndash80 Am in diameter) were
appropriate
Also evaluated in this study was a commercial
LUV213 laser ablation system (k=213 nm) (New
Wave ResearchMerchantek) The LUV213 was used
primarily for analysis of small zircons (b60 Am)
which can be difficult to ablate controllably at 266 nm
due to the high transmittance of the laser beam
through the grain into the underlying epoxy mounting
medium Due to the greater absorption of the 213 nm
laser beam the incidence of catastrophic ablation was
significantly reduced Most of the 213 nm laser data
presented here are for smaller spots (40ndash50 Am) than
produced with the 266 nm laser
The LUV213 was used with an in-house built
sample cell similar to that used on the 266 nm laser
except for a smaller cell diameter (ca 6 cm)
necessitated by space limitations Much lower beam
energies enter the harmonic generators in this system
compared to the 266 nm laser sampler due to the
lower output energy of the laser and the optical
configuration of the system Thus the 213 nm laser
sampler does not require a significant stabilisation
period after initiating ablation and no pre-ablation
warm up was used
The ICP-MS used was an Agilent 4500 a high-
sensitivity quadrupole ICP-MS that provides a sensi-
tivity of in excess of 200 million counts per second
(cps)ppm for mono-isotopic heavy elements (atomic
mass N85) in standard solutionmode Current detection
limits for these elements using laser ablation sampling
are typically b10 ppb for a 60-s analysis at 40ndash50 Amsampling resolution ICP-MS operating conditions
were generally optimised using continuous ablation
of our in-house GJ-1 zircon standard to provide
maximum sensitivity for the high masses (PbndashU) while
maintaining low oxide formation (ThO+Th+b15)
Few analyses give signals in excess of 2000000 cps
and thus all readings were made in pulse counting
mode employing a dead-time correction applied
automatically by the ICP-MS operating system
Instrumental background was established by the
standard procedure of measurement of a bgas blankQie analysis of the carrier gas with no laser ablation
(eg Hirata andNesbitt 1995 Fernandez-Suarez et al
1998 Horn et al 2000 Kosler et al 2002 Tiepolo et
al 2003 Tiepolo 2003) Adoption of this procedure
Table 1
LA-ICP-MS operating conditions and data acquisition parameters
ICP-MS
Model Agilent 4500
Forward power 1350 W
Gas flows
Plasma (Ar) 16 lmin
Auxiliary (Ar) 1 lmin
Carrier (He) 09ndash12 lmin
Make-up (Ar) 09ndash12 lmin
Shield torch Used for most
analyses
Expansion
chamber
pressure
350ndash360 Paa
LA Custom system LUV 213
Wavelength 266 nm 213 nm
Repetition rate 5 and 10 Hz 5 and 10 Hz
Pre-ablation laser
warm up
Laser fired
continuously
None
Pulse duration
(FWHM)
9 ns 5 ns
Apertured beam
diameteriris
setting
4 mm 15
Beam
expander setting
na 0
Focusing objective 10 fl = 20 mm 5 fl = 40 mm
Degree of
defocusing
150ndash250 Am(above sample)
Not known
Spot size 60ndash80 Am 40ndash50 AmIncident
pulse energy
ca 035 ca 01 mJ
Energy density
on sample
ca 12 J cm2 ca 8 J cm2
Data acquisition parameters
Data acquisition
protocol
Time-resolved analysis
Scanning mode Peak hopping 1 point
per peak
Detector mode Pulse counting
dead-time
correction applied
Isotopes
determined
206Pb 207Pb 208Pb232Th 238U
Dwell time
per isotope
15 30 10 10 15 ms
respectively
Quadrupole
settling time
ca 2 ms
Timescan ca 89 ms
Data acquisition (s) 180 s (60 s gas blank
up to 120 s ablation)
Table 1 (continued)
Samples and standrds
Mounts 25 mm diameter polished
grain mounts
Standard Gem zircon bGJ-1Q 609 Maa Pirani vacuum gauge may not be calibrated accurately for
ArHe mixtures
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 51
followed experiments to determine whether an
bablation blankQ (a blank measured while ablating)
might be a more appropriate measure of the true
background An ablation blank would take into account
any contribution to background derived from particles
released from the sample cell or transfer tubing wall by
the shock wave induced by laser ablation However
multiple ablations of high-purity synthetic fused silica
produced Pb Th and U count rates that were higher
than the gas background by an amount (median values
of b5 cps on 206Pb 207Pb and 238U b10 cps on 208Pb
and 232Th) that could reasonably have been derived
from Pb Th and U in the silica and in any case would
not significantly affect the vast majority of UndashPb
analyses (see the discussion of potential effect on208Pb232Th determination in Section 24)
For UndashPb work low gas background signals for Pb
are essential Low Pb gas backgrounds were achieved
by (1) careful attention to cleanliness of the LA system
(acid cleaning sample cell and inserts samples
delivery tubing) (2) dedicating the ICP-MS to laser
ablation analysis since analysis of solutions invariably
has a detrimental and long-term effect on Pb back-
grounds and (3) use of a liquid rather than a
compressed Ar supply Under these conditions typical
gas blank 208Pb signals of ca 30ndash40 cps were achieved
routinely Backgrounds were b10 cps for the other
elements of interest except Hg (ca 300 cps on 202Hg)
23 Data acquisition
Data acquisition parameters are listed in Table 1
Data were acquired on five isotopes using the
instrumentrsquos time-resolved analysis data acquisition
software The time-resolved analysis software reports
signal intensity data (cps) for each mass sweep
performed by the mass spectrometer This data
acquisition protocol allows acquisition of signals as a
function of time (ablation depth) and subsequent
recognition of isotopic heterogeneity within the abla-
tion volume (eg zones of Pb loss or common Pb
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6948
Wasserburg diagrams [Earth Planet Sci Lett 14 (1972) 281] was found to be the most useful approach to handling common Pb
contributions that were not removed by selective integration of signals
D 2004 Elsevier BV All rights reserved
Keywords Laser ablation-ICP-MS UndashPb geochronology Zircon Calibration
1 Introduction
The first demonstrations of the potential of LA-
ICP-MS to perform in situ 207Pb206Pb determinations
on zircon with sufficient precision to be a useful tool
for dating Proterozoic and older zircons took place in
the early 1990s (Fryer et al 1993 Feng et al 1993)
However it is only since the development of UV laser
ablation and high-sensitivity ICP-MS instrumentation
in the mid-1990s that the technique has been applied
widely to in situ zircon dating using the PbU decay
schemes (eg Hirata and Nesbitt 1995 Jackson et
al 1996 Fernandez-Suarez et al 1998 Horn et al
2000 Ketchum et al 2001 Li et al 2001 Kosler et
al 2002 Tiepolo et al 2003 Tiepolo 2003) The
measurement of 207Pb235U and 206Pb238U ratios
allows assessment of concordance and extraction of
a true age from zircon populations that have suffered
variable Pb loss from grains or parts thereof
The increasing use of LA-ICP-MS UndashPb dating
derives from the fact that it is the cheapest most
widely available and fastest technique for in situ UndashPb
dating While it is not as well suited as SIMS for
applications requiring high-resolution sampling (eg
dating complex zircons with small cores andor
overgrowths) it is extremely well suited to projects
needing large numbers of analyses (eg detrital
zircon studies) Despite increasing usage however
the LA-ICP-MS technique is not universally accepted
as a robust technique for zircon dating The most
frequently cited drawbacks of UndashPb dating using LA-
ICP-MS are as follows (1) fractionation of Pb relative
to U during the ablationtransport and ionisation
processes (eg Hirata and Nesbitt 1995 Fryer et
al 1995) and (2) difficulty in performing a useful
common Pb correction based on 204Pb due to the
overwhelming isobaric interference from Hg
It is clear that elemental fractionation during
ablation is related to differential volatilisation and
condensation processes but the there has been
considerable debate about the possible mechanisms
involved (see Jackson 2001 for a review) Possible
mechanisms that give rise to ablation time-dependent
elemental fractionation include the following (1)
dynamic differential volatilisationcondensation pro-
cesses within or close to an ablation pit related to
progressive defocusing of the laser as it penetrates
into the sample (Hirata and Nesbitt 1995) or to the
evolving aspect ratio of the pit (Eggins et al 1998
Mank and Mason 1999) (2) partitioning of elements
preferentially into a particulate (refractory elements)
or vapour phase (volatile elements) which are differ-
entially transported (Outridge et al 1997) and (3)
differential volatilisation of elements during incom-
plete vapourisation of particulates due to insufficient
residence time in the ICP (Guillong and Gunther
2002)
A wide variety of procedures has been invoked in
previous LA-ICP-MS UndashPb studies to minimise
andor correct for ablation-related elemental fractiona-
tion in addition to the inherent mass bias of the ICP-
MS instrument bActive focussingQ (raising the sample
stage during ablation to maintain constant laser focus
on the ablation surface) was used together with
standardisation on a NIST glass reference material
by Hirata and Nesbitt (1995) This method has not
been widely adopted because of the design limitations
of LA hardware and because it requires time-consum-
ing optimisation of the rate of sample height adjust-
ment for different ablation conditions
A more practical approach to preventing formation
of deep craters and maintaining constant focus
conditions is to use raster ablation in which the
sample is constantly moved laterally during ablation
(eg Li et al 2001 Horstwood et al 2001 Kosler et
al 2002) The main drawback of this method is that it
compromises the spatial resolution attainable (or
requires use of a very small beam which reduces
the ablation rate and thus the signalnoise ratio) Use
of an external standard or an alternate correction
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 49
procedure is still required to correct instrumental mass
bias
Several studies have made use of a bjet cellQ whichintroduces the carrier gas as a high-velocity jet
directly onto the ablation site (Jackson et al 1996
Horn et al 2000 Jackson 2001) to reduce fractio-
nation together with calibration against a zircon
standard (eg Fernandez-Suarez et al 1998
Ketchum et al 2001) While the jet cell can produce
a significant reduction in fractionation (ca 50)
maintaining precise alignment of the carrier gas jet
onto the ablation site is difficult and represents a
serious limitation to this cell design
Horn et al (2000) used an experimentally derived
mathematical procedure that relates fractionation to
spot geometry (at constant energy density) to correct
for ablation-related elemental fractionation together
with use of a Tl235U spike to correct for instrumental
mass bias This method requires elemental fractiona-
tion to be extremely reproducible from day to day It is
better suited to the flat energy profiles of excimer laser
systems (eg Horn et al 2000) than NdYAG
systems (Tiepolo et al 2003) for which the energy
distribution within the laser beam can vary signifi-
cantly depending upon laser tuning and operating
conditions
In this study we used a high-sensitivity quadrupole
ICP-MS coupled to a custom-built UV laser ablation
microprobe based on a frequency quadrupled NdYAG
laser (k=266 nm) Also evaluated was a commercial
frequency-quintupled (k=213 nm) laser ablation sys-
tem We describe and evaluate a simple technique that
employs spot ablations with no specific strategies to
minimise ablation-related elemental fractionation
Fractionation and instrumental mass bias are corrected
by direct calibration against a new zircon standard
analysed under carefully matched conditions using He
as the ablation gas to increase the reproducibility of the
PbU fractionation Time-resolved data acquisition is
employed to evaluate zircon homogeneity and to allow
selective integration of signals to minimise common
Pb contributions and Pb loss and thus to maximise
concordance TerandashWasserburg diagrams (Tera and
Wasserburg 1972) are also employed to assess and
correct for residual common Pb contributions These
procedures are evaluated using data for five zircons
ranging in age from 1065 to 7 Ma Two of these
zircons have been analysed more than 400 times over
more than a year by two instrument operators
allowing an exhaustive evaluation of the long-term
precision and accuracy of the technique
2 Analytical techniques
21 Sample preparation
All zircons were mounted in epoxy in 25-cm-
diameter circular grain mounts and polished until the
zircons were just revealed Images of the zircons were
obtained using the back-scatter electron (BSE) detector
on a Cameca SX50 electron microprobe The BSE
detector is a light-sensitive diode so the image
obtained of the internal structure of the zircon is a
combination of the variation in mean atomic number
(composition) as well as the cathodoluminescence
(CL) BSECL images were taken of all analysed
zircons to study the internal structure of the grains prior
to LA-ICP-MS analysis Grain mounts containing the
samples and standards were cleaned in 1 N nitric acid
immediately prior to analysis to remove surface Pb
contamination This removed the necessity for pre-
ablating the samples to remove surface contamination
22 Instrumentation
The laser ablation microprobe uses a focussed laser
beam to ablate a small amount of a sample contained
in a closed cell The ablated material is transported
from the cell in a carrier gas (Ar or He) to an ICP-MS
for isotopic quantification For the spot diameters
(mostly 50ndash80 Am) and ablation times (ca 60 s) used
in this study ablated masses of zircon were approx-
imately 500ndash1500 ng
Two laser ablation (LA) systems were used in this
study Most analyses were performed using a custom-
built UV LA sampler that has been described by
Norman et al (1996) The system incorporates a
frequency-quadrupled NdYAG laser (k=266 nm) and
beam delivery optics that attenuate the beam to the
required fluence and steer the beam down the photo-
tube of a petrographic microscope The microscope
incorporates specialised optics that focus the laser and
provide a high-quality image of the sample which
greatly facilitates locating sample sites in petrographic
mounts The sample mount and standardisation materi-
SE Jackson et al Chemical Geology 211 (2004) 47ndash6950
als were ablated in a sample cell approximately 8 cm in
diameter with a Teflon insert that holds up to four 25-
mm sample mounts A 05-mm restriction on the gas
inlet nozzle results in a jet-like flow across the samples
which results in amuchmore stable ablation signal than
a comparable cell without a restricted inlet nozzle The
ablated sample was transferred to the ICP-MS through
3 mm id PVC tubing that was cleaned by soaking in
02 N nitric acid prior to use and replaced on a monthly
basis
Ablation was performed in a He carrier gas (except
where noted otherwise) as first described by Eggins et
al (1998) The He carrier exiting the sample cell was
combined with Ar in a 30 cm3 mixing chamber prior to
entering the ICP The gas plumbing configuration
includes a two-way valve on the Ar line so that after
each ablation the user may switch the Ar to combine
with the He before entering the sample cell The ArndashHe
mixture flushes ablated particles from the cell much
faster than He alone resulting in a more rapid return of
signals to background levels and increased sample
throughput Operating conditions of the LA systems
are reported in Table 1
Constant LA operating conditions were maintained
throughout each analytical brunQ (18ndash22 analyses)
because elemental fractionation is extremely sensitive
to laser pulse energy and focus Moderate- to high-
power frequency-quadrupled NdYAG lasers require a
significant period (minutes) to attain stable output after
the initiation of lasing due largely to the thermal-
equilibration time of the temperature-sensitive 4th
harmonic crystal Constant ablation conditions were
achieved by leaving the laser firing continuously
throughout a run and initiating and terminating ablation
by unblocking and blocking the beam path
All analyses were performed with the laser focused
above the sample (typically ca 150ndash250 Am) This was
found to be a more robust method than bactivefocusingQ (Hirata and Nesbitt 1995) for reducing the
relative change in focus of the laser beam as it
penetrates into the sample since it does not require
optimisation of the vertical translation rate of
the stage for different laser operating conditions
(Jackson 2001) While greater defocusing reduces
ablation time-dependent fractionation of Pb and U it
increases the ablation spot size The degree of
defocusing was therefore set to give the maximum
crater diameter possible for a set of zircons The
266 nm laser system was used mostly for large zircons
where large spot sizes (60ndash80 Am in diameter) were
appropriate
Also evaluated in this study was a commercial
LUV213 laser ablation system (k=213 nm) (New
Wave ResearchMerchantek) The LUV213 was used
primarily for analysis of small zircons (b60 Am)
which can be difficult to ablate controllably at 266 nm
due to the high transmittance of the laser beam
through the grain into the underlying epoxy mounting
medium Due to the greater absorption of the 213 nm
laser beam the incidence of catastrophic ablation was
significantly reduced Most of the 213 nm laser data
presented here are for smaller spots (40ndash50 Am) than
produced with the 266 nm laser
The LUV213 was used with an in-house built
sample cell similar to that used on the 266 nm laser
except for a smaller cell diameter (ca 6 cm)
necessitated by space limitations Much lower beam
energies enter the harmonic generators in this system
compared to the 266 nm laser sampler due to the
lower output energy of the laser and the optical
configuration of the system Thus the 213 nm laser
sampler does not require a significant stabilisation
period after initiating ablation and no pre-ablation
warm up was used
The ICP-MS used was an Agilent 4500 a high-
sensitivity quadrupole ICP-MS that provides a sensi-
tivity of in excess of 200 million counts per second
(cps)ppm for mono-isotopic heavy elements (atomic
mass N85) in standard solutionmode Current detection
limits for these elements using laser ablation sampling
are typically b10 ppb for a 60-s analysis at 40ndash50 Amsampling resolution ICP-MS operating conditions
were generally optimised using continuous ablation
of our in-house GJ-1 zircon standard to provide
maximum sensitivity for the high masses (PbndashU) while
maintaining low oxide formation (ThO+Th+b15)
Few analyses give signals in excess of 2000000 cps
and thus all readings were made in pulse counting
mode employing a dead-time correction applied
automatically by the ICP-MS operating system
Instrumental background was established by the
standard procedure of measurement of a bgas blankQie analysis of the carrier gas with no laser ablation
(eg Hirata andNesbitt 1995 Fernandez-Suarez et al
1998 Horn et al 2000 Kosler et al 2002 Tiepolo et
al 2003 Tiepolo 2003) Adoption of this procedure
Table 1
LA-ICP-MS operating conditions and data acquisition parameters
ICP-MS
Model Agilent 4500
Forward power 1350 W
Gas flows
Plasma (Ar) 16 lmin
Auxiliary (Ar) 1 lmin
Carrier (He) 09ndash12 lmin
Make-up (Ar) 09ndash12 lmin
Shield torch Used for most
analyses
Expansion
chamber
pressure
350ndash360 Paa
LA Custom system LUV 213
Wavelength 266 nm 213 nm
Repetition rate 5 and 10 Hz 5 and 10 Hz
Pre-ablation laser
warm up
Laser fired
continuously
None
Pulse duration
(FWHM)
9 ns 5 ns
Apertured beam
diameteriris
setting
4 mm 15
Beam
expander setting
na 0
Focusing objective 10 fl = 20 mm 5 fl = 40 mm
Degree of
defocusing
150ndash250 Am(above sample)
Not known
Spot size 60ndash80 Am 40ndash50 AmIncident
pulse energy
ca 035 ca 01 mJ
Energy density
on sample
ca 12 J cm2 ca 8 J cm2
Data acquisition parameters
Data acquisition
protocol
Time-resolved analysis
Scanning mode Peak hopping 1 point
per peak
Detector mode Pulse counting
dead-time
correction applied
Isotopes
determined
206Pb 207Pb 208Pb232Th 238U
Dwell time
per isotope
15 30 10 10 15 ms
respectively
Quadrupole
settling time
ca 2 ms
Timescan ca 89 ms
Data acquisition (s) 180 s (60 s gas blank
up to 120 s ablation)
Table 1 (continued)
Samples and standrds
Mounts 25 mm diameter polished
grain mounts
Standard Gem zircon bGJ-1Q 609 Maa Pirani vacuum gauge may not be calibrated accurately for
ArHe mixtures
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 51
followed experiments to determine whether an
bablation blankQ (a blank measured while ablating)
might be a more appropriate measure of the true
background An ablation blank would take into account
any contribution to background derived from particles
released from the sample cell or transfer tubing wall by
the shock wave induced by laser ablation However
multiple ablations of high-purity synthetic fused silica
produced Pb Th and U count rates that were higher
than the gas background by an amount (median values
of b5 cps on 206Pb 207Pb and 238U b10 cps on 208Pb
and 232Th) that could reasonably have been derived
from Pb Th and U in the silica and in any case would
not significantly affect the vast majority of UndashPb
analyses (see the discussion of potential effect on208Pb232Th determination in Section 24)
For UndashPb work low gas background signals for Pb
are essential Low Pb gas backgrounds were achieved
by (1) careful attention to cleanliness of the LA system
(acid cleaning sample cell and inserts samples
delivery tubing) (2) dedicating the ICP-MS to laser
ablation analysis since analysis of solutions invariably
has a detrimental and long-term effect on Pb back-
grounds and (3) use of a liquid rather than a
compressed Ar supply Under these conditions typical
gas blank 208Pb signals of ca 30ndash40 cps were achieved
routinely Backgrounds were b10 cps for the other
elements of interest except Hg (ca 300 cps on 202Hg)
23 Data acquisition
Data acquisition parameters are listed in Table 1
Data were acquired on five isotopes using the
instrumentrsquos time-resolved analysis data acquisition
software The time-resolved analysis software reports
signal intensity data (cps) for each mass sweep
performed by the mass spectrometer This data
acquisition protocol allows acquisition of signals as a
function of time (ablation depth) and subsequent
recognition of isotopic heterogeneity within the abla-
tion volume (eg zones of Pb loss or common Pb
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 49
procedure is still required to correct instrumental mass
bias
Several studies have made use of a bjet cellQ whichintroduces the carrier gas as a high-velocity jet
directly onto the ablation site (Jackson et al 1996
Horn et al 2000 Jackson 2001) to reduce fractio-
nation together with calibration against a zircon
standard (eg Fernandez-Suarez et al 1998
Ketchum et al 2001) While the jet cell can produce
a significant reduction in fractionation (ca 50)
maintaining precise alignment of the carrier gas jet
onto the ablation site is difficult and represents a
serious limitation to this cell design
Horn et al (2000) used an experimentally derived
mathematical procedure that relates fractionation to
spot geometry (at constant energy density) to correct
for ablation-related elemental fractionation together
with use of a Tl235U spike to correct for instrumental
mass bias This method requires elemental fractiona-
tion to be extremely reproducible from day to day It is
better suited to the flat energy profiles of excimer laser
systems (eg Horn et al 2000) than NdYAG
systems (Tiepolo et al 2003) for which the energy
distribution within the laser beam can vary signifi-
cantly depending upon laser tuning and operating
conditions
In this study we used a high-sensitivity quadrupole
ICP-MS coupled to a custom-built UV laser ablation
microprobe based on a frequency quadrupled NdYAG
laser (k=266 nm) Also evaluated was a commercial
frequency-quintupled (k=213 nm) laser ablation sys-
tem We describe and evaluate a simple technique that
employs spot ablations with no specific strategies to
minimise ablation-related elemental fractionation
Fractionation and instrumental mass bias are corrected
by direct calibration against a new zircon standard
analysed under carefully matched conditions using He
as the ablation gas to increase the reproducibility of the
PbU fractionation Time-resolved data acquisition is
employed to evaluate zircon homogeneity and to allow
selective integration of signals to minimise common
Pb contributions and Pb loss and thus to maximise
concordance TerandashWasserburg diagrams (Tera and
Wasserburg 1972) are also employed to assess and
correct for residual common Pb contributions These
procedures are evaluated using data for five zircons
ranging in age from 1065 to 7 Ma Two of these
zircons have been analysed more than 400 times over
more than a year by two instrument operators
allowing an exhaustive evaluation of the long-term
precision and accuracy of the technique
2 Analytical techniques
21 Sample preparation
All zircons were mounted in epoxy in 25-cm-
diameter circular grain mounts and polished until the
zircons were just revealed Images of the zircons were
obtained using the back-scatter electron (BSE) detector
on a Cameca SX50 electron microprobe The BSE
detector is a light-sensitive diode so the image
obtained of the internal structure of the zircon is a
combination of the variation in mean atomic number
(composition) as well as the cathodoluminescence
(CL) BSECL images were taken of all analysed
zircons to study the internal structure of the grains prior
to LA-ICP-MS analysis Grain mounts containing the
samples and standards were cleaned in 1 N nitric acid
immediately prior to analysis to remove surface Pb
contamination This removed the necessity for pre-
ablating the samples to remove surface contamination
22 Instrumentation
The laser ablation microprobe uses a focussed laser
beam to ablate a small amount of a sample contained
in a closed cell The ablated material is transported
from the cell in a carrier gas (Ar or He) to an ICP-MS
for isotopic quantification For the spot diameters
(mostly 50ndash80 Am) and ablation times (ca 60 s) used
in this study ablated masses of zircon were approx-
imately 500ndash1500 ng
Two laser ablation (LA) systems were used in this
study Most analyses were performed using a custom-
built UV LA sampler that has been described by
Norman et al (1996) The system incorporates a
frequency-quadrupled NdYAG laser (k=266 nm) and
beam delivery optics that attenuate the beam to the
required fluence and steer the beam down the photo-
tube of a petrographic microscope The microscope
incorporates specialised optics that focus the laser and
provide a high-quality image of the sample which
greatly facilitates locating sample sites in petrographic
mounts The sample mount and standardisation materi-
SE Jackson et al Chemical Geology 211 (2004) 47ndash6950
als were ablated in a sample cell approximately 8 cm in
diameter with a Teflon insert that holds up to four 25-
mm sample mounts A 05-mm restriction on the gas
inlet nozzle results in a jet-like flow across the samples
which results in amuchmore stable ablation signal than
a comparable cell without a restricted inlet nozzle The
ablated sample was transferred to the ICP-MS through
3 mm id PVC tubing that was cleaned by soaking in
02 N nitric acid prior to use and replaced on a monthly
basis
Ablation was performed in a He carrier gas (except
where noted otherwise) as first described by Eggins et
al (1998) The He carrier exiting the sample cell was
combined with Ar in a 30 cm3 mixing chamber prior to
entering the ICP The gas plumbing configuration
includes a two-way valve on the Ar line so that after
each ablation the user may switch the Ar to combine
with the He before entering the sample cell The ArndashHe
mixture flushes ablated particles from the cell much
faster than He alone resulting in a more rapid return of
signals to background levels and increased sample
throughput Operating conditions of the LA systems
are reported in Table 1
Constant LA operating conditions were maintained
throughout each analytical brunQ (18ndash22 analyses)
because elemental fractionation is extremely sensitive
to laser pulse energy and focus Moderate- to high-
power frequency-quadrupled NdYAG lasers require a
significant period (minutes) to attain stable output after
the initiation of lasing due largely to the thermal-
equilibration time of the temperature-sensitive 4th
harmonic crystal Constant ablation conditions were
achieved by leaving the laser firing continuously
throughout a run and initiating and terminating ablation
by unblocking and blocking the beam path
All analyses were performed with the laser focused
above the sample (typically ca 150ndash250 Am) This was
found to be a more robust method than bactivefocusingQ (Hirata and Nesbitt 1995) for reducing the
relative change in focus of the laser beam as it
penetrates into the sample since it does not require
optimisation of the vertical translation rate of
the stage for different laser operating conditions
(Jackson 2001) While greater defocusing reduces
ablation time-dependent fractionation of Pb and U it
increases the ablation spot size The degree of
defocusing was therefore set to give the maximum
crater diameter possible for a set of zircons The
266 nm laser system was used mostly for large zircons
where large spot sizes (60ndash80 Am in diameter) were
appropriate
Also evaluated in this study was a commercial
LUV213 laser ablation system (k=213 nm) (New
Wave ResearchMerchantek) The LUV213 was used
primarily for analysis of small zircons (b60 Am)
which can be difficult to ablate controllably at 266 nm
due to the high transmittance of the laser beam
through the grain into the underlying epoxy mounting
medium Due to the greater absorption of the 213 nm
laser beam the incidence of catastrophic ablation was
significantly reduced Most of the 213 nm laser data
presented here are for smaller spots (40ndash50 Am) than
produced with the 266 nm laser
The LUV213 was used with an in-house built
sample cell similar to that used on the 266 nm laser
except for a smaller cell diameter (ca 6 cm)
necessitated by space limitations Much lower beam
energies enter the harmonic generators in this system
compared to the 266 nm laser sampler due to the
lower output energy of the laser and the optical
configuration of the system Thus the 213 nm laser
sampler does not require a significant stabilisation
period after initiating ablation and no pre-ablation
warm up was used
The ICP-MS used was an Agilent 4500 a high-
sensitivity quadrupole ICP-MS that provides a sensi-
tivity of in excess of 200 million counts per second
(cps)ppm for mono-isotopic heavy elements (atomic
mass N85) in standard solutionmode Current detection
limits for these elements using laser ablation sampling
are typically b10 ppb for a 60-s analysis at 40ndash50 Amsampling resolution ICP-MS operating conditions
were generally optimised using continuous ablation
of our in-house GJ-1 zircon standard to provide
maximum sensitivity for the high masses (PbndashU) while
maintaining low oxide formation (ThO+Th+b15)
Few analyses give signals in excess of 2000000 cps
and thus all readings were made in pulse counting
mode employing a dead-time correction applied
automatically by the ICP-MS operating system
Instrumental background was established by the
standard procedure of measurement of a bgas blankQie analysis of the carrier gas with no laser ablation
(eg Hirata andNesbitt 1995 Fernandez-Suarez et al
1998 Horn et al 2000 Kosler et al 2002 Tiepolo et
al 2003 Tiepolo 2003) Adoption of this procedure
Table 1
LA-ICP-MS operating conditions and data acquisition parameters
ICP-MS
Model Agilent 4500
Forward power 1350 W
Gas flows
Plasma (Ar) 16 lmin
Auxiliary (Ar) 1 lmin
Carrier (He) 09ndash12 lmin
Make-up (Ar) 09ndash12 lmin
Shield torch Used for most
analyses
Expansion
chamber
pressure
350ndash360 Paa
LA Custom system LUV 213
Wavelength 266 nm 213 nm
Repetition rate 5 and 10 Hz 5 and 10 Hz
Pre-ablation laser
warm up
Laser fired
continuously
None
Pulse duration
(FWHM)
9 ns 5 ns
Apertured beam
diameteriris
setting
4 mm 15
Beam
expander setting
na 0
Focusing objective 10 fl = 20 mm 5 fl = 40 mm
Degree of
defocusing
150ndash250 Am(above sample)
Not known
Spot size 60ndash80 Am 40ndash50 AmIncident
pulse energy
ca 035 ca 01 mJ
Energy density
on sample
ca 12 J cm2 ca 8 J cm2
Data acquisition parameters
Data acquisition
protocol
Time-resolved analysis
Scanning mode Peak hopping 1 point
per peak
Detector mode Pulse counting
dead-time
correction applied
Isotopes
determined
206Pb 207Pb 208Pb232Th 238U
Dwell time
per isotope
15 30 10 10 15 ms
respectively
Quadrupole
settling time
ca 2 ms
Timescan ca 89 ms
Data acquisition (s) 180 s (60 s gas blank
up to 120 s ablation)
Table 1 (continued)
Samples and standrds
Mounts 25 mm diameter polished
grain mounts
Standard Gem zircon bGJ-1Q 609 Maa Pirani vacuum gauge may not be calibrated accurately for
ArHe mixtures
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 51
followed experiments to determine whether an
bablation blankQ (a blank measured while ablating)
might be a more appropriate measure of the true
background An ablation blank would take into account
any contribution to background derived from particles
released from the sample cell or transfer tubing wall by
the shock wave induced by laser ablation However
multiple ablations of high-purity synthetic fused silica
produced Pb Th and U count rates that were higher
than the gas background by an amount (median values
of b5 cps on 206Pb 207Pb and 238U b10 cps on 208Pb
and 232Th) that could reasonably have been derived
from Pb Th and U in the silica and in any case would
not significantly affect the vast majority of UndashPb
analyses (see the discussion of potential effect on208Pb232Th determination in Section 24)
For UndashPb work low gas background signals for Pb
are essential Low Pb gas backgrounds were achieved
by (1) careful attention to cleanliness of the LA system
(acid cleaning sample cell and inserts samples
delivery tubing) (2) dedicating the ICP-MS to laser
ablation analysis since analysis of solutions invariably
has a detrimental and long-term effect on Pb back-
grounds and (3) use of a liquid rather than a
compressed Ar supply Under these conditions typical
gas blank 208Pb signals of ca 30ndash40 cps were achieved
routinely Backgrounds were b10 cps for the other
elements of interest except Hg (ca 300 cps on 202Hg)
23 Data acquisition
Data acquisition parameters are listed in Table 1
Data were acquired on five isotopes using the
instrumentrsquos time-resolved analysis data acquisition
software The time-resolved analysis software reports
signal intensity data (cps) for each mass sweep
performed by the mass spectrometer This data
acquisition protocol allows acquisition of signals as a
function of time (ablation depth) and subsequent
recognition of isotopic heterogeneity within the abla-
tion volume (eg zones of Pb loss or common Pb
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6950
als were ablated in a sample cell approximately 8 cm in
diameter with a Teflon insert that holds up to four 25-
mm sample mounts A 05-mm restriction on the gas
inlet nozzle results in a jet-like flow across the samples
which results in amuchmore stable ablation signal than
a comparable cell without a restricted inlet nozzle The
ablated sample was transferred to the ICP-MS through
3 mm id PVC tubing that was cleaned by soaking in
02 N nitric acid prior to use and replaced on a monthly
basis
Ablation was performed in a He carrier gas (except
where noted otherwise) as first described by Eggins et
al (1998) The He carrier exiting the sample cell was
combined with Ar in a 30 cm3 mixing chamber prior to
entering the ICP The gas plumbing configuration
includes a two-way valve on the Ar line so that after
each ablation the user may switch the Ar to combine
with the He before entering the sample cell The ArndashHe
mixture flushes ablated particles from the cell much
faster than He alone resulting in a more rapid return of
signals to background levels and increased sample
throughput Operating conditions of the LA systems
are reported in Table 1
Constant LA operating conditions were maintained
throughout each analytical brunQ (18ndash22 analyses)
because elemental fractionation is extremely sensitive
to laser pulse energy and focus Moderate- to high-
power frequency-quadrupled NdYAG lasers require a
significant period (minutes) to attain stable output after
the initiation of lasing due largely to the thermal-
equilibration time of the temperature-sensitive 4th
harmonic crystal Constant ablation conditions were
achieved by leaving the laser firing continuously
throughout a run and initiating and terminating ablation
by unblocking and blocking the beam path
All analyses were performed with the laser focused
above the sample (typically ca 150ndash250 Am) This was
found to be a more robust method than bactivefocusingQ (Hirata and Nesbitt 1995) for reducing the
relative change in focus of the laser beam as it
penetrates into the sample since it does not require
optimisation of the vertical translation rate of
the stage for different laser operating conditions
(Jackson 2001) While greater defocusing reduces
ablation time-dependent fractionation of Pb and U it
increases the ablation spot size The degree of
defocusing was therefore set to give the maximum
crater diameter possible for a set of zircons The
266 nm laser system was used mostly for large zircons
where large spot sizes (60ndash80 Am in diameter) were
appropriate
Also evaluated in this study was a commercial
LUV213 laser ablation system (k=213 nm) (New
Wave ResearchMerchantek) The LUV213 was used
primarily for analysis of small zircons (b60 Am)
which can be difficult to ablate controllably at 266 nm
due to the high transmittance of the laser beam
through the grain into the underlying epoxy mounting
medium Due to the greater absorption of the 213 nm
laser beam the incidence of catastrophic ablation was
significantly reduced Most of the 213 nm laser data
presented here are for smaller spots (40ndash50 Am) than
produced with the 266 nm laser
The LUV213 was used with an in-house built
sample cell similar to that used on the 266 nm laser
except for a smaller cell diameter (ca 6 cm)
necessitated by space limitations Much lower beam
energies enter the harmonic generators in this system
compared to the 266 nm laser sampler due to the
lower output energy of the laser and the optical
configuration of the system Thus the 213 nm laser
sampler does not require a significant stabilisation
period after initiating ablation and no pre-ablation
warm up was used
The ICP-MS used was an Agilent 4500 a high-
sensitivity quadrupole ICP-MS that provides a sensi-
tivity of in excess of 200 million counts per second
(cps)ppm for mono-isotopic heavy elements (atomic
mass N85) in standard solutionmode Current detection
limits for these elements using laser ablation sampling
are typically b10 ppb for a 60-s analysis at 40ndash50 Amsampling resolution ICP-MS operating conditions
were generally optimised using continuous ablation
of our in-house GJ-1 zircon standard to provide
maximum sensitivity for the high masses (PbndashU) while
maintaining low oxide formation (ThO+Th+b15)
Few analyses give signals in excess of 2000000 cps
and thus all readings were made in pulse counting
mode employing a dead-time correction applied
automatically by the ICP-MS operating system
Instrumental background was established by the
standard procedure of measurement of a bgas blankQie analysis of the carrier gas with no laser ablation
(eg Hirata andNesbitt 1995 Fernandez-Suarez et al
1998 Horn et al 2000 Kosler et al 2002 Tiepolo et
al 2003 Tiepolo 2003) Adoption of this procedure
Table 1
LA-ICP-MS operating conditions and data acquisition parameters
ICP-MS
Model Agilent 4500
Forward power 1350 W
Gas flows
Plasma (Ar) 16 lmin
Auxiliary (Ar) 1 lmin
Carrier (He) 09ndash12 lmin
Make-up (Ar) 09ndash12 lmin
Shield torch Used for most
analyses
Expansion
chamber
pressure
350ndash360 Paa
LA Custom system LUV 213
Wavelength 266 nm 213 nm
Repetition rate 5 and 10 Hz 5 and 10 Hz
Pre-ablation laser
warm up
Laser fired
continuously
None
Pulse duration
(FWHM)
9 ns 5 ns
Apertured beam
diameteriris
setting
4 mm 15
Beam
expander setting
na 0
Focusing objective 10 fl = 20 mm 5 fl = 40 mm
Degree of
defocusing
150ndash250 Am(above sample)
Not known
Spot size 60ndash80 Am 40ndash50 AmIncident
pulse energy
ca 035 ca 01 mJ
Energy density
on sample
ca 12 J cm2 ca 8 J cm2
Data acquisition parameters
Data acquisition
protocol
Time-resolved analysis
Scanning mode Peak hopping 1 point
per peak
Detector mode Pulse counting
dead-time
correction applied
Isotopes
determined
206Pb 207Pb 208Pb232Th 238U
Dwell time
per isotope
15 30 10 10 15 ms
respectively
Quadrupole
settling time
ca 2 ms
Timescan ca 89 ms
Data acquisition (s) 180 s (60 s gas blank
up to 120 s ablation)
Table 1 (continued)
Samples and standrds
Mounts 25 mm diameter polished
grain mounts
Standard Gem zircon bGJ-1Q 609 Maa Pirani vacuum gauge may not be calibrated accurately for
ArHe mixtures
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 51
followed experiments to determine whether an
bablation blankQ (a blank measured while ablating)
might be a more appropriate measure of the true
background An ablation blank would take into account
any contribution to background derived from particles
released from the sample cell or transfer tubing wall by
the shock wave induced by laser ablation However
multiple ablations of high-purity synthetic fused silica
produced Pb Th and U count rates that were higher
than the gas background by an amount (median values
of b5 cps on 206Pb 207Pb and 238U b10 cps on 208Pb
and 232Th) that could reasonably have been derived
from Pb Th and U in the silica and in any case would
not significantly affect the vast majority of UndashPb
analyses (see the discussion of potential effect on208Pb232Th determination in Section 24)
For UndashPb work low gas background signals for Pb
are essential Low Pb gas backgrounds were achieved
by (1) careful attention to cleanliness of the LA system
(acid cleaning sample cell and inserts samples
delivery tubing) (2) dedicating the ICP-MS to laser
ablation analysis since analysis of solutions invariably
has a detrimental and long-term effect on Pb back-
grounds and (3) use of a liquid rather than a
compressed Ar supply Under these conditions typical
gas blank 208Pb signals of ca 30ndash40 cps were achieved
routinely Backgrounds were b10 cps for the other
elements of interest except Hg (ca 300 cps on 202Hg)
23 Data acquisition
Data acquisition parameters are listed in Table 1
Data were acquired on five isotopes using the
instrumentrsquos time-resolved analysis data acquisition
software The time-resolved analysis software reports
signal intensity data (cps) for each mass sweep
performed by the mass spectrometer This data
acquisition protocol allows acquisition of signals as a
function of time (ablation depth) and subsequent
recognition of isotopic heterogeneity within the abla-
tion volume (eg zones of Pb loss or common Pb
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Table 1
LA-ICP-MS operating conditions and data acquisition parameters
ICP-MS
Model Agilent 4500
Forward power 1350 W
Gas flows
Plasma (Ar) 16 lmin
Auxiliary (Ar) 1 lmin
Carrier (He) 09ndash12 lmin
Make-up (Ar) 09ndash12 lmin
Shield torch Used for most
analyses
Expansion
chamber
pressure
350ndash360 Paa
LA Custom system LUV 213
Wavelength 266 nm 213 nm
Repetition rate 5 and 10 Hz 5 and 10 Hz
Pre-ablation laser
warm up
Laser fired
continuously
None
Pulse duration
(FWHM)
9 ns 5 ns
Apertured beam
diameteriris
setting
4 mm 15
Beam
expander setting
na 0
Focusing objective 10 fl = 20 mm 5 fl = 40 mm
Degree of
defocusing
150ndash250 Am(above sample)
Not known
Spot size 60ndash80 Am 40ndash50 AmIncident
pulse energy
ca 035 ca 01 mJ
Energy density
on sample
ca 12 J cm2 ca 8 J cm2
Data acquisition parameters
Data acquisition
protocol
Time-resolved analysis
Scanning mode Peak hopping 1 point
per peak
Detector mode Pulse counting
dead-time
correction applied
Isotopes
determined
206Pb 207Pb 208Pb232Th 238U
Dwell time
per isotope
15 30 10 10 15 ms
respectively
Quadrupole
settling time
ca 2 ms
Timescan ca 89 ms
Data acquisition (s) 180 s (60 s gas blank
up to 120 s ablation)
Table 1 (continued)
Samples and standrds
Mounts 25 mm diameter polished
grain mounts
Standard Gem zircon bGJ-1Q 609 Maa Pirani vacuum gauge may not be calibrated accurately for
ArHe mixtures
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 51
followed experiments to determine whether an
bablation blankQ (a blank measured while ablating)
might be a more appropriate measure of the true
background An ablation blank would take into account
any contribution to background derived from particles
released from the sample cell or transfer tubing wall by
the shock wave induced by laser ablation However
multiple ablations of high-purity synthetic fused silica
produced Pb Th and U count rates that were higher
than the gas background by an amount (median values
of b5 cps on 206Pb 207Pb and 238U b10 cps on 208Pb
and 232Th) that could reasonably have been derived
from Pb Th and U in the silica and in any case would
not significantly affect the vast majority of UndashPb
analyses (see the discussion of potential effect on208Pb232Th determination in Section 24)
For UndashPb work low gas background signals for Pb
are essential Low Pb gas backgrounds were achieved
by (1) careful attention to cleanliness of the LA system
(acid cleaning sample cell and inserts samples
delivery tubing) (2) dedicating the ICP-MS to laser
ablation analysis since analysis of solutions invariably
has a detrimental and long-term effect on Pb back-
grounds and (3) use of a liquid rather than a
compressed Ar supply Under these conditions typical
gas blank 208Pb signals of ca 30ndash40 cps were achieved
routinely Backgrounds were b10 cps for the other
elements of interest except Hg (ca 300 cps on 202Hg)
23 Data acquisition
Data acquisition parameters are listed in Table 1
Data were acquired on five isotopes using the
instrumentrsquos time-resolved analysis data acquisition
software The time-resolved analysis software reports
signal intensity data (cps) for each mass sweep
performed by the mass spectrometer This data
acquisition protocol allows acquisition of signals as a
function of time (ablation depth) and subsequent
recognition of isotopic heterogeneity within the abla-
tion volume (eg zones of Pb loss or common Pb
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6952
related to fractures or areas of radiation damage also
inclusions inherited cores etc) The signals can then
be selectively integrated Useful data could not be
acquired for 204Pb due to the large isobaric interference
from Hg a significant contaminant apparently derived
from the Ar supply or Ar supply piping and fittings Hg
signals could not be reduced sufficiently using filters to
allow useful analyses (see below)
A fast peak hopping protocol (dwell time per
isotope from 10 to 30 ms) was used to ensure
representative measurement of rapidly transient sig-
nals typical of laser ablation sampling This protocol
resulted in a full mass sweep time of ca 89 ms Given
the instrument-set mean quadrupole settling time of
ca 2 ms this is a reasonable compromise between the
conflicting ideals of maximum possible scanning
speed (to approximate simultaneous detection) and
overall counting efficiency (duty cycle) Each 3-min
analysis consisted of ca 60 s of measurement of
instrumental background (ie analysis of carrier gas
no ablation) followed by the ablation event (up to
120 s) giving a total analysis time of 3 min
Mass discrimination of the mass spectrometer and
residual elemental fractionation were corrected by
calibration against a standard zircon GJ-1 Samples
were analysed in brunsQ of ca 18ndash22 analyses
which included 10 unknowns A typical run com-
menced with two analyses of the zircon standard (or
more in the event of disagreement between the first
two analyses) This was followed by analyses of the
two near-concordant zircons 91500 (Wiedenbeck et
al 1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every run in our laboratory as
an independent control on reproducibility and
accuracy These were followed by two more
analyses of the GJ-1 standard then up to 10
unknowns followed by two (or more) analyses of
the GJ-1 standard This protocol results in a
minimum of six analyses of the zircon standard in
each run A minimum of six analyses is required to
identify and reject anomalous analyses of the stand-
ard and to correct drift in isotope ratios during the
run (typically 2 h)
24 GJ-1 standard
Fractionation of Pb and U during laser ablation and
inherent mass bias of all mass spectrometers must be
corrected to produce accurate ages In this study both
effects were corrected by external standardisation
Since the degree of ablation-related fractionation is
significantly matrix-dependent a zircon standard was
used The standard employed in this work was a large
(1 cm) gem quality pink zircon GJ-1 one of a bag of
similar pink (and yellow) zircons acquired from a
Sydney gem dealer The grain shows no zoning under
CL imaging LA-ICP-MS trace element analyses
show that the zircon is relatively low in Th with
mean U and Th contents of 230 and 15 ppm
respectively The chondrite-normalised REE pattern
is characterised by very low La (b01 chondrite) a
strong positive Ce anomaly no Eu anomaly and Lu at
ca 280 times chondrite
TIMS analyses were performed on eight aliquots
(two fragments from each of four grains) at the
University of Oslo by F Corfu The results are
presented in Table 2 and in Fig 1 TIMS analyses
provide a highly precise 207Pb206Pb age of
6085F04 Ma 206Pb204Pb ratios in excess of
146000 and U contents ranging 212ndash422 ppm
making it a potentially highly suitable standard The
disadvantage of this zircon standard is that it is not
concordant and while TIMS 206Pb238U and207Pb235U ratios for fragments of individual grains
vary by b06 there are small variations in these
ratios between grains (ca 1)
For standardising UndashPb analyses several large
grains (up to 1 cm in diameter) were investigated for
isotopic homogeneity by multiple LA-ICP-MS anal-
yses The grain that provided the most reproducible
ratios was subsequently adopted as the calibration
standard For the 207Pb206Pb 207Pb235U and206Pb238U ratios the weighted means of the TIMS
values have been adopted as the working ratios (see
Table 2) 208Pb232Th ratios were not measured
directly by TIMS but model ratios have been
calculated from the 208Pb206Pb ratios Using the
mean of the TIMS model ratios (003011) as the
working value for GJ-1 has resulted consistently in
young LA-ICP-MS208 Pb232 Th ages for all zircons
that we have measured relative to their TIMS UndashPb
ages On the basis of LA-ICP-MS calibration against
other zircons a value of 003074 has been adopted in
our laboratory as the working value for the208Pb232Th ratio in GJ-1 This value has been
employed in this study The difference between this
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Table 2
TIMS analyses of the GJ-1 zircon standard
Apparent age
Fraction Weight
(Ag)Pb
(ppm)
U
(ppm)
ThU Pbcom
(pg)
206204 207235
ratio
207235
2r (abs)
206238
ratio
206238
2r (abs)
rho 207206
ratio
207206
2r (abs)
208232
(model)
206238
(Ma)
207235
(Ma)
207206
(Ma)
(1) (2) (2) (2) (3) (4) (5) (6) (7) (6) (7) (6) (7) (8)
GJ-1-4 51 2949 195 215 006 9 420650 08125 00022 009801 000025 098 006012 000003 0030262 6027 6038 6080
GJ-1-4 52 1519 193 212 006 14 146133 08126 00018 009796 000020 098 006016 000003 0030249 6025 6039 6094
GJ-1-3 53A 6119 279 313 002 26 452072 08067 00034 009729 000040 099 006013 000003 0030048 5985 6006 6083
GJ-1-3 53B 6119 279 313 002 22 533252 08064 00030 009725 000035 099 006013 000003 0030036 5983 6004 6084
GJ-1-2 56 3144 374 422 002 13 612660 08034 00030 009689 000035 099 006014 000003 0029928 5962 5988 6086
GJ-1-2 59 2876 333 373 002 11 610787 08068 00027 009729 000031 099 006014 000003 0030047 5985 6007 6088
GJ-1-1 61A 4800 202 224 003 39 170396 08119 00033 009792 000039 099 006013 000003 0030237 6022 6035 6083
GJ-1-1 61B 4800 201 224 003 12 543384 08074 00027 009738 000032 099 006013 000003 0030074 5991 6010 6084
Wt Mean 08093 00009 009761 000011 006014 000001 0030110
91500 58A 738 141 77 035 55 11494 18476 00100 017890 000096 099 007491 000005 0053879 10609 10626 10660
91500 58B 738 140 77 034 10 62869 18543 00037 017948 000032 097 007493 000004 0054054 10641 10650 10667
Eight aliquots (two fragments from each of four grains) Zircon 91500 was also analysed for quality control purposes Analyses performed at the University of Oslo by Fernando
Corfu
(1) One zircon fragment in each fraction A and B denote fractions split after spiking dissolution and HCl re-equilibration but before chemical separation
(2) Weights better than 05 U and Pb concentrations probably F10 (spike concentration uncertainty)
(3) ThU model ratio inferred from 208206 ratio and age of sample
(4) Pbc=initial common Pb
(5) Total common Pb in sample (initial+blank)
(6) Raw data corrected for fractionation and blank
(7) Corrected for fractionation spike blank and initial common Pb (estimated from Stacey and Kramers (1975) model)
(8) Error calculated by propagating the main sources of uncertainty error does not include uncertainty of UndashPb ratio in spike about 01 based on spike calibration results
(9) Model 208Pb232Th ratio calculated from 208206 ratio assuming same degree of discordance as UndashPb ratios
SEJackso
net
alChem
icalGeology211
(2004)47ndash69
53
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 1 UndashPb concordia plot of TIMS analyses of the GJ-1 zircon standard
SE Jackson et al Chemical Geology 211 (2004) 47ndash6954
value and the TIMS model 208Pb232Th ratio could be
explained by an interference as small as ca 10 cps on
the LA-ICP-MS 208Pb signals for GJ-1 Thus a
possible explanation is a small contribution to the208Pb signal from ablation-induced enhancement of
the blank (median value of 7 cps in our experimentsmdash
see discussion in Section 22) possibly with additional
minor contributions to the 208Pb signal from poly-
atomic ion interference(s) (eg 96Zr216O+ 176Yb16O2
+176LuO2
+ 176HfO2+) Due to the very low Th (ca 15
ppm) and thus 208Pb contents of the GJ-1 zircon the
relative effect of these interferences would be much
larger on this zircon than on most others that we have
analysed This would explain the slightly young
measured 208Pb232Th ages for zircons calibrated
against GJ-1 using the TIMS model 208Pb232Th ratio
Further work is required to establish unequivocally the
true 208Pb232Th ratio of the GJ-1 zircon as some
common Pb corrections that are not based on 204Pb
determination (eg Andersen 2002) rely on accurate
determination of the 208Pb232Th ratio
25 Samples
The samples for which data are presented in this
study are two zircons 91500 (Wiedenbeck et al
1995) and Mud Tank (Black and Gulson 1978)
which are analysed in every analytical run in our
laboratory as quality control standards and three
young zircon samples (417ndash7 Ma) analysed numer-
ous times in a single analytical session The 91500
and Mud Tank zircons have each been analysed more
than 400 times over more than a year by two
instrument operators using both 266 and 213 nm
ablation systems The three zircons analysed repeat-
edly in a single analytical session were the Temora
zircon distributed by Geoscience Australia as a
microbeam UndashPb standard the Walcha Road zircon
(Flood and Shaw 2000) and the Gunung Celeng
(Indonesia) zircon
3 Data processing
31 GLITTER software
The raw ICP-MS data were exported in ASCII
format and processed using GLITTER (Van Achter-
bergh et al 2001) an in-house data reduction
program GLITTER calculates the relevant isotopic
ratios (207Pb206Pb 208Pb206Pb 208Pb232Th206Pb238U and 207Pb235U where 235U=238U13788)
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 55
for each mass sweep and displays them as a coloured
pixel map and as time-resolved intensity traces
Ratios were examined carefully for anomalous
portions of signal related to zones of Pb loss and
or common Pb gain inherited cores and occasional
surface Pb contamination not removed by acid
cleaning For both laser systems ratios generally
stabilised within 5ndash10 s of initiating ablation after
which data could be integrated The most concordant
segments of each ablation signal were generally
selected for integration Because of the ablation time
dependence of elemental fractionation GLITTER
automatically uses for each selected ablation time
segment of an unknown the identical integrated
ablation time segments of the standard zircon
analyses (relative to the commencement of ablation)
Net background-corrected count rates for each
isotope were used for calculation GLITTER corrects
the integrated ratios for ablation-related fractionation
and instrumental mass bias by calibration against the
zircon standard using an interpolative correction
(usually linear) for drift in ratios throughout the
run based on the six or more analyses of the
standard It then calculates ratios ages and errors
GLITTER does not apply a common Pb correction
Calculated ratios were exported and concordia ages
and diagrams were generated using Isoplot v 249
(Ludwig 2001)
32 Error propagation
In GLITTER isotope ratios are derived from
background-subtracted signals for the relevant iso-
topes Uncertainties in these ratios combine the
uncertainties of signal and background arising from
counting statistics and are added in quadrature The
same propagation is used for unknowns and standard
analyses The standard ratios are interpolated
between standard measurements to estimate the
standard ratios at the time of the measurement of
the unknowns Uncertainties in the standard ratio
measurements are propagated through this procedure
to estimate the standard ratio uncertainties relevant to
each unknown ratio measurement Relative uncer-
tainties estimated for the standard ratios are com-
bined with the unknown ratio uncertainties in
quadrature A further 1 uncertainty (1r) is
assigned to the measured TIMS values of the isotope
ratios for the standard and propagated through the
error analysis
33 Common Pb correction
In conventional TIMS analysis 204Pb is measured
to correct for common Pb present in the sample or
added during preparation of the sample for analysis
Initial attempts to measure 204Pb during this study
proved fruitless owing to the overwhelming contribu-
tion to the signal from 204Hg (isotopic abun-
dance=687) Typical gas blank signals at mass
204 were ca 300 cps Previous attempts to lower Pb
backgrounds on a VG PQII+bSQ ICP-MS at Memorial
University of Newfoundland using a Hg trap con-
sisting of glass tubes of gold-coated sand on the
carrier gas line resulted in a ca 50 reduction in Hg
signal that was still insufficient to allow a useful 204Pb
correction (Jackson unpublished data) Addition of
extra traps on the carrier gas and other ICP gas lines
resulted in little additional reduction in Hg intensity
suggesting that some of the Hg background is long-
term instrument memory In light of the similar Hg
background signals on the Agilent 4500 ICP-MS no
attempt was made to filter Hg on the ICP-MS used in
this study
In this study two main approaches to common Pb
reduction correction have been employed (1) selec-
tive integration of time-resolved signals and (2) Terandash
Wasserburg diagrams The common Pb correction
procedure described by Andersen (2002) was also
tested This procedure determines the amount of
common Pb by solving the mass-balance equations
for lead isotopes in a zircon and correcting the data
back to a three-dimensional Pb loss discordia line
However this correction is very sensitive to the
measured 208Pb232Th ratio Because of the low 208Pb
and 232Th concentrations and the uncertainty in the
true 208Pb232Th ratio of the GJ-1 standard this
method could not be used effectively in this study
331 Selective integration of time-resolved signals
The ability to selectively integrate LA-ICP-MS
time-resolved signals is frequently overlooked The
ablation surface penetrates into the sample at a rate
that is on the order of 01 Ampulse (05 Ams at 5 Hz
repetition rate) that is in any analysis the sampling
occurs on a scale where it may encounter significant
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6956
chemical or isotopic variations related to alteration
inclusions fractures and inherited cores and on a time
scale where transient signals related to these features
are commonly resolvable using a fast data acquisition
protocol Each analysis therefore records a profile of
the elemental and isotopic composition of the sample
with depth In many zircons common Pb and Pb loss
occur in restricted domains (along fractures zircon
rims) which can be recognised easily in time-resolved
signals of ablations that penetrate into such a domain
Using appropriate software signals and their ratios
can be displayed and selectively integrated so that
only the most isotopically concordant portions of
signals are integrated thereby hugely reducing the
incidence of analyses affected by common Pb and Pb
loss Fig 2 shows a striking example of an ablation
which contains useful data from 65 to 95 s at which
point the laser beam penetrated a zone which has
undergone significant radiogenic Pb loss and common
Pb gain with relative magnitudes that result in lower206Pb238U and 208Pb232Th ratios but higher207Pb206Pb and 207Pb235U ratios Selectively inte-
grating the data from ca 65 to 95 s produces an
Fig 2 Time-resolved isotope ratio traces for an ablation of a zircon from
95 s at which point the laser beam penetrated a domain that had under
analysis that is within error of the concordia at the
correct age for the sample
332 TerandashWasserburg diagrams
For young zircons containing a significant amount
of common Pb plotting of data on TerandashWasserburg
diagrams (Tera and Wasserburg 1972) was found to
be the most effective method of evaluating and
correcting for contributions from common Pb This
is discussed more fully below with reference to the
Walcha Road and Gunung Celeng zircons
4 Results
41 Short-term precision (266 and 213 nm)
The short-term (2 h) precision of the method has
been evaluated by multiple analyses of an isotopically
homogeneous grain of our zircon standard GJ-1 The
266 nm laser ablation has been compared with 213 nm
ablation using both Ar and He as ablation gases The
GJ-1 zircon was analysed 10 times using nominally
the Walcha Road pluton Useful data were recorded between 65 and
gone substantial loss of radiogenic Pb and gain of common Pb
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 3 Precision expressed as relative standard deviation (1r) of the measured ratios for ablation in Ar and He using 266 and 213 nm laser
ablation of GJ-1 zircon under nominally the same focusing and irradiance conditions (10 analyses of each combination of laser and ablation
gas) 60 s ablations ca 50 Am spot size
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 57
the same conditions (spot size=50 Am pulse energy
025 mJ measured at the sample 10 Hz repetition rate
60 s of data integrated) for each laser system External
precisions (1r) for the four combinations of laser and
ablation gas are presented in Fig 3
The most striking feature of the data is the dramatic
improvement in precision for ablations in He com-
pared to ablations in Ar For ablations in He
Fig 4 Signals for ablation of GJ-1 zircon in Ar and He (266 nm laser) A
signals
precisions on both PbU ratios were close to 1
with very slightly improved RSDs for 213 nm
ablations compared to 266 nm Comparison of
ablation signals (266 nm) (Fig 4) show that ablation
in He resulted in generally larger more stable signals
with very significantly less short-term (1 s) noise
reflecting the higher proportion of small particles
(b05 Am) in the ablation volume that is characteristic
blation in He produces generally larger more stable and less noisy
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6958
of ablation in He (Horn and Gunther 2003) However
the ca 2-fold greater signal intensities for ablations in
He cannot explain the 3- to 5-fold improvement in
precisions for the UndashPb ratios compared to ablation in
Ar Comparison of PbU fractionation trends (Fig 5)
reveals that while ablation in He did not result in
reduced PbU fractionation relative to ablation in Ar
it did produce significantly more reproducible fractio-
nation trends particularly during the first 60 s of
ablation The reason for the initial drop in PbU ratio
for ablations in Ar may relate to a burst of large
particles in the early stages of ablation Incomplete
vaporisation of these particles in the ICP results in
preferential volatilisation of the more volatile ele-
ments (eg Pb) over more refractory elements (eg
U) (Guillong and Gunther 2002) and thus high PbU
ratios in the early stages of an ablation The larger
proportion of small particles that are transported
during ablation in He might mask this effect
Ablation in He resulted in substantially improved
precisions for 207Pb206Pb measurements compared to
ablation in Ar reflecting higher signals and reduced
short-term noise in signals The 207Pb206Pb ratios
were for all lasergas combinations much more
precise than the PbU ratios suggesting that the
limiting factor on precision of PbU ratios was not
counting statistics but reproducibility of PbU frac-
tionation during ablation together with spatial varia-
Fig 5 Measured 206Pb238U ratios for ablation of GJ-1 zircon in Ar and H
laser) Note the two Ar analyses highlighted which show significantly dif
tions in the PbU ratios within the sample
Interestingly the 266 nm laser produced an approx-
imately twofold improvement in precision of the207Pb206Pb ratio for ablations in Ar and He
compared to the 213 nm laser a statistic that cannot
be explained fully by the 30 higher count rates
Based on the data above all further analyses were
performed using He as the ablation gas To
determine the precision of the method over the
course of a typical analytical run 20 consecutive
analyses of the GJ-1 zircon standard were performed
(266 nm laser) using typical ablation conditions (60 s
ablation 50 Am spot diameter) The mean ratios for
the first and last four analyses of the GJ-1 standard
were used to calibrate the run and correct any drift
in ratios throughout the run The external precisions
(2r) on the 206Pb238U 207Pb235U and 207Pb206Pb
ratios were 19 30 and 24 respectively (Fig
6) These compare with mean internal precisions
(2r) for the 20 analyses of 07 19 and 19
which are close to the predicted precisions based on
counting statistics alone (06 17 and 18
respectively) Again small differences in elemental
fractionation between analyses together with real
variations in the PbU ratios within the sample can
explain the significantly higher external precisions
than internal precisions for the 206Pb238U and207Pb235U ratios
e (five analyses of each) using identical ablation conditions (266 nm
ferent fractionation trends during the first 50 s of ablation
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 6 Concordia plot of 20 consecutive analyses of gem zircon standard GJ-1 demonstrating 2r reproducibility of 206Pb238U and 207Pb235U
ratios of better than 2 and 4 respectively
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 59
42 Long-term precision and accuracy
The long-term precision and accuracy of the
technique has been established via repeated analyses
of two zircons 91500 (Wiedenbeck et al 1995) and
Mud Tank (Black and Gulson 1978) which are
analysed as unknowns for quality control purposes in
every analytical run conducted in our laboratories
421 91500
The 91500 zircon one of the most widely used
zircon reference materials in existence is derived
from a single large crystal in a syenite from Renfrew
County Ontario It has a 207Pb206Pb age based on 11
TIMS determinations of 10654F03 Ma (Wieden-
beck et al 1995) Reported U concentrations of the
aliquots analysed ranged from 71 to 86 ppm
The data presented here were acquired by two
analysts between May 2001 and October 2002 The
266 nm and 213 nm laser systems were used for 372
and 88 analyses respectively Because of the smaller
spot sizes used for the 213 nm laser analyses the
magnitudes of the signals for these analyses were on
average ca 50ndash60 of the signals for the 266 nm
laser analyses There are no systematic differences in
the data from the two operators and their data have
been pooled Two highly anomalous analyses one
from each laser system (207Pb206Pb ratio N6 and N20
sd from the mean 213 and 266 nm data respec-
tively) were rejected during data acquisition and are
not discussed further
A frequency distribution diagram of the 266 nm
laser 206Pb238U data (Fig 7) reveals a slightly skewed
bell curve with a low age tail and a few outliers on
each side of the curve The low age outliers are
presumed to be related largely to Pb loss The older
outliers do not show high 207Pb206Pb ages which
would accompany a common Pb problem or inherited
component They are reversely discordant due most
probably to redistribution of Pb within the zircon
crystal or to anomalous laser-induced PbU fractiona-
tion A summary of the data for the 91500 zircon is
presented in Table 3 (complete data set may be
accessed from the online data repository (see Appen-
dix A)) with anomalous analyses that lie outside the
bell curvemdashages greater than 1110 Ma (four analyses)
and less than 990 Ma (12 analyses)mdashrejected from
statistical analysis
A frequency distribution diagram of the 213 nm
laser 206Pb238U data shows a generally similar age
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 7 Frequency distribution diagram for 371 206Pb238U age determinations of the 91500 zircon using the 266 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 355 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6960
distribution to the 266 nm laser data including several
positive outliers (Fig 8) However in contrast to the
266 nm laser data there is no tailing on the low age
side of the bell curve For statistical analysis only the
four positive outliers with ages greater than 1110 Ma
were rejected (Table 3)
The precisions of the 207Pb206Pb 206Pb238U and207Pb235U ages derived using the two laser systems are
remarkably similar and are almost all within a factor of
2 of the measured short-term precisions of the
technique reported above 207Pb206Pb ages for both
systems are in close agreement with the TIMS age
However statistically significant differences exist in
the PbU ages produced by the two laser systems
(differences of 11 and 9 Ma for the weighted mean206Pb238U and 207Pb235U ages respectively) The
Table 3
Summary of LA-ICP-MS and TIMS UndashPb isotopic ages for the 91500 zi
Isotopic ratios Mean age (Ma)
266 nm (n=355) 213 nm (n=83) 266 nm (n=355) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Me
207Pb206Pb 00749 14 00750 13 1065 28 106207Pb235U 18279 40 18491 44 1055 27 106206Pb238U 01771 38 01789 37 1051 37 106208Pb232Th 00532 72 00538 155 1048 74 105
213 nm laser 206Pb238U weighted mean age is in
perfect agreement with the TIMS 206Pb238U age but
the 266 nm laser age for this system is 12 Ma younger
Several explanations exist for the low age skew
exhibited by the 266 nm laser data not displayed in
the 213 nm laser data and the consequent discernibly
younger age produced Some of the early 266 nm laser
analyses of the 91500 zircon were performed on a
different grain mount than that used for the 213 nm
analyses However there are no discernible differences
in the ages obtained for the two mounts The skew may
therefore be a function of the larger spot size and
greater penetration depth of the 266 nm laser spots
which might have resulted in increased incidence of
intercepting domains (fractures) along which Pb loss
has occurred There is also a possibility that the
rcon TIMS data from Wiedenbeck et al 1995
Weighted mean age (Ma)Ferrors
(at 95 confidence)
TIMS age (Ma)
nm (n=83) 266 nm (n=355) 213 nm (n=83) Mean 2r
an 2 sd Mean error Mean error
8 26 1065 25 1068 57 10654 03
3 29 1055 14 1064 33
1 36 1050 19 1061 40 10624 04
8 159 1045 35 1049 16
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 8 Frequency distribution diagram for 87 206Pb238U age determinations of the 91500 zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on 83 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 61
different mean ages derived from the two laser systems
result from a systematic difference in PbU elemental
fractionation between the 91500 and GJ-1 standard
zircon as a result of a small difference at 266 nm in
laser beam absorption which was significantly reduced
at the more absorbing shorter wavelength (213 nm)
Fig 9 Frequency distribution diagram for 364 206Pb238U age determinatio
MeanF2 sd and weighted meanFuncertainty at 95 confidence based o
422 Mud Tank zircon
The Mud Tank zircon derives from one of only a
few carbonatites known in Australia The Mud Tank
carbonatite is located in the Strangways Range
Northern Territory The zircon dated is a large (ca
1 cm) megacryst A UndashPb concordia intercept age of
ns of the Mud Tank zircon using the 266 nm laser ablation system
n 359 analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6962
732F5 Ma was reported by Black and Gulson (1978)
based on five TIMS analyses (an additional aberrant
analysis was rejected) four of which lie very close to
concordia Errors on individual data points were not
quoted Reported U concentrations of the aliquots
analysed ranged from 6 to 36 ppm However 16 LA-
ICP-MS trace element analyses of our sample ranged
from 11 to 131 ppm (Belousova 2000) and the mean
LA-ICP-MS U signal for the crystal analysed in this
study was 20 higher than the signal for the 91500
zircon (reported U concentrations=71ndash86 ppm Wie-
denbeck et al 1995)
The data presented here were acquired by the same
two analysts and over the same period as the 91500
analyses The 266 nm and 213 nm laser systems were
used for 365 and 73 analyses respectively As for the
91500 analyses signal intensities for the 213 nm laser
analyses were on average ca 60ndash70 of the signals
for the 266 nm laser analyses Again there are no
systematic differences in the data from the two
operators and their data have been pooled One highly
anomalous analysis performed on the 266 nm laser
(207Pb206Pb ratio N7 sd from the mean) was rejected
during data acquisition and is not considered further
A frequency distribution diagram of 266 nm laser206Pb238U data (Fig 9) reveals a symmetrical bell
curve with a few outliers on the lower and upper side of
the curve reflecting significant Pb loss and reverse
discordance respectively For statistical analysis
(Table 4) extreme outliers with ages greater than 780
Ma (four analyses) and less than 680 Ma (one analysis)
were rejected (complete data set may be accessed from
the online data repository (see Appendix A))
A frequency distribution diagram of 213 nm laser206Pb238U data (Fig 10) is a perfectly symmetrical
bell curve with no outliers and all data have been
accepted for statistical analysis The lack of outliers
Table 4
Summary of LA-ICP-MS isotopic ages for the Mud Tank zircon (TIMS a
Isotopic ratios Mean age (Ma)
266 nm (n=359) 213 nm (n=73) 266 nm (n=359) 213
Mean 2 rsd Mean 2 rsd Mean 2 sd Mea
207Pb206Pb 00639 17 00638 19 740 36 735207Pb235Pb 10607 41 10569 53 734 22 732206Pb238U 01204 39 01202 49 733 27 731208Pb232Th 00370 70 00372 97 734 50 738
in the 213 nm laser data may reflect reduced
incidence of ablating through fractures in the zircon
due to the smaller spot size and reduced laser
penetration depth
The data for the two laser systems are compared in
Table 4 Because of the large uncertainty on the TIMS
age reported by Black and Gulson (1978) the Mud
Tank cannot be considered a precisely calibrated
zircon Nevertheless all LA-ICP-MS ages are within
error of the reported TIMS age As for the 91500
zircon data precisions for the two laser systems are
very similar Noticeable in this data set however is
the very close agreement of the 206Pb238U and207Pb235U ages for the two laser systems
43 Application of the technique to young zircons
The precision and accuracy of the technique for
dating younger samples (down to 8 Ma) are discussed
with reference to the Temora Walcha Road and
Gunung Celeng zircons
431 Temora zircon
The Temora zircon derives from a high-level
gabbro-diorite stock in the Lachlan Fold Belt near
Temora NSW Because of its availability and isotopic
integrity this zircon has been developed by Geo-
science Australia as a standard for SHRIMP dating of
Phanerozoic rocks U concentrations range from 60 to
600 ppm and TIMS analyses of 21 single grain
analyses were all concordant and gave an age of
4168F024 Ma (95 confidence limits based on
measurement errors alone) (Black et al 2003)
The grains analysed in this study ranged from ca
50 to 100 Am in diameter and showed little internal
structure under CLBSE Results for 15 analyses
performed using 266 nm laser ablation are presented
ge=732F5 Ma Black and Gulson 1978)
Weighted mean age (Ma)Ferrors (at 95 confidence)
nm (n=73) 266 nm (n=359) 213 nm (n=73)
n 2 sd Mean Error Mean Error
40 7396 28 7356 68
28 7339 11 7312 32
34 7324 14 7306 39
70 7323 26 7324 83
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 10 Frequency distribution diagram for 73 206Pb238U age determinations of the Mud Tank zircon using the 213 nm laser ablation system
MeanF2 sd and weighted meanFuncertainty at 95 confidence based on all analyses as discussed in the text
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 63
in Table 5 (complete data set may be accessed from
the online data repository (see Appendix A)) All data
lie on or very close to concordia The weighted mean206Pb238U and 207Pb235U ages (4150 and 4154 Ma)
are in good agreement with the TIMS age and the 2rerrors (32 and 34 Ma) on the weighted mean
represent a relative error of ca 08 The weighted
mean 206Pb238U age of the 11 most coincident points
Table 5
LA-ICP-MS ages (266 nm laser) for the Temora zircon (TIMS age 4168
Analysis no 207Pb206Pb F2 sd 206Pb238U F2
TEM-1 421 59 416 10
TEM-2 507 87 410 10
TEM-3 384 91 422 10
TEM-4 408 72 411 9
TEM-5 423 67 413 9
TEM-6 416 61 418 9
TEM-7 434 107 411 10
TEM-8 421 93 423 11
TEM-9 353 94 417 10
TEM-10 377 91 418 10
TEM-11 391 80 418 10
TEM-12 506 106 423 11
TEM-13 396 96 420 11
TEM-14 474 67 405 9
TEM-15 402 79 406 10
Weighted mean 4150 3
when plotted on a TerandashWasserburg diagram is
4167F29 Ma and probably represents the best
estimate of the age of this sample (Belousova and
Griffin 2001) Because of its isotopic homogeneity
the Temora zircon provides a good example of the
precision and accuracy attainable by LA-ICP-MS for
a sample in a single analytical run (15 analyses over
ca 2 h)
plusmn03 Ma Black et al 2003)
sd 207Pb235U F2 sd 208Pb232Th F2 sd
416 10 412 10
425 14 432 13
416 14 420 13
410 11 408 10
415 11 405 11
418 10 415 10
414 16 426 16
423 15 414 14
407 14 415 12
412 14 412 12
414 13 403 13
436 17 440 15
416 15 410 14
415 11 408 10
405 12 401 11
2 4154 32
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6964
432 Walcha Road zircon
The late Permian Walcha Road adamellite is a large
I-type zoned pluton in the New England batholith of
northern New South Wales It grades from a mafic
hornblende-biotite adamellite along themargin through
a K-feldspar-phyric adamellite into a fine grained
leuco-adamellite in the core of the pluton (Flood and
Shaw 2000) Zircon U concentrations range from
several hundred ppm in the periphery of the intrusion to
several thousand ppm in the core (S Shaw personal
communication) All zircons are small (most b50 Am)
and are variably metamict This sample therefore
represents a significant challenge for age dating
Fifty-one grains were dated including some from
each of the three phases of the pluton using the 266 nm
laser system with laser focusing conditions adjusted to
give ca 30ndash40 Am spots The 02123 zircon standard
(Ketchum et al 2001) was used for calibration as the
GJ-1 standard had not been developed at the time of
analysis Data from 11 grains were rejected during data
reduction from further consideration because of very
short ablations (b10 s) due to catastrophic failure of
the grain during ablation or extremely disturbed ratios
(N70 discordant) reflecting the high degree of
metamictisation of the grains
Fig 11 TerandashWasserburg plot for 40 zircon analyses from the Walcha roa
dark grey
ATerandashWasserburg plot of the remaining 40 grains
(Fig 11 complete data set may be accessed from the
online data repository (see Appendix A)) reveals a
cluster of points on concordia and an array of points
above concordia defining an apparent common Pb
discordia line Two points to the left of the line are
interpreted to reflect inheritance Points to the right of
the line are interpreted to have lost radiogenic Pb and
gained common Pb (see example shown in Fig 2) In
this case a graphical approach to interpreting the data
was favoured Rejection of all data with a very large
amount of common Pb (207Pb206PbN008) and points
not overlapping at 2r confidence the analyses defining
a common Pb array leaves 26 points that yield a
common Pb-anchored regression intercept age of 249F3
Ma (Fig 12) This is in perfect agreement with a RbSr
isochron age (based on 22 analyses of rock K-feldspar
plagioclase and biotite) of 248F2 Ma (MSWD=084)
(S Shaw unpublished data) Although ideally a high-
precision TIMS UndashPb date is required for this sample to
confirm the absolute accuracy of the LA-ICP-MS age
the close agreement of LA-ICP-MS and RbSr ages
suggests that with appropriate protocols LA-ICP-MS
can provide accurate ages even for zircons that have
gained significant amounts of common Pb
d pluton Analyses rejected from the regression in Fig 12 shown in
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
Fig 12 TerandashWasserburg plot with regression of 26 zircon analyses from the Walcha road pluton
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 65
433 Gunung Celeng zircon
The application of LA-ICP-MS to dating very
young zircons is demonstrated using a zircon from a
high-level intrusion emplaced into MiocenendashPliocene
volcanics in the Gunung Celeng area of Java
Fig 13 TerandashWasserburg plot of data
Indonesia The zircons are mostly elongated euhedral
grains with lengthwidth ratios varying from 2 to 4
and widths ranging from 50 to 80 Am Zircons from
these samples show obvious magmatic oscillatory
zoning on the BSECL images Twenty-five grains
from the Gunung Celeng zircon
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6966
from the Gunung Celeng area with U concentrations
ranging from ca 50 to 550 ppm (mean ca 335 ppm)
were analysed using the 266 nm laser ablation system
and a spot size of ca 60 Am Four grains ablated
catastrophically and no data were collected The
remaining 21 grains gave usable data (complete data
set may be accessed from the online data repository
(see Appendix A))
A TerandashWasserburg plot of these 21 data points
(Fig 13) shows evidence of common Pb contamina-
tion possibly due to ablation of epoxy mounting the
grains A common Pb-anchored regression of all the
data gave an intercept age of 69F02 Ma
(MSWD=29) Rejecting analyses with 207Pb206PbN
008 which were clearly compromised by a significant
amount of common Pb the remaining eight grains gave
a slightly older weighted mean 206Pb238U age of
71F01 (MSWD=022) which probably represents the
best estimate of the crystallisation age of this sample
Apatite from the same samples gave a UndashHe age of
50F026 Ma (B McInnis pers comm) The UndashHe
age which dates the time that the apatite cooled below
its He closure temperature (75 8C) represents a
minimum age for the Gunung Celeng zircons The
slightly older LA-ICP-MS UndashPb dates are therefore
consistent with this age although a TIMS UndashPb date is
required for this sample to confirm their absolute
accuracy
5 Discussion and conclusions
A new zircon standard GJ-1 has been developed
Multiple LA-ICP-MS analyses of single grains have
produced the best precision of any zircon that we have
studied including the Temora zircon standard This
together with its large grain size (ca 1 cm)
combination of relatively high U content (230 ppm)
and moderate age (ca 609 Ma) extremely high206Pb204Pb (in excess of 146000) make it a
potentially highly suitable standard for in situ zircon
analysis The major drawback of this standard is that it
is not concordant and ID-TIMS analyses reveal small
variations (ca 1) in 206Pb238U and 207Pb235U
ratios between grains While this variation is less than
the analytical precision of the LA-ICP-MS technique
it does ideally require that each individual grain of the
GJ-1 standard be calibrated individually
A number of protocols have been described in the
literature for calibrating UndashPb analyses by LA-ICP-
MS These procedures are required to correct for
elemental fractionation associated with laser ablation
and the sample transport and ionisation processes
together with the inherent mass bias of the ICP-MS
The procedures involve a combination of (1) external
standardisation which corrects both sources of
fractionation but requires a very good matrix-
matched standard a stable laser and ICP-MS and
very careful matching of ablation conditions for
sample and standard (Tiepolo et al 2003 Tiepolo
2003 this study) (2) rastered ablation (eg Li et al
2001 Horstwood et al 2001 Kosler et al 2002)
which significantly reduces the ablation time depend-
ence of elemental fractionation but results in degraded
spatial resolution (or requires use of a very small
beam which reduces the ablation rate and thus the
signalnoise ratio) Moreover while it has been
demonstrated that rastering effectively reduces time-
dependent change in element ratios during ablation it
may not necessarily provide the correct elemental
ratio because of elemental fractionation during
incomplete breakdown of large particles in the ICP
(Guillong and Gunther 2002) This method has been
used with (1) or (4) (below) to correct for instrumental
mass bias (3) an empirical correction for ablation-
related elemental fractionation (Horn et al 2000)
which requires a reproducibility of laser conditions
that is not easily attainable using NdYAG-based
systems (Tiepolo et al 2003) This method has been
used in conjunction with (4) to correct for instrumen-
tal mass bias (Horn et al 2000) (4) use of an on-line
spike (Tl233U or 235U) introduced into the carrier gas
stream to correct for instrumental mass bias (Horn et
al 2000 Kosler et al 2002) Use of a solution-based
spike can result in high Pb backgrounds (Kosler et al
2002) which compromises data for young andor low-
U zircons This method must be used with 1 2 or 3 to
correct for ablation-related bias
The results of this study demonstrate that using a
reliable zircon standard to correct the sources of
isotopic bias together with a stable and sensitive
quadrupole ICP-MS and appropriate time-resolved
data reduction software accurate U-Pb ages can be
produced with a precision (2 rsd) on single spot
analyses ranging from 2 to 4 By pooling 15 or
more analyses 2r precisions below 1 can readily be
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 67
achieved These figures of merit compare very
favourably with those produced using rastering or
experimentally derived corrections of PbU fractiona-
tion (eg Kosler et al 2002 Horn et al 2000)
together with on-line TlU spiking This performance
also compares well with that produced using a similar
calibration protocol to the one described on a double
focusing sector field mass spectrometer (single
collector) (Tiepolo et al 2003 Tiepolo 2003)
The main disadvantage of the calibration approach
described here is that identical ablation conditions
(spot size laser fluence integration time) must be
maintained for all analyses in a run This is most
problematic for zircon populations with widely differ-
ent grain sizes and for very small zircons where
short low energy ablations required for the sample
must also be used for the standard
Common Pb contributions can be addressed
adequately using a variety of strategies including
selective integration of signals and graphical evalua-
tion It should also be noted that at a typical analysis
rate of ca 40ndash50 unknowns per day rejection of a few
analyses because of high common Pb is rarely a
serious problem
The 213 nm laser ablation produces slightly better
precision than 266 nm ablation and offers much
better ablation characteristics particularly for small
zircons For zircon 91500 213 nm produced206Pb238U and 207Pb235U ages that were signifi-
cantly different (older by ca 10 Ma) than those
produced by 266 nm laser ablation and which
agreed perfectly with TIMS ages The 266 and 213
nm laser data for the Mud Tank zircon analysed in
the same runs are indistinguishable indicating that
the difference is not related to use of different grains
of the GJ-1 zircon standard for the 266 and 213 nm
laser analyses This strongly suggests that the
difference in the 266 and 213 nm ages is related
either to the different ablation volumes produced by
the two laser systems andor to small differences in
ablation behaviour of the 91500 and GJ-1 zircons at
266 nm and that reproducibility of fractionation
between sample and standard is better using the
more strongly absorbed shorter wavelength 213 nm
radiation However in either case there is no
evidence of a similar effect(s) with the Mud Tank
and Temora zircons indicating that the effect is not
universal
For most zircons analysed the external precisions
of the 206Pb238U and 207Pb235U ratios are despite
significantly different count rates very similar and
significantly poorer than the 207Pb206Pb ratios for
the same analyses (see for example Fig 3) This
may in part be due to heterogeneity of the zircons
through redistribution of Pb andor U within the
crystals However a significant contribution to this is
likely to be small differences in PbU fractionation
behaviour from analysis to analysis related to drift
in laser operating conditions slight differences in
laser focus etc If inability to reproduce PbU
fractionation is the major limiting factor on preci-
sion further gains in the technique must come from
improvements in the sampling system rather than in
the detection system In either case the fact that
attainable precisions on the PbU ratios are several
times poorer than predicted on the basis of counting
statistics suggests that use of multi-collector (MC)-
ICP-MS instruments may not yield significantly
better precision than single collector instruments
although simultaneous collection might allow meas-
urement of 204Pb with sufficient precision to provide
a useful common Pb correction
Acknowledgements
We are most grateful to Jerry Yakoumelos of G
and J Gems Sydney for the donation of the GJ-1
standard zircon and to Fernando Corfu for perform-
ing TIMS analyses of the GJ-1 zircon We thank
Ayesha Saeed for providing her LA-ICP-MS data
sets for the 91500 and Mud Tank zircons Brent
McInnes kindly provided the Gunung Celeng zircon
and supporting data and Lance Black provided the
Temora zircon Stirling Shaw kindly allowed us to
use his data set for the Walcha Road zircon and
provided supporting RbndashSr data Chris Ryan and
Esme van Achterberg developed the GLITTER data
reduction program that was used in this study Tom
Andersen kindly provided a copy of his common Pb
correction program CommPbCorr Ashwini Sharma
and Suzy Elhlou are thanked for their assistance with
the LA-ICP-MS analyses The authors would like to
thank Roland Mundil and Takafumi Hirata for their
careful reviews that substantially improved the
manuscript This is publication no 345 from the
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash6968
ARC National key Centre for Geochemical Evolu-
tion and Metallogeny of Continents (wwwesmq
eduauGEMOC) [PD]
Appendix A Supplementary data
Supplementary data associated with this article can
be found in the online version at doi101016
jchemgeo200406017
References
Andersen T 2002 Correction of common Pb in UndashPb analyses
that do not report 204Pb Chem Geol 192 59ndash79
Belousova EA 2000 Trace elements in zircon and apatite
application to petrogenesis and mineral exploration Unpub-
lished PhD thesis Macquarie University
Belousova EA Griffin WL 2001 LA-ICP-MS age of the
Temora zircon Unpublished data reported to Geoscience
Australia
Black LP Gulson BL 1978 The age of the Mud Tank
carbonatite Strangways Range Northern Territory BMR J
Aust Geol Geophys 3 227ndash232
Black LP Kamo SL Allen CM Aleinikoff JN Davis DW
Korsch RJ Foudoulis C 2003 TEMORA 1 a new zircon
standard for Phanerozoic UndashPb geochronology Chem Geol
200 155ndash170
Eggins SM Kinsley LPJ Shelley JMG 1998 Deposition and
element fractionation processes occurring during atmospheric
pressure sampling for analysis by ICP-MS Appl Surf Sci 129
278ndash286
Feng R Machado N Ludden J 1993 Lead geochronology
zircon by laser probe-inductively coupled plasma mass spec-
trometry (LP-ICPMS) Geochim Cosmachim Acta 57 3479ndash
3486
Fernandez-Suarez J Gutierrez-Alonso G Jenner GA Jackson
SE 1998 Geochronology and geochemistry of the Pola de
Allande granitoids (northern Spain) their bearing on the
CadomianAvalonian evolution of NW Iberia Can J Earth
Sci 35 1439ndash1453
Flood RH Shaw SE 2000 The Walcha Road adamellite a large
zoned pluton in the New England batholith Australia Geol
Soc Australian Abstr 59 152
Fryer BJ Jackson SE Longerich HP 1993 The application of
laser ablation microprobe-inductively coupled plasma-mass
spectrometry (LAM-ICP-MS) to in-situ (U)ndashPb geochronology
Chem Geol 109 1ndash8
Fryer BJ Jackson SE Longerich HP 1995 The design
operation and role of the laser-ablation microprobe coupled with
an inductively coupled plasma-mass spectrometer (LAM-ICP-
MS) in the earth sciences Can Min 33 303ndash312
Guillong M Gqnther D 2002 Effect of particle size distributionon ICP-induced elemental fractionation in laser ablation
inductively coupled plasma mass spectrometry J Anal At
Spectrom 17 831ndash837
Hirata T Nesbitt RW 1995 UndashPb isotope geochronology of
zircon evaluation of the laser probe-inductively coupled
plasma-mass spectrometry technique Geochim Cosmochim
Acta 59 2491ndash2500
Horn I Gqnther D 2003 The influence of ablation carrier gasses
Ar He and Ne on the particle size distribution and transport
efficiencies of laser ablation-induced aerosols implications for
LA-ICP-MS Appl Surf Sci 207 144ndash157
Horn I Rudnick RL McDonough WF 2000 Precise elemental
and isotope ratio determination by simultaneous solution
nebulization and laser ablation-ICP-MS application to UndashPb
geochronology Chem Geol 164 281ndash301
Horstwood MSA Foster GL Parrish RR Noble SR 2001
Common-Pb and inter-element corrected UndashPb geochronology
by LA-MC-ICP-MS VM Goldschmidt Conf Abstr 3698
Jackson SE 2001 The application of NdYAG lasers in LA-ICP-
MS In Sylvester PJ (Ed) Laser Ablation-ICP-Mass Spec-
trometry in the Earth Sciences Principles and Applications
Mineralog Assoc Canada (MAC) Short Course Series vol 29
Mineralogical Association of Canada pp 29ndash45
Jackson SE Horn I Longerich HP Dunning GR 1996 The
application of laser ablation microprobe (LAM)-ICP-MS to in
situ UndashPb zircon geochronology VM Goldschmidt Confer-
ence J Conf Abstr 1 283
Ketchum JWF Jackson SE Culshaw NG Barr SM 2001
Depositional and tectonic setting of the Paleoproterozoic Lower
Aillik Group Makkovik Province Canada evolution of a
passive marginmdashforedeep sequence based on petrochemistry
and UndashPb (TIMS and LAM-ICP-MS) geochronology Precam-
brian Res 105 331ndash356
Kosler J Fonneland H Sylvester P Tubrett M Pedersen R-
B 2002 UndashPb dating of detrital zircons for sediment
provenance studiesmdasha comparison of laser ablation ICP-MS
and SIMS techniques Chem Geol 182 605ndash618
Li X-H Liang X Sun M Guan H Malpas JG 2001 Precise206Pb238U age determination on zircons by laser ablation
microprobe-inductively coupled plasma-mass spectrometry
using continuous linear ablation Chem Geol 175 209ndash219
Ludwig KR 2001 Isoplot v 22mdasha geochronological toolkit for
Microsoft Excel Berkeley Geochronology Center Special
Publication No 1a 53 pp
Mank AJG Mason PRD 1999 A critical assessment of laser
ablation ICP-MS as an analytical tool for depth analysis in silica-
based glass samples J Anal At Spectrom 14 1143ndash1153
Norman MD Pearson NJ Sharma A Griffin WL 1996
Quantitative analysis of trace elements in geological materials
by laser ablation ICPMS instrumental operating conditions
and calibration values of NIST glass Geostand Newsl 20
247ndash261
Outridge PM Doherty W Gregoire DC 1997 Ablative and
transport fractionation of trace elements during laser sampling of
glass and copper Spectrochim Acta 52B 2093ndash2102
Stacey JS Kramers JD 1975 Approximation of terrestrial lead
isotope evolution by a two-stage model Earth Planet Sci Lett
26 207ndash221
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23
SE Jackson et al Chemical Geology 211 (2004) 47ndash69 69
Tera F Wasserburg GJ 1972 UndashThndashPb systematics in three
Apollo 14 basalts and the problem of initial Pb in lunar rocks
Earth Planet Sci Lett 14 281ndash304
Tiepolo M 2003 In situ Pb geochronology of zircon with laser
ablation-inductively coupled plasma-sector field mass spectrom-
etry Chem Geol 199 159ndash177
Tiepolo M Bottazzi P Palenzona M Vannucci R 2003 A
laser probe coupled with ICP-double focusing sector-field mass
spectrometer for in situ analysis of geological samples and UndashPb
dating of zircon Can Min 41 259ndash272
Van Achterbergh E Ryan CG Jackson SE Griffin WL 2001
Data reduction software for LA-ICP-MS appendix In Syl-
vester PJ (Ed) Laser Ablation-ICP-Mass Spectrometry in the
Earth Sciences Principles and Applications Mineralog Assoc
Canada (MAC) Short Course Series Ottawa Ontario Canada
vol 29 pp 239ndash243
Wiedenbeck M Alle P Corfu F Griffin WL Meier M
Oberli F von Quadt A Roddick JC Spiegel W 1995
Three natural zircon standards for UndashThndashPb LundashHf trace
element and REE analyses Geostand Newsl 19 1ndash23