He Pb double dating of detrital zircons from the Ganges and Indus Rivers: Implication for...

etters 237 (2005) 402–432

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Earth and Planetary Science L

He–Pb double dating of detrital zircons from the Ganges and Indus

Rivers: Implication for quantifying sediment recycling and

provenance studies

Ian H. Campbell a,*, Peter W. Reiners b, Charlotte M. Allen a,

Stefan Nicolescu b, Rajeev Upadhyay c

aResearch School of Earth Sciences, The Australian National University, Canberra, ACT, 0200 AustraliabDepartment of Geology and Geophysics, Yale University, Kline Geology Laboratory, 210 Whitney Ave., New Haven, CT 06511, USA

cDepartment of Geology, Kumaun University, Nainital-263002, India

Received 3 December 2004; received in revised form 6 June 2005; accepted 24 June 2005

Available online 9 August 2005

Editor: V. Courtillot

Abstract

He–Pb double dating of detrital zircons is more reliable than conventional U–Pb dating for tracing the source of detritus in

sediments and can be used to constrain the percentage of recycled material in sediments. Conventional U–Pb dating can be used

to constrain the provenance of sediments if the U–Pb zircon age pattern for potential source regions is known but can only be

used to trace the source of individual zircons if they are first-cycle grains. The advantages of He–Pb double dating are

demonstrated using examples from the Indus and Ganges rivers, and previously published data from the Navajo sandstone.

Conventional U–Pb dating can unambiguously identify only 2.5% of the Ganges zircons, and 18% of the Indus zircons as

coming from the Himalayan Mountains or Tibet Plateau and only 23% of the Navajo zircons as coming from the Appalachian

Mountains. The correct figure, as determined from double dating, is over 95% from the Himalayan Mountains or Tibet Plateau

in the case of the Indus and Ganges rivers and at least 70% from the Appalachian Mountains in the case of the Navajo

Sandstone. This result casts doubt on the reliability of the U–Pb method when used in the absence of other techniques, such as

He dating, to identify the true provenance of sediments, as opposed to the ultimate source of the zircons. Double dating also

shows that at least 60% of the Indus and 70% of the Ganges and Navajo sandstone zircons have been recycled from earlier

sediments. Exhumation rates, estimated from the He dates, reveal that ~75% of the Indus and Ganges zircons were derived from

areas where the exhumation rate exceeds 1.5 km/Myr. These rates are higher and more varied than those calculated from detrital

muscovites. These results imply that ~75% of the eroded material in the Himalayan Mountains is derived from areas of

anomalously high erosion where the short-term exhumation rate exceeds the long-term average.

D 2005 Elsevier B.V. All rights reserved.

Keywords: detrital zircons; Ganges; Indus; double dating; He–Pb dating; sedimentary recycling

* Corresponding author. Tel.: +61 2 6125 4366.

0012-821X/$ - s

doi:10.1016/j.ep

E-mail addre

ee front matter D 2005 Elsevier B.V. All rights reserved.

sl.2005.06.043

ss: [email protected] (I.H. Campbell).

I.H. Campbell et al. / Earth and Planetary Science Letters 237 (2005) 402–432 403

1. Introduction

(U–Th)/Pb dating of detrital zircons has become

an increasing popular means of tracing sediment

sources [1–5]. This is because rapid methods of

dating single crystals, using first ion probes and,

more recently, laser ablation inductively coupled

plasma mass spectrometry (laser ICP-MS), have

become more widespread. The problem with (U–

Th)/Pb dating of detrital zircons, as a means of

tracing the provenance of sediments, is that they

are strongly resistant to thermal resetting and melt-

ing, with closure temperatures in excess of 900 8C[6,7]. Furthermore, they are resistant to mechanical

abrasion and can pass through many cycles of sedi-

mentation. As a consequence, U–Pb dating of zir-

cons alone cannot distinguish between a first-cycle

zircon, derived directly from a primary igneous

rock, and a multi-cycle zircon derived from a sedi-

mentary rock. Grain texture (e.g., rounding), and the

compositional maturity of the host sediment are

Arabian Sea

INDIA

T

Gange

Indu

s Riv

er

Nanga Parbat

TH-1 GR-8

FI

Chenab

Sutlej

70o

10o N

80o

30o

20o

Fig. 1. Map of India and Tibet showing the location of Fig. 2, the location

major tributaries to these rivers. The Himalayan Mountains are shown in

often used to identify multi-cycled grains [8] but

Johnson et al. [9] have shown that these methods

are unreliable.

The distinction between primary first-cycle and

multi-cycle zircons has fundamental implications for

provenance studies. Primary first-cycle zircons are

igneous or meta-igneous minerals that crystallized

during the orogenic event that created the topogra-

phy from which the zircons were exhumed in the

most recent cycle of sedimentation. As a conse-

quence, they date the thermal-orogenic event that

is the true source of the detrital zircon. Multi-cycle

zircons are derived from sedimentary or meta-sedi-

mentary rocks that were caught up in an orogenic

event. They do not date the uplift–erosion event that

freed the zircon from its bedrock source for capture

in the sampled sediment, but earlier orogenic events

that may be hundreds of millions to billions of years

older that the event that led to exhumation. Age

patterns of zircons shed from potential source ter-

ranes, if known, can be used to constrain the pro-

Bay ofBengal

IBET

Everest

s RiverBrahmaputra

River

G. 2

100o E

90o

of samples TH-1 and GR-8, the Indus River, the Ganges River and

yellow.

I.H. Campbell et al. / Earth and Planetary Science Letters 237 (2005) 402–432404

venance of detrital zircons but the solution can be

ambiguous. Furthermore, if the sediment includes

zircons from two or more terranes, the mixed zircon

age patterns produced become difficult to decipher,

although it can be done under some circumstances

(e.g., [1]). Ion probe or laser ICP-MS can some-

times date metamorphic rims on zircons, which

form during the orogenic event that is the source

of the grain. However, metamorphic rims that are

wide enough to date by conventional ion probe or

laser ICP-MS methods are rare.

An alternative approach to identify source terranes

is to use low-temperature thermochronometers, such

as the fission track and (U–Th)/He dating of single

zircons or apatites, or Ar/Ar dating of detrital micas

and K-feldspars. These methods avoid the problem of

the thermal resistance of the U–Pb system in zircons

to resetting; they record exhumation ages (the time at

which the mineral passes through its closure tempera-

tures of ~100 to 300 8C, depending on the system)

rather than the age of the orogenic event from which

the mineral was eroded. Our preliminary studies,

using (U–Th)/He dating of detrital zircons, show

that the exhumation age can be as much as 250 Myr

younger than the age of the orogenic event that shed

the zircon.

This paper reports the results of a new dating pro-

cedure, which we call He–Pb double dating, that gives

both the high temperature (~900 8C) U–Pb crystalliza-tion and low temperature (~180 8C) (U–Th)/He exhu-mation ages for the same zircon [10,11]. It therefore

combines the advantages of both methods, which

aids distinguishing between first-cycle and multi-

cycle zircons. The utility of the method is illustrated

in a study of detrital zircons separated from two

modern sands from the Indus and Ganges rivers

(Fig. 1). The Ganges and Indus River sands were

selected for study because they derive the over-

whelming bulk of their sediment load from two

known sources, the Tibetan Plateau and the Himala-

yan Mountains. They provide the opportunity to test

the applicability of the He–Pb double-dating method

in a controlled environment; sediments shed from a

young, still topographically significant, orogenic

event. The power of the method is further illustrated

by using double-dated zircon data from the Navajo

sandstone of southwest Utah, previously reported by

Rahl et al. [10], to determine the percentage of

recycled material in a ~190 Ma sandstone. The

results show that multi-cycled zircons dominate the

detrital populations in all three of the studied sam-

ples, which has important implications for the appli-

cation of U–Pb detrital zircon dating in provenance

studies.

2. Geological setting

The Himalayan province consists mainly of a thick

pile of Proterozoic and Phanerozoic sediments from

the Purana (ancient) basins of northern India [12,13]

(Figs. 1 and 2). The Himalayas can be divided into

five terranes separated by boundary faults (Fig. 2).

The northern-most sediment-dominated terrane is the

Tethys Himalaya that consists principally of pre-colli-

sional Mesozoic to Tertiary continental arc-related

rocks and their Neoproterozoic to Ordovician base-

ment. It is locally deformed at the northern edge to

form a series of domes including the Nimaling-Tso

Morari (TM) and RakasTal-Gurla Mandhata domes

(GM). The northern margin of the Tethys Himalaya

is the Indus–Tsangpo Suture Zone (ITSZ), which

primarily puts the Tethys Himalaya in contact with

the Mesozoic to Tertiary calc alkaline arc rocks some-

times referred to as the bTranshimalayan BatholithQ(Kohistan Arc-Ladakh and Gangadese batholiths).

The bTranshimalayan BatholithQ is a continental mar-

ginal arc that was swept against the Asian continent

during north-dipping subduction of Neo-tethys ocea-

nic crust preceding true continent–continent collision.

The Tethys Himalaya is separated from the high-grade

metamorphosed sediments of the Central Crystallines

of the Greater Himalaya to the south by the South

Tibetan Fault System (STFS). The Greater Himalaya

ranges in age from Neoproterozoic to Ordovician and

includes pelitic and psammitic schists, calc-silicate

gneiss, marble, augen gneiss and migmatite [14],

which were intruded by mid-Tertiary leucogranites

(red in Fig. 2) and Cambro-Ordovician (450–600

Ma) granites. The Main Central Thrust (MCT) sepa-

rates them from the sediments of the Lesser Himalaya.

The Lesser Himalayan rocks are dominated by Middle

Proterozoic to Lower Cambrian sediments but are

overlain above a prominent unconformity by Permian

and younger strata. The Lesser Himalaya has been

metamorphosed to low and medium grades and is

˚78˚68˚58˚48˚38˚28˚18˚08˚97˚87˚77˚67˚57˚47E˚88

˚13

˚23

˚33

˚72

˚82

˚92

˚03

Key to Acronyms

ITSZ

ITSZ

ITSZ

NP

MCTS

MCTS

MCTS

MB

TS

MB

TS

MBTS

ITSZ

MCTSMCTS

EVMCTS

MBTS

STFSSTFS

STFS

STFS

STFS

GM

?

100 km

ZTMM

SSZ

SSZ

TMMFT

N˚63

43 ˚

35˚

˚27 ˚37˚17

EV - EverestGM - Gulra Mandhata DomeHU - HunzaITSZ - Indus Tsangpo Suture ZoneKW - Kishtwar WindowMBTS - Main Boundary Thrust SystemMCTS - Main Central Thrust SystemMFT - Main Frontal FaultNP - Nanga ParbatSTFS - South Tibetan Fault SystemTM - Tso Morani Dome

RThrust FaultHigh-Angle Reverse FaultHigh-Angle Normal FaultLow to Moderate Angle FaultTranscurrent FaultFault with Unknown Displacement

KW

Kohistan Arc

Ganges Drainage

Indus Drainage

Islamabad

Delhi

Drainate DivideIntermontane Basins (Neogene-Quaternary)Cenozoic Foreland (Silalik Terrane)Leococratic Plutons (Miocene)Transhimalayan batholith (Mesozoic-Tertiary)Tethyan HimalayaCentral Crystallines of the Greater HimalayaLesser Himalaya

HU

STFS

Fig. 2. Geological sketch map of the Himalaya and Tibetan Plateau showing the location of the Tethys Himalaya, the Kohistan–Ladakh Arc–Transhimalayan Batholith, the Central

Crystallines of the Greater Himalaya, the Lesser Himalaya, the Cenozoic foreland basin sediments of the Siwalik terrane, and the major faults and thrusts that separate these terranes.

The outline of the drainage basins, for the Indus and Ganges rivers, emphasizes the differences in the major rock types that these rivers pass through. The Indus system largely samples

the Tibetan side of the Himalayas whereas the Ganges drains the southern slopes, including the Greater Himalaya, where Miocene leucogranites occur. Triangles mark the two major

peaks, Everest (EV) and Nanga Parbat (PN), and a circle the Hunza (HU) region. Simplified and expanded from [16].

I.H.Campbell

etal./Earth

andPlaneta

ryScien

ceLetters

237(2005)402–432

405


intimately associated with tectonically emplaced

mylonitised 1900F100 Ma porphyritic granites. The

pre-Ordovician rocks, in both the Lesser and Greater

Himalaya, have been intruded by 500F25 Ma gran-

ites and granodiorites [12]. Below the Lesser Hima-

laya, and separated by the Main Boundary Thrust

System (MBTS), are the Cenozoic foreland basin

sediments, which are locally called the Siwalik Ter-

rane. The Himalayan Frontal Fault System separates

these rocks from the Holocene sediments of the Indo-

Ganges Plain.

The Greater and the Tethys Himalaya are intruded

by leucogranites that range in size from a few

centimeters to a hundred kilometers ([15,16] and

reference therein). Most were emplaced between 12

and 23 Ma ([16–18] and references therein) and they

are interpreted to be the product of crustal melting

[15].

3. Method

The Indus sample was collected near the mouth of

the river [19] and the two Ganges samples (GR-8

and GR-9) 700 km up river from the Bangladesh

boarder, near Kanpur (Fig. 1). The zircons were

separated using conventional magnetic and heavy

liquid separation techniques. Conventional Excimer

Laser Ablation Inductively Coupled Plasma Mass

Spectrometry (ELA-ICP-MS) and the He–Pb dou-

ble-dating method were used to date the grains.

ig. 3. A sketch of the mounts used in the conventional and rim piercing methods for dating detrital zircons. When zircons are dated in a

onventional mount (A) the zircon is sectioned in half and polished so that the rim is exposed only as a narrow zone at the margin of the grain,

hich is normally too narrow to date by conventional means. The rim piercing method (B) involves mounting the unsectioned grain on adhesive

pe and drilling directly into the rim at the top of the grain.

F

c

w

ta

Zircons selected for conventional dating were

mounted in epoxy resin and polished (Fig. 3A).

Optical photomicrographs were used to map and

select least-fractured and inclusion free material for

analysis. The zircons selected for He–Pb double

dating [10,11] were mounted as whole grains on

double-sided adhesive tape and dated by the U–Pb

method, using an ELA-ICP-MS. The zircons were

then removed from the tape and dated by the (U–

Th)/He method (He dating). Optical photomicro-

graphs were again used as maps to identify the

grains selected for analyses, but the quality of the

image is poor compared with the image obtained

from epoxy mounts. The laser holes for U–Pb dating

are drilled through the top of unprepared grains (Fig.

3B). This procedure, which is called the rim-piecing

method, provides a continuous profile of Pb206/U238

over 20 Am, and therefore the age variation, from the

rim of the grain towards its center. It is ideal for

dating grains that show age zoning. The U–Pb dating

method used in this study is described in Appendix

A and the He method by Reiners et al. [20]. Dating

two granites from the northern Sierra Nevada, by both

this method and by conventional laser ICP-MS ana-

lyses, tested the reliability of the rim-piecing method.

The weighted average ages and associated errors (two

standard errors) obtained for 15 grains from each

sample by the conventional ELA-ICP-MS method

were 123.2F1.6 (MSWD=0.61) and 123.7F2.3

(MSWD=1.47), which compares with 122.2F3.7

(MSWD=1.78) and 122.6F2.0 (MSWD=0.53) res-

Fig. 4. Histograms and cumulative density plots of U–Pb ages for all zircons from the Indus and Ganges rivers. Analyses that meet the

acceptance criteria for good analyses are shown in black on the histograms and rejected analyses in white. Only accepted analyses are shown on

the cumulative probability plot.



pectively by the rim-piecing method. The He–Pb

double-dating method was tested by dating nineteen

zircons separated from the Fish Canyon Tuff [11]. The

ig. 5. Histogram and cumulative probability plot of U–Pb ages for zircons younger than 600 Ma from the Indus and Ganges rivers. Analyses

at meet the acceptance criteria for good analyses are shown in black on the histograms and rejected analyses in white. Only accepted analyses

re shown on the cumulative probability plot.

F

th

a

dates obtained were 28.8F1.8 (2 standard deviations)

by the U–Pb method, and 28.6F2.7 by the He

method.


4. Results

4.1. Conventional ELA-ICP-MS dating

The results for the conventional ELA-ICP-MS U–

Pb dating for the Indus and Ganges river zircons are

summarized in Figs. 4 and 5 and the Ganges data are

listed in Table 1 and are presented as a Concordia

plot in Fig. 6. The Indus data are taken from Clift et

al. [19]. Nine peaks can be recognized in the Indus

data: at 25, 60–90, 120, 525, 750–800, 925, 1000,

1850 and 2500 Ma. Note that only nine or 7% of 133

analyzed grains have ages less than 55 Ma, the

approximate age of the India–Eurasia collision [16].

Five of these zircons have U–Pb ages between 15 and

25 Ma and 4 have ages close to 50 Ma. Five peaks

can be recognized in the Ganges data: 450–500, 760–

1000, 1100–1220, 1740–1900 and 2450–2550 Ma.

The dominant peak is the one at 700–1000 Ma and

only six of 213 grains, or 3%, have an age less than

55 Ma.

4.2. He–Pb double dating

The U–Pb and He ages for the Indus and Ganges

zircons, selected for He–Pb double dating, are listed in

Table 2 and He ages are plotted in Fig. 7. Only zircons

with an accumulated radiation dosage of less than

2�1018 a/g have been included in this study to

remove the possibility of He loss in metamict grains,

which leads to geologically meaningless young ages

([20], and references therein). All but one of the

analyzed zircons has U–Pb ages greater than 55 Ma,

whereas all but one of the He dates are less than 55

Ma. The zircon with an He age greater than 55 Ma has

an U–Pb age of 1487 Ma and an He age of 443 Ma.

Fig. 7 shows that 21 of the 27 (~75%) of the double-

dated zircons have He ages less than 5 Ma and three

of the six remaining grains have ages of ~15 Ma.

5. Discussion

It is logical to expect that the principal source of

river sediment will be the dominant mountain range in

the basin drained by that river. In the case of the Indus

and Ganges rivers, the principal sediment sources are

obviously the Himalayan Mountains and Tibetan Pla-

teau. Orogenic events, of the type that produced the

Himalayan Mountains and Tibetan Plateau, can be

expected to contain three types of zircon. (i) Primary

first-cycle zircons produced by the crustal melting

event associated with the uplift that shed the zircons.

Their U–Pb ages date the orogenic (uplift) event that

is the true provenance of the zircons. (ii) Secondary

first-cycle zircons that come from pre-orogenic

igneous events that are caught up in the orogenic

event that shed the detrital zircons. They can be

used in provenance studies if the age and location of

their igneous source are known, but their U–Pb age

dates an event that is older than the orogenic event

that is the source of the zircon. (iii) Multi-cycle zir-

cons derived from sediments. Their U–Pb ages date

multiple thermo-orogenic events that are the ultimate

source of the detrital zircons. These events are older

than the thermo-orogenic events in the true prove-

nance of the sediment and they are of limited value

in provenance studies. It is therefore essential to

develop a method that can distinguish between pri-

mary first-cycle, secondary first-cycle and multi-cycle

zircons before detrital zircons can be confidently

assigned to a provenance.

5.1. Primary first-cycle zircons

Primary first-cycle zircons are of two types: volca-

nic and plutonic. Identifying volcanic primary-first-

cycle zircons is trivial; their U–Pb and (U–Th)/He

ages agree within analytical error. There are no pri-

mary first-cycle volcanic zircons in the Indus or

Ganges rivers but we have identified them in sedi-

ments, which include volcanic debris, from North

America (e.g., the Missouri River). Identifying pluto-

nic first-cycle zircons is more challenging because

their low-temperature He age will be younger than

their high temperature U–Pb age. However, the dif-

ference between their U–Pb and He ages, which we

define as DT, is the time between granite formation

and exhumation through the 180 8C isotherm. DT will

vary from one thermo-orogenic event to the next,

depending on its rate of uplift and erosion. An arbi-

trary value of 300 Myr has been used, which is

consistent with the data presented in this paper and

with our unpublished data for the Missouri and Mis-

sissippi rivers. This value may need to be revised as

more data become available and it may be appropriate

Table 1

ELA-ICP-MS U–Th–Pb age determinations

Date\analysis ID Rim-piercing

Mount?

Pb*

(ppm)

U

(ppm)

Atomic

Th/U

Uncorr’d206Pb/238U

ratio

F1s.e. Uncorr’d207Pb/235U

ratio

F1s.e. Uncorr’d207Pb/206Pb

ratio

F1s.e. Uncorr’d208Pb/232Th

ratio

F1s.e. %Common206Pb

using 208Pb

%Common206Pb using207Pb


age

(Ma)

011025\GR9-001 168.7 753.1 0.084 0.25883 0.00095 3.53078 0.01982 0.09894 0.00042 0.07774 0.00063 �0.029 0.763 1483.9

011025\GR9-002 217.6 714.3 0.195 0.34714 0.00282 5.39073 0.06283 0.11263 0.00094 0.09489 0.00115 �0.288 �0.641 1920.9

011025\GR9-003 25.4 215.9 1.384 0.13511 0.00043 1.25961 0.01220 0.06762 0.00062 0.03999 0.00022 �2.142 0.156 816.9

011025\GR9-046 1.3 276.1 0.006 0.00571 0.00011 0.05176 0.00268 0.06578 0.00315 0.03063 0.00265 1.415 2.399 36.7

011025\GR9-004 84.9 680.2 0.674 0.14327 0.00037 1.34826 0.00760 0.06825 0.00034 0.04365 0.00018 �0.562 0.053 863.1

011025\GR9-005 74.0 322.2 0.325 0.26766 0.00100 3.97010 0.03940 0.10758 0.00099 0.07675 0.00195 �0.330 1.574 1528.9

011025\GR9-006 7.3 97.3 0.153 0.08669 0.00080 0.73413 0.02830 0.06142 0.00230 0.00909 0.00060 �1.519 0.398 535.9

011025\GR9-006 17.6 148.4 0.701 0.13675 0.00106 1.30619 0.02833 0.06927 0.00140 0.04570 0.00071 0.586 0.323 826.3

011025\GR9-007 139.1 572.2 0.888 0.27937 0.00077 3.84546 0.01776 0.09983 0.00037 0.08600 0.00042 0.095 0.217 1588.2

011025\GR9-009 62.6 489.1 0.747 0.14716 0.00056 1.43054 0.01059 0.07050 0.00045 0.04376 0.00028 �0.750 0.239 885.0

011025\GR9-010 3.0 117.5 0.742 0.03058 0.00047 0.33102 0.01568 0.07850 0.00352 0.00521 0.00021 �5.670 3.620 194.2

011025\GR9-011 18.5 164.2 0.873 0.12939 0.00045 1.19095 0.01175 0.06676 0.00062 0.03995 0.00027 �0.207 0.176 784.4

011025\GR9-012 10.6 91.9 0.819 0.13341 0.00077 1.33666 0.02176 0.07267 0.00111 0.04172 0.00052 �0.209 0.814 807.3

011025\GR9-013 112.7 875.8 0.606 0.14777 0.00039 1.41605 0.00733 0.06950 0.00031 0.04489 0.00023 �0.373 0.102 888.5

011025\GR9-014 54.5 394.1 0.586 0.15909 0.00062 1.59416 0.02065 0.07268 0.00090 0.04788 0.00028 �1.501 0.229 951.7

011025\GR9-015 7.9 71.3 2.300 0.12769 0.00070 1.16814 0.02082 0.06635 0.00112 0.03930 0.00035 �0.197 0.164 774.7

011025\GR9-016 18.3 160.4 0.876 0.13131 0.00051 1.20665 0.01323 0.06665 0.00068 0.04028 0.00026 �0.416 0.121 795.3

011025\GR9-017 278.9 2246.9 0.056 0.14244 0.00035 1.33773 0.00535 0.06811 0.00021 0.04488 0.00029 0.001 0.054 858.5

011025\GR9-018 21.1 306.8 0.446 0.07894 0.00036 0.63033 0.00825 0.05791 0.00071 0.02386 0.00020 �0.374 0.117 489.8

011025\GR9-019 234.1 1334.5 0.498 0.20311 0.00056 2.44943 0.01135 0.08747 0.00032 0.07214 0.00045 1.137 0.947 1192.0

011025\GR9-020 35.6 90.5 2.355 0.45419 0.00250 10.03409 0.10654 0.16023 0.00145 0.12756 0.00073 �0.527 0.581 2413.9

011025\GR9-021 20.3 158.4 0.628 0.14709 0.00063 1.43544 0.01442 0.07078 0.00064 0.04547 0.00036 0.014 0.274 884.6

011025\GR9-022 100.7 279.1 0.402 0.40708 0.00182 7.03597 0.05846 0.12536 0.00088 0.10858 0.00095 �0.401 �1.665 2201.5

011025\GR9-023 138.3 340.3 0.058 0.47491 0.00153 11.63100 0.05368 0.17763 0.00059 0.09261 0.00157 �0.220 1.862 2505.0

011025\GR9-024 21.4 180.0 0.802 0.13730 0.00052 1.35909 0.01311 0.07179 0.00064 0.04308 0.00032 0.188 0.620 829.4

011025\GR9-025 214.9 553.6 1.050 0.45334 0.00133 10.53713 0.04162 0.16858 0.00045 0.12605 0.00060 �0.380 1.811 2410.1

011025\GR9-026 116.6 1736.3 0.085 0.07703 0.00035 0.60189 0.00646 0.05667 0.00055 0.02289 0.00027 �0.071 0.001 478.4

011025\GR9-027 84.8 287.5 0.432 0.33776 0.00092 5.28679 0.02523 0.11352 0.00044 0.09893 0.00057 0.022 �0.156 1875.9

011025\GR9-028 66.4 1281.7 0.023 0.05966 0.00046 0.47482 0.00716 0.05772 0.00075 0.02425 0.00108 0.091 0.449 373.6

011025\GR9-029 310.9 1112.5 0.497 0.32184 0.00072 5.02232 0.01519 0.11318 0.00023 0.09238 0.00033 �0.125 0.408 1798.7

011025\GR9-030 106.5 448.8 0.449 0.27265 0.00090 3.67655 0.01867 0.09780 0.00038 0.08033 0.00035 �0.043 0.183 1554.2

011025\GR9-031 27.6 223.9 0.476 0.14163 0.00078 1.37188 0.01958 0.07025 0.00093 0.04460 0.00053 0.354 0.333 853.9

011025\GR9-032 20.9 168.9 0.828 0.14137 0.00084 1.28819 0.02112 0.06609 0.00101 0.04485 0.00049 0.505 �0.169 852.4

011025\GR9-033 130.2 455.4 0.508 0.32871 0.00104 5.15227 0.02503 0.11368 0.00042 0.09275 0.00049 �0.203 0.214 1832.1

011025\GR9-034 56.7 134.7 0.243 0.48325 0.00187 11.24982 0.06450 0.16884 0.00072 0.13558 0.00099 0.038 0.070 2541.4

011025\GR9-035 114.6 1461.2 0.167 0.09008 0.00041 0.74412 0.00698 0.05991 0.00049 0.02937 0.00038 0.088 0.147 556.0

011025\GR9-036 365.7 911.4 0.662 0.46403 0.00106 10.61519 0.03303 0.16591 0.00035 0.12932 0.00056 �0.003 0.819 2457.3

011025\GR9-038 115.4 910.7 0.505 0.14584 0.00059 1.43520 0.00987 0.07137 0.00040 0.04776 0.00046 0.576 0.375 877.6

011025\GR9-039 90.5 566.5 0.051 0.18514 0.00057 2.16400 0.01338 0.08477 0.00045 0.06325 0.00082 0.105 1.081 1095.0

011025\GR9-040 349.3 1608.9 0.119 0.25369 0.00101 3.72551 0.01900 0.10651 0.00034 0.07427 0.00059 0.014 1.880 1457.5

011025\GR9-041 122.3 305.7 2.055 0.46187 0.00189 10.43810 0.05906 0.16391 0.00064 0.13100 0.00074 1.023 0.661 2447.8

011025\GR9-042 263.7 3773.5 0.663 0.08550 0.00064 1.28896 0.01266 0.10934 0.00070 0.02828 0.00034 0.531 6.672 528.9

011025\GR9-043 89.3 265.8 0.569 0.39906 0.00197 8.86802 0.06576 0.16117 0.00089 0.11578 0.00097 0.303 3.552 2164.7

011025\GR9-044 19.5 84.0 1.159 0.26761 0.00151 3.63849 0.03723 0.09861 0.00084 0.08038 0.00047 0.773 0.446 1528.7

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011025\GR9-045 106.0 360.2 0.159 0.33557 0.00124 5.05376 0.02917 0.10923 0.00048 0.09818 0.00084 0.067 �0.615 1865.3

011025\GR9-047 4.5 1206.5 0.003 0.00429 0.00003 0.02933 0.00074 0.04954 0.00120 0.00641 0.00045 0.190 0.366 27.6

011025\GR9-048 71.2 415.9 0.238 0.20530 0.00155 3.29350 0.04455 0.11635 0.00131 0.07053 0.00127 0.610 4.600 1203.7

011025\GR9-048 45.5 141.2 0.958 0.37252 0.00242 6.79598 0.07407 0.13231 0.00116 0.10119 0.00116 �0.361 0.841 2041.3

011025\GR9-049 57.1 475.5 0.201 0.13789 0.00041 1.30169 0.00900 0.06847 0.00043 0.04136 0.00031 0.022 0.198 832.7

011025\GR9-050 102.5 1903.0 0.219 0.06567 0.00035 0.93563 0.00995 0.10334 0.00095 0.01917 0.00022 �0.171 6.274 410.0

011025\GR9-050 76.4 376.5 0.317 0.23970 0.00290 3.68554 0.06435 0.11152 0.00140 0.07313 0.00059 0.269 2.954 1385.1

011025\GR9-051 18.8 163.7 0.529 0.13156 0.00047 1.18542 0.01291 0.06535 0.00067 0.03932 0.00030 0.068 �0.042 796.7

011025\GR9-052 10.5 153.5 0.742 0.07856 0.00054 0.62211 0.01798 0.05743 0.00161 0.02311 0.00032 �0.326 0.065 487.5

011025\GR9-053 58.8 882.6 0.460 0.07638 0.00040 0.59764 0.00869 0.05675 0.00077 0.02394 0.00026 0.344 0.023 474.5

011025\GR9-054 55.5 820.5 0.061 0.07757 0.00025 0.60436 0.00516 0.05651 0.00045 0.02354 0.00034 �0.004 �0.029 481.6

011025\GR9-055 308.1 961.4 0.915 0.38556 0.00320 8.83605 0.08342 0.16621 0.00075 0.11128 0.00146 0.440 4.879 2102.2

011025\GR9-056 83.4 212.1 0.624 0.45666 0.00131 10.43100 0.04966 0.16566 0.00063 0.12935 0.00063 0.396 1.210 2424.8

011025\GR9-057 246.4 905.3 0.805 0.31427 0.00088 4.90103 0.02056 0.11311 0.00035 0.08837 0.00038 0.107 0.679 1761.7

011025\GR9-058 47.2 367.1 0.909 0.14756 0.00061 1.41538 0.01763 0.06957 0.00082 0.04414 0.00028 0.427 0.116 887.3

011025\GR9-059 197.1 798.9 0.472 0.28287 0.00066 3.84789 0.01485 0.09866 0.00030 0.08371 0.00033 0.321 �0.045 1605.8

011025\GR9-060 0.2 21.3 0.806 0.00888 0.00026 0.12591 0.01404 0.10285 0.01108 0.00292 0.00017 2.196 7.360 57.0

011025\GR9-061 82.5 1003.6 0.012 0.09453 0.00026 0.80581 0.00556 0.06182 0.00039 0.04618 0.00429 0.006 0.294 582.3

011025\GR9-062 60.1 315.4 0.460 0.21888 0.00093 2.54281 0.01930 0.08426 0.00053 0.06711 0.00056 0.268 0.119 1275.9

011025\GR9-063 11.1 165.5 0.872 0.07682 0.00035 0.61569 0.00916 0.05813 0.00082 0.02369 0.00019 0.506 0.184 477.1

011025\GR9-064 22.5 74.3 1.732 0.35002 0.00260 6.05033 0.09244 0.12537 0.00167 0.08755 0.00090 �2.088 0.872 1934.7

011025\GR9-066 64.5 449.5 0.478 0.16455 0.00050 1.62393 0.01020 0.07158 0.00039 0.04994 0.00028 0.326 �0.034 982.0

011025\GR9-067 24.0 60.3 0.827 0.46036 0.00198 10.37908 0.08093 0.16352 0.00106 0.12770 0.00086 0.451 0.691 2441.1

011025\GR9-068 8.6 70.1 0.809 0.14152 0.00070 1.35954 0.02342 0.06967 0.00115 0.04304 0.00038 0.571 0.265 853.3

011025\GR9-069 82.9 500.3 0.467 0.19028 0.00105 2.05993 0.03157 0.07852 0.00112 0.05833 0.00074 0.349 0.177 1122.9

011025\GR9-070 49.5 133.4 0.430 0.43419 0.00139 9.78186 0.05196 0.16340 0.00069 0.12274 0.00070 0.287 2.117 2324.6

011025\GR9-071 147.7 523.3 0.394 0.32497 0.00098 5.10152 0.02768 0.11386 0.00051 0.09386 0.00065 0.274 0.378 1814.0

011025\GR9-072 51.9 795.2 0.051 0.07495 0.00039 0.59432 0.00890 0.05751 0.00081 0.02421 0.00068 0.073 0.143 465.9

011025\GR9-073 36.8 577.8 0.420 0.07321 0.00032 0.58062 0.00847 0.05752 0.00080 0.02256 0.00019 0.266 0.176 455.5

011025\GR9-074 112.5 833.4 0.250 0.16353 0.00070 2.60044 0.02732 0.11533 0.00111 0.04827 0.00053 0.069 5.597 976.4

011025\GR9-075 36.4 554.9 0.067 0.07536 0.00062 0.59195 0.01165 0.05697 0.00102 0.02311 0.00076 0.047 0.069 468.4

011025\GR8-001 33.7 263.9 0.241 0.14648 0.00047 1.37792 0.01138 0.06823 0.00052 0.04476 0.00040 �0.207 �0.023 881.2

011025\GR8-002 67.0 276.2 0.520 0.28082 0.00125 4.09000 0.03496 0.10563 0.00077 0.08054 0.00065 �0.532 0.897 1595.5

011025\GR8-003 17.1 267.2 0.755 0.07355 0.00027 0.56804 0.00732 0.05601 0.00069 0.02206 0.00015 �1.166 �0.014 457.5

011025\GR8-004 35.2 287.4 0.569 0.14035 0.00042 1.30197 0.01038 0.06728 0.00050 0.04281 0.00026 �0.619 �0.001 846.7

011025\GR8-005 67.3 145.1 0.613 0.55114 0.00217 16.89906 0.12025 0.22238 0.00132 0.15203 0.00165 �0.409 3.576 2829.9

011025\GR8-006 121.2 853.6 0.262 0.16271 0.00039 1.58922 0.00735 0.07084 0.00028 0.05013 0.00026 �0.179 �0.081 971.8

011025\GR8-007 64.4 423.5 0.643 0.17536 0.00111 1.90398 0.02626 0.07875 0.00097 0.05561 0.00052 0.143 0.581 1041.6

011025\GR8-008 633.2 2279.9 0.224 0.31961 0.00081 4.93421 0.01842 0.11197 0.00031 0.09024 0.00046 �0.187 0.338 1787.8

011025\GR8-009 299.9 2916.2 0.062 0.12163 0.00101 1.48726 0.01544 0.08869 0.00056 0.04199 0.00068 0.048 3.100 739.9

011025\GR8-009 326.8 1725.1 0.061 0.22126 0.00101 3.00746 0.01819 0.09858 0.00039 0.05978 0.00067 �0.112 1.838 1288.5

011025\GR8-010 39.1 346.8 0.811 0.12932 0.00086 1.15230 0.01999 0.06462 0.00103 0.03925 0.00042 �0.564 �0.082 784.0

011025\GR8-011 43.8 693.2 0.624 0.07248 0.00033 0.56976 0.00656 0.05701 0.00060 0.02319 0.00030 0.003 0.127 451.1

011025\GR8-012 43.5 316.1 0.657 0.15797 0.00056 1.55882 0.01765 0.07157 0.00077 0.04791 0.00038 �0.436 0.120 945.5

011025\GR8-013 724.0 1740.8 0.102 0.47492 0.00096 10.58952 0.02805 0.16172 0.00028 0.12971 0.00058 �0.083 �0.437 2505.1

011025\GR8-014 13.4 190.6 0.448 0.08114 0.00088 0.66706 0.02096 0.05963 0.00176 0.02607 0.00034 0.243 0.285 502.9

011025\GR8-015 10.2 142.7 0.459 0.08271 0.00129 0.71793 0.04323 0.06295 0.00366 0.02760 0.00058 0.322 0.664 512.3

011025\GR8-016 94.0 375.4 0.204 0.29158 0.00188 4.55252 0.05501 0.11324 0.00116 0.09359 0.00084 0.185 1.502 1649.4

011025\GR8-017 45.2 548.5 0.600 0.09474 0.00035 0.80279 0.00916 0.06146 0.00066 0.02993 0.00024 �0.071 0.245 583.5

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Table 1 (continued)


Mount?

Pb*

(ppm)

U

(ppm)

Atomic

Th/U


ratio


ratio


ratio


ratio

F1s.e. %Common206Pb

using 208Pb



age

(Ma)

011025\GR8-018 41.9 181.6 0.686 0.26913 0.00085 4.00687 0.03065 0.10798 0.00075 0.08773 0.00050 0.717 1.581 1536.4

011025\GR8-019 441.1 1113.0 0.103 0.45411 0.00236 9.72054 0.06233 0.15525 0.00058 0.14086 0.00158 0.084 �0.115 2413.5

011025\GR8-024 135.3 1051.7 1.365 0.14799 0.00045 1.45201 0.01064 0.07116 0.00047 0.04356 0.00030 �1.244 0.300 889.7

011025\GR8-020 39.0 598.4 0.092 0.07485 0.00034 0.59655 0.00692 0.05780 0.00062 0.02481 0.00048 0.012 0.180 465.3

011025\GR8-025 101.2 754.8 1.403 0.15406 0.00046 1.51324 0.00922 0.07124 0.00038 0.04514 0.00017 �1.124 0.170 923.7

011025\GR8-026 92.9 636.1 0.581 0.16828 0.00059 1.77444 0.01105 0.07647 0.00039 0.05119 0.00034 �0.139 0.470 1002.7

011025\GR8-027 39.3 249.4 0.712 0.18109 0.00067 1.90709 0.02257 0.07638 0.00086 0.05349 0.00063 �0.343 0.148 1072.9

011025\GR8-028 26.0 96.8 0.616 0.31054 0.00113 4.82929 0.03408 0.11279 0.00068 0.08878 0.00064 �0.312 0.774 1743.4

011025\GR8-029 37.7 557.8 0.973 0.07752 0.00025 0.61140 0.00554 0.05720 0.00049 0.02418 0.00014 �0.254 0.056 481.3

011025\GR8-030 293.4 1525.6 0.032 0.22722 0.00126 3.41900 0.02591 0.10913 0.00056 0.07401 0.00174 0.032 3.017 1319.9

011025\GR8-031 40.4 368.3 0.176 0.12754 0.00053 1.35197 0.01363 0.07688 0.00071 0.05230 0.00066 0.932 1.469 773.8

011025\GR8-032 41.2 343.2 0.887 0.13778 0.00131 1.29101 0.02505 0.06796 0.00115 0.04487 0.00039 0.622 0.139 832.1

011025\GR8-033 88.7 240.0 1.422 0.43347 0.00184 9.82723 0.07265 0.16443 0.00100 0.11836 0.00074 �0.492 2.294 2321.3

011025\GR8-034 40.1 247.5 0.602 0.18588 0.00070 1.96566 0.01746 0.07670 0.00062 0.05616 0.00050 �0.076 0.067 1099.0

011025\GR8-035 134.7 707.7 0.185 0.21895 0.00057 2.59396 0.01249 0.08592 0.00035 0.07667 0.00056 0.410 0.322 1276.4

011025\GR8-036 32.8 7727.4 0.013 0.00488 0.00002 0.03194 0.00049 0.04751 0.00069 0.00201 0.00009 0.056 0.105 31.4

011025\GR8-037 247.1 750.9 0.248 0.39231 0.00291 8.74606 0.08785 0.16169 0.00109 0.11462 0.00366 0.148 3.936 2133.5

011025\GR8-037 166.2 1279.9 0.142 0.16280 0.00149 3.18478 0.05247 0.14188 0.00194 0.06408 0.00146 0.569 9.327 972.3

011025\GR8-038 41.8 112.0 0.992 0.43574 0.00312 9.66323 0.13224 0.16084 0.00188 0.12103 0.00136 0.161 1.676 2331.5

011025\GR8-039 22.2 176.4 0.584 0.14475 0.00092 1.37980 0.01966 0.06913 0.00088 0.04408 0.00070 0.042 0.127 871.5

011025\GR8-040 186.1 1088.9 0.058 0.19634 0.00060 2.16141 0.01606 0.07984 0.00054 0.06018 0.00103 0.017 0.183 1155.6

011025\GR8-041 14.2 174.8 0.405 0.09347 0.00081 0.81497 0.01912 0.06323 0.00138 0.03485 0.00052 1.444 0.489 576.0

011025\GR8-042 112.4 968.9 0.396 0.13334 0.00062 1.24032 0.01157 0.06746 0.00055 0.04382 0.00036 0.575 0.176 806.9

011025\GR8-043 39.7 542.7 0.102 0.08512 0.00114 0.81214 0.01768 0.06920 0.00119 0.06838 0.00162 2.599 1.395 526.6

011025\GR8-044 96.0 369.8 0.604 0.29882 0.00103 4.36153 0.02222 0.10586 0.00040 0.08595 0.00046 �0.011 0.313 1685.5

011025\GR8-045 50.5 405.5 1.591 0.14285 0.00072 1.34010 0.01485 0.06804 0.00067 0.04431 0.00033 0.844 0.036 860.8

011025\GR8-046 48.5 350.4 0.400 0.15907 0.00080 1.59717 0.02740 0.07282 0.00119 0.04944 0.00060 0.222 0.247 951.6

011025\GR8-047 46.5 228.4 0.218 0.24126 0.00236 3.78995 0.07532 0.11393 0.00197 0.07311 0.00184 0.148 3.220 1393.3

011025\GR8-048 76.0 270.1 0.532 0.32666 0.00097 5.45071 0.02860 0.12102 0.00052 0.09596 0.00047 0.214 1.234 1822.2

011025\GR8-049 182.6 413.9 0.604 0.51134 0.00156 13.23747 0.05082 0.18776 0.00044 0.14540 0.00065 0.363 1.022 2662.3

011025\GR8-050 34.9 261.2 1.091 0.15301 0.00086 1.41736 0.01845 0.06718 0.00079 0.04873 0.00047 1.210 �0.299 917.8

011025\GR8-051 29.6 177.8 0.697 0.19199 0.00150 2.13031 0.05518 0.08048 0.00199 0.05670 0.00102 0.165 0.374 1132.1

011025\GR8-052 228.9 949.0 0.468 0.27754 0.00168 3.83034 0.04604 0.10009 0.00104 0.08078 0.00123 0.262 0.310 1579.0

011025\GR8-053 43.0 606.5 0.082 0.08168 0.00039 0.68682 0.00908 0.06099 0.00075 0.02550 0.00052 0.060 0.442 506.1

011025\GR8-054 25.4 162.1 1.088 0.17904 0.00101 1.79707 0.03014 0.07280 0.00115 0.05055 0.00047 �0.659 �0.237 1061.7

011025\GR8-055 212.2 496.4 0.716 0.49947 0.00148 12.95602 0.05765 0.18813 0.00063 0.13550 0.00065 0.140 1.876 2611.5

011025\GR8-057 36.6 616.7 0.151 0.06945 0.00034 0.67943 0.00929 0.07096 0.00091 0.04562 0.00062 2.755 1.923 432.8

011025\GR8-058 3.6 40.1 2.777 0.10370 0.00228 1.05954 0.06429 0.07410 0.00419 0.02876 0.00079 �5.041 1.625 636.1

011025\GR8-059 19.7 207.2 0.480 0.10906 0.00041 0.95887 0.01025 0.06376 0.00064 0.03356 0.00025 0.223 0.239 667.3

011025\GR8-060 22.2 149.8 0.376 0.17000 0.00081 1.67763 0.02411 0.07157 0.00097 0.05030 0.00071 0.090 �0.166 1012.1

011025\GR8-061 162.1 1198.8 0.712 0.15534 0.00071 1.52980 0.01512 0.07142 0.00063 0.04735 0.00050 0.578 0.163 930.8

011025\GR8-062 69.9 1104.5 1.144 0.07269 0.00048 0.57410 0.00889 0.05728 0.00080 0.02280 0.00024 1.130 0.157 452.3

011025\GR8-063 29.5 287.2 0.500 0.11868 0.00110 1.11726 0.02752 0.06828 0.00156 0.04410 0.00063 2.049 0.593 722.9

011025\GR8-064 30.5 377.3 0.125 0.09276 0.00030 0.75051 0.00741 0.05868 0.00055 0.02876 0.00029 0.075 �0.055 571.8

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011025\GR8-065 46.1 359.3 0.857 0.14706 0.00057 1.39500 0.01257 0.06880 0.00056 0.04374 0.00026 0.144 0.033 884.5

011025\GR8-066 109.6 1079.8 1.055 0.11670 0.00035 1.04560 0.01109 0.06498 0.00066 0.03510 0.00061 0.167 0.230 711.5

011025\GR8-067 68.5 168.3 0.680 0.46782 0.00127 10.50697 0.05451 0.16289 0.00072 0.13359 0.00061 0.523 0.163 2474.0

011025\GR8-068 42.8 636.6 0.080 0.07738 0.00061 0.63000 0.00798 0.05905 0.00059 0.03308 0.00090 0.513 0.285 480.5

011025\GR8-069 27.6 199.8 0.904 0.15925 0.00065 1.62271 0.01564 0.07390 0.00065 0.04672 0.00038 0.036 0.375 952.6

011025\GR8-070 45.7 685.2 0.059 0.07652 0.00025 0.59174 0.00561 0.05609 0.00050 0.02380 0.00037 0.031 �0.061 475.3

011025\GR8-071 49.4 175.4 0.325 0.32264 0.00236 4.85128 0.05508 0.10905 0.00095 0.09353 0.00130 0.232 �0.144 1802.6

011025\GR8-072 18.4 198.6 0.783 0.10706 0.00076 0.97487 0.02840 0.06604 0.00187 0.04002 0.00043 3.766 0.561 655.6

011025\GR8-073 18.2 155.4 0.261 0.13469 0.00100 1.23626 0.02138 0.06657 0.00104 0.04346 0.00107 0.443 0.037 814.6

011025\GR8-075 25.4 207.9 0.458 0.14069 0.00054 1.39032 0.01681 0.07167 0.00082 0.04516 0.00043 0.704 0.529 848.6

011025\GR8-21 11.6 91.8 0.636 0.14543 0.00080 1.40781 0.02084 0.07021 0.00097 0.04598 0.00043 0.074 0.242 875.3

011025\GR8-22 26.5 252.7 0.730 0.12057 0.00043 1.09226 0.01041 0.06570 0.00058 0.03797 0.00024 �0.045 0.237 733.8

011025\GR8-23 33.6 242.3 1.154 0.15937 0.00055 1.59912 0.01525 0.07277 0.00065 0.04965 0.00030 0.127 0.234 953.3

011025\GR8-056 230.1 650.2 0.245 0.40882 0.00373 8.11283 0.10040 0.14392 0.00121 0.11845 0.00360 0.061 0.719 2209.5

030820\gR8-2 44.3 540.2 0.536 0.07994 0.00036 0.63480 0.00978 0.05760 0.00085 0.02555 0.00039 �0.077 0.059 495.7

030820\gR8-3 27.3 155.6 0.970 0.15016 0.00121 1.34602 0.02513 0.06501 0.00109 0.05025 0.00129 1.314 �0.496 901.9

030820\gR8-4 142.8 402.3 1.387 0.29288 0.00180 4.00611 0.03332 0.09921 0.00056 0.07923 0.00066 �2.112 �0.314 1655.9

030820\gR8-5 46.2 794.4 0.268 0.05788 0.00044 0.51447 0.01222 0.06446 0.00145 0.03531 0.00053 3.858 1.321 362.7

030820\gR8-7 25.0 302.2 0.660 0.07845 0.00125 0.65605 0.01704 0.06065 0.00124 0.02458 0.00094 �0.282 0.462 486.9

030820\gR8-8 48.1 545.9 0.496 0.09025 0.00122 0.70868 0.02954 0.05695 0.00225 0.02081 0.00047 �2.203 �0.216 557.0

030820\gR8-9 87.8 1325.2 0.022 0.07545 0.00089 0.58668 0.00976 0.05640 0.00066 0.02514 0.00094 0.002 �0.003 468.9

030820\gR8-10 148.3 433.1 0.652 0.32817 0.00266 5.04048 0.05960 0.11140 0.00096 0.09606 0.00117 �0.301 �0.056 1829.5

030820\gR8-11a 56.6 592.1 0.356 0.09880 0.00055 0.84746 0.01026 0.06221 0.00067 0.03054 0.00032 �0.137 0.257 607.4

030820\gR8-12 105.9 831.5 0.544 0.12434 0.00076 1.13996 0.01438 0.06649 0.00074 0.03943 0.00047 0.109 0.253 755.5

030820\gR8-13 142.5 284.9 0.408 0.51027 0.00419 12.58447 0.15698 0.17887 0.00168 0.14779 0.00184 0.150 �0.247 2657.8

030820\gR8-14 81.8 547.0 0.673 0.14125 0.00056 1.31726 0.00984 0.06763 0.00043 0.04375 0.00031 �0.149 0.022 851.8

030820\gR8-15 152.2 279.2 1.147 0.47756 0.00250 10.62830 0.08945 0.16141 0.00106 0.12180 0.00176 �1.437 �0.641 2516.6

030820\gR8-16 136.2 785.1 0.380 0.18317 0.00116 1.96462 0.02923 0.07779 0.00105 0.04181 0.00259 �1.817 0.268 1084.3

030820\gR8-18 36.2 239.1 0.772 0.13977 0.00099 1.35662 0.03253 0.07039 0.00161 0.04379 0.00045 �0.236 0.392 843.4

030820\gR8-19 307.2 840.8 0.179 0.41012 0.00231 9.11848 0.08736 0.16125 0.00125 0.11810 0.00237 �0.018 3.033 2215.5

030820\gR8-20 31.4 428.4 0.220 0.07438 0.00109 0.59608 0.02386 0.05812 0.00216 0.04424 0.00110 2.938 0.228 462.5

030820\gR8-21 115.1 884.7 0.183 0.14132 0.00084 1.36693 0.01660 0.07015 0.00074 0.04454 0.00051 0.009 0.329 852.1

030820\gR8-22 67.5 485.3 0.290 0.14582 0.00068 1.35303 0.01308 0.06730 0.00057 0.04545 0.00048 0.059 �0.121 877.5

030820\gR8-23 22.0 206.4 0.430 0.10538 0.00066 0.96792 0.01570 0.06661 0.00100 0.03956 0.00056 1.342 0.666 645.9

030820\gR8-24 331.4 2575.5 0.010 0.14732 0.00052 1.42533 0.00797 0.07017 0.00031 0.05127 0.00090 0.015 0.195 885.9

030820\gR8-25 21.9 287.9 0.339 0.07877 0.00085 0.62363 0.02288 0.05742 0.00201 0.02437 0.00081 �0.225 0.060 488.8

030820\gR8-26 22.3 199.3 0.729 0.10308 0.00104 0.75507 0.03934 0.05313 0.00271 0.03236 0.00078 �0.177 �0.927 632.4

030820\gR8-28 39.7 367.0 0.661 0.09961 0.00109 0.75222 0.01729 0.05477 0.00111 0.03462 0.00083 0.929 �0.662 612.1

030820\gR8-29 210.8 693.3 0.340 0.31865 0.00195 4.97212 0.03812 0.11317 0.00052 0.09131 0.00073 �0.167 0.526 1783.1

030820\gR8-30 92.8 764.7 0.078 0.13616 0.00132 1.29599 0.01901 0.06903 0.00076 0.04347 0.00077 0.010 0.306 822.9

030820\gR8-31a 111.9 961.6 0.230 0.12300 0.00093 1.16590 0.01394 0.06875 0.00064 0.04746 0.00058 0.756 0.558 747.8

030820\gR8-32 36.5 102.2 0.776 0.32092 0.00545 4.89292 0.23457 0.11058 0.00496 0.11148 0.00331 2.087 0.113 1794.2

030820\gR8-33 2.0 12.1 0.231 0.17390 0.00279 1.63807 0.08674 0.06832 0.00345 0.05332 0.00381 �0.106 �0.653 1033.6

030820\gR8-34 25.3 665.4 0.204 0.03613 0.00035 0.31577 0.00613 0.06339 0.00106 0.03922 0.00050 8.196 1.578 228.8

030820\gR8-35 17.6 116.0 0.564 0.14695 0.00264 1.31515 0.03616 0.06491 0.00135 0.04611 0.00115 �0.112 �0.436 883.8

030820\gR8-36 59.0 365.0 0.494 0.15998 0.00099 1.58277 0.01894 0.07176 0.00073 0.05031 0.00047 0.082 0.095 956.7

030820\gR8-38 258.6 3297.8 0.013 0.08961 0.00061 0.73570 0.00631 0.05954 0.00031 0.03335 0.00094 0.030 0.112 553.3

030820\gR8-39 36.8 257.2 0.500 0.13640 0.00173 1.42486 0.03754 0.07576 0.00175 0.05732 0.00121 2.883 1.134 824.3

030820\gR8-40 20.8 145.1 0.756 0.12913 0.00090 1.10494 0.03032 0.06206 0.00165 0.04429 0.00069 0.925 �0.389 782.9


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237(2005)402–432

413

Table 1 (continued)


Mount?

Pb*

(ppm)

U

(ppm)

Atomic

Th/U


ratio


ratio


ratio


ratio

F1s.e. %Common206Pb

using 208Pb



age

(Ma)

030820\gR8-41 1.7 455.3 0.004 0.00434 0.00013 0.03085 0.00430 0.05159 0.00701 0.02101 0.00429 0.959 0.621 27.9

030820\gR8-42 47.4 319.7 1.875 0.13179 0.00123 1.40053 0.02120 0.07707 0.00092 0.02098 0.00032 �14.907 1.380 798.1

030820\gR8-43 74.9 477.2 0.639 0.15003 0.00086 1.38711 0.01381 0.06705 0.00055 0.04483 0.00035 �0.413 �0.246 901.1

030820\gR8-44 184.6 1260.4 0.157 0.17097 0.00246 3.03135 0.05727 0.12859 0.00158 0.05658 0.00209 0.014 7.217 1017.4

030820\gR8-46 72.0 571.7 0.409 0.12773 0.00060 1.15958 0.01151 0.06584 0.00058 0.04017 0.00027 �0.024 0.100 774.9

030820\gR8-47 48.9 100.1 0.606 0.47708 0.00206 11.01366 0.08365 0.16743 0.00105 0.13593 0.00093 0.036 0.252 2514.5

030820\gR8-48 45.9 276.3 0.471 0.16553 0.00232 1.76461 0.11295 0.07732 0.00483 0.05389 0.00114 1.500 0.645 987.4

030820\gR8-49 59.3 892.4 0.048 0.07505 0.00028 0.57951 0.00455 0.05600 0.00039 0.02248 0.00035 �0.046 �0.043 466.5

030820\gR8-50 102.7 683.4 0.728 0.14030 0.00143 1.32187 0.02982 0.06833 0.00138 0.04305 0.00062 �0.152 0.129 846.4

030303\gan01-i1 Yes 178.9 1314.8 0.034 0.15911 0.00516 2.14326 0.07012 0.09769 0.00042 0.06204 0.00192 0.301 3.379 951.8

030303\gan02-i2 Yes 30.8 331.7 0.085 0.10197 0.00156 1.00448 0.01796 0.07144 0.00066 0.06715 0.00144 1.474 1.335 626.0

030303\gan03-i3 Yes 71.6 572.2 0.356 0.12870 0.00067 1.20792 0.01390 0.06807 0.00070 0.04174 0.00030 0.368 0.352 780.4

030303\gan04-i4 Yes 109.5 418.5 0.136 0.29054 0.00219 4.35330 0.04467 0.10867 0.00075 0.08950 0.00139 0.168 0.955 1644.2

030303\gan05-i5 Yes 1.2 333.6 0.015 0.00401 0.00005 0.02820 0.00150 0.05096 0.00264 0.00274 0.00038 0.279 0.547 25.8

030303\gan07-j1 Yes 78.2 151.5 0.614 0.49606 0.00190 11.06661 0.08031 0.16180 0.00100 0.13527 0.00073 0.003 �1.800 2596.8

030303\gan08-j2 Yes 73.8 150.5 0.386 0.52421 0.00486 15.26464 0.16693 0.21119 0.00123 0.14881 0.00150 0.197 3.755 2717.0

030303\gan09-j5 Yes 34.0 233.1 0.843 0.13287 0.00066 1.27310 0.01242 0.06949 0.00058 0.04077 0.00025 0.106 0.435 804.2

030303\gan10-j6 Yes 178.4 432.2 0.458 0.42704 0.00115 9.20432 0.03665 0.15632 0.00046 0.11348 0.00046 �0.263 1.500 2292.4

030303\gan11-j8 Yes 88.6 865.8 0.404 0.10225 0.00080 0.91367 0.01287 0.06481 0.00076 0.03790 0.00030 1.326 0.506 627.6

030303\gan12-k1 Yes 104.9 1690.5 0.071 0.06972 0.00044 0.51975 0.00874 0.05407 0.00084 0.01780 0.00046 �0.153 �0.181 434.5

030303\gan13-k2 Yes 310.1 548.3 0.300 0.57392 0.00221 14.70765 0.11959 0.18586 0.00133 0.14582 0.00135 �0.197 �4.604 2923.9

030303\gan14-k3 Yes 50.2 223.1 0.673 0.21442 0.00220 2.45561 0.05003 0.08306 0.00146 0.06314 0.00084 �0.078 0.095 1252.3

030303\gan15-k4 Yes 3.9 789.1 0.005 0.00561 0.00009 0.03492 0.00121 0.04516 0.00136 0.00390 0.00075 0.090 �0.194 36.1

030303\gan16-k5 Yes 60.8 713.2 0.338 0.08836 0.00093 0.69166 0.01092 0.05677 0.00067 0.02653 0.00037 0.000 �0.202 545.9

030303\gan17-k6 Yes 173.7 1310.2 0.541 0.13028 0.00205 1.17259 0.02106 0.06528 0.00057 0.03904 0.00030 �0.078 �0.023 789.4

030303\gan17-k6 Yes 2.5 923.5 0.007 0.00313 0.00010 0.02814 0.00152 0.06518 0.00283 0.01550 0.00375 1.675 2.364 20.2

030303\gan18-k7 Yes 6.9 73.4 0.350 0.09687 0.00055 0.78467 0.01649 0.05875 0.00119 0.02965 0.00043 0.037 �0.127 596.1

030303\gan19-k8 Yes 1081.8 2173.1 0.060 0.55059 0.00695 14.21411 0.19352 0.18724 0.00096 0.13468 0.00112 �0.070 �2.107 2827.6

030303\gan19-k8 Yes 106.7 1644.2 0.007 0.07423 0.00117 0.57366 0.01216 0.05605 0.00080 0.02828 0.00121 0.032 �0.022 461.6

030303\gan20-l1 Yes 19.3 123.8 0.574 0.15120 0.00205 1.36480 0.02868 0.06547 0.00105 0.04537 0.00114 �0.111 �0.464 907.7

030303\gan21-l3 Yes 237.9 2159.0 0.007 0.12621 0.00080 1.14108 0.00914 0.06557 0.00032 0.04013 0.00090 0.004 0.100 766.2

030303\gan22-l4 Yes 27.0 333.3 0.429 0.08132 0.00124 0.65077 0.01637 0.05804 0.00116 0.02679 0.00041 0.473 0.087 504.0

030303\gan23-l7 Yes 27.8 188.7 0.864 0.13346 0.00115 1.23707 0.01875 0.06723 0.00084 0.04021 0.00042 �0.103 0.145 807.6

030303\gan25�m1 Yes 123.5 508.3 1.412 0.19108 0.00076 2.10793 0.01405 0.08001 0.00043 0.06101 0.00030 1.913 0.340 1127.2

I.H.Campbell

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237(2005)402–432

414

030303\gan26-m2 Yes 133.9 1099.7 0.451 0.12878 0.00206 2.15063 0.03723 0.12112 0.00081 0.04543 0.00086 1.390 7.285 780.9

030303\gan27-m3 Yes 311.4 698.8 0.422 0.45907 0.00201 10.07189 0.06121 0.15912 0.00067 0.12177 0.00071 �0.214 0.144 2435.4

030303\gan28-m4 Yes 16.0 205.1 0.368 0.07455 0.00315 0.69412 0.03077 0.06753 0.00092 0.04232 0.00040 5.035 1.394 463.5

030303\gan29-m5 Yes 43.1 654.6 0.055 0.07385 0.00030 0.57309 0.00612 0.05628 0.00056 0.03083 0.00096 0.262 0.013 459.3

030303\gan30-m6 Yes 53.4 327.3 0.473 0.16432 0.00044 1.49733 0.01258 0.06609 0.00053 0.04436 0.00037 �0.632 �0.693 980.8

030303\gan31-m7 Yes 263.2 2524.6 0.422 0.10816 0.00105 1.66492 0.01841 0.11164 0.00060 0.04417 0.00045 2.548 6.476 662.1

030303\gan32-m8 Yes 26.9 320.0 0.330 0.08670 0.00059 0.67379 0.01654 0.05636 0.00133 0.02761 0.00046 0.174 �0.219 536.0

030303\gan32-m8 Yes 27.2 9287.4 0.015 0.00335 0.00004 0.02173 0.00101 0.04704 0.00212 0.00089 0.00009 �0.015 0.071 21.6

040709\gR8-401 Yes 9.5 118.4 0.448 0.08035 0.00095 0.63422 0.02227 0.05725 0.00189 0.02530 0.00091 �0.196 0.009 498.2

040709\gR8-401 Yes 116.5 411.5 0.695 0.27115 0.00120 3.77385 0.02164 0.10094 0.00037 0.07801 0.00057 �0.685 0.624 1546.6

040709\gR8-402 Yes 71.6 566.9 0.325 0.13215 0.00131 1.23829 0.01780 0.06796 0.00071 0.03915 0.00048 �0.281 0.263 800.1

040709\gR8-402 Yes 53.6 191.1 0.173 0.30762 0.00434 4.75942 0.09456 0.11221 0.00157 0.09239 0.00242 �0.070 0.806 1729.0

040709\gR8-403 Yes 52.3 159.2 0.622 0.33526 0.00434 6.38089 0.12142 0.13804 0.00193 0.08348 0.00154 �1.662 3.130 1863.8

040709\gR8-406 Yes 17.9 134.8 0.850 0.12140 0.00066 1.12768 0.02082 0.06737 0.00119 0.03627 0.00044 �0.786 0.423 738.6

040709\gR8-408 Yes 35.2 595.5 0.006 0.06797 0.00045 0.56551 0.01583 0.06034 0.00164 0.03577 0.00485 0.064 0.621 423.9

040709\gR8-408 Yes 29.1 186.3 0.340 0.15387 0.00089 1.89276 0.03718 0.08921 0.00167 0.08455 0.00132 3.545 2.426 922.6

040709\gR8-410 Yes 56.5 397.6 0.041 0.16053 0.00116 1.56510 0.04184 0.07071 0.00182 0.05563 0.00174 0.051 �0.045 959.7

040709\gR8-410 Yes 27.0 70.4 1.368 0.32628 0.00236 4.30304 0.07237 0.09565 0.00145 0.07529 0.00088 �4.499 �1.933 1820.3

040709\gR8-411 Yes 15.5 186.1 0.791 0.07695 0.00063 0.63055 0.01803 0.05943 0.00163 0.02318 0.00055 �0.964 0.340 477.9

040709\gR8-413 Yes 33.8 236.8 0.586 0.13886 0.00103 1.33060 0.01750 0.06950 0.00076 0.04208 0.00055 �0.672 0.303 838.2

040709\gR8-414 Yes 116.9 246.7 0.539 0.48715 0.00588 12.40652 0.16572 0.18471 0.00106 0.12248 0.00220 �0.755 2.149 2558.3

040709\gR8-415 Yes 16.8 240.8 0.425 0.07096 0.00040 0.57051 0.00719 0.05831 0.00066 0.02142 0.00023 �0.464 0.314 442.0

040709\gR8-418 Yes 68.5 763.3 0.603 0.08812 0.00215 0.71000 0.01947 0.05844 0.00074 0.02395 0.00038 �1.497 0.006 544.4

040709\gR8-417 Yes 73.6 182.9 0.435 0.43226 0.00214 11.07863 0.07763 0.18588 0.00092 0.12134 0.00096 �0.302 5.430 2315.9

040709\gR8-419 Yes 38.2 140.6 0.186 0.29686 0.00191 4.84467 0.05731 0.11836 0.00118 0.10992 0.00240 0.448 1.979 1675.7

040709\gR8-420 Yes 25.2 188.4 0.726 0.12601 0.00061 1.16124 0.01101 0.06684 0.00055 0.03729 0.00028 �0.860 0.259 765.1

040709\gR8-421 Yes 23.4 132.7 0.874 0.16276 0.00216 1.47884 0.03733 0.06590 0.00141 0.04256 0.00060 �2.224 �0.678 972.1

040709\gR8-436 Yes 38.6 131.7 1.605 0.23084 0.00154 3.15602 0.04136 0.09916 0.00112 0.06743 0.00070 �1.454 1.634 1338.9

040709\gR8-437a Yes 42.6 536.3 0.082 0.08914 0.00064 0.71610 0.00867 0.05826 0.00057 0.02397 0.00066 �0.203 �0.035 550.5

040709\gR8-437a Yes 96.6 1601.3 0.011 0.06906 0.00033 0.53936 0.00506 0.05664 0.00046 0.02078 0.00060 �0.011 0.145 430.5

040709\gR8-440 Yes 9.3 2016.5 0.004 0.00514 0.00019 0.03579 0.00556 0.05051 0.00762 0.04263 0.01884 1.746 0.473 33.1

040709\gR8-440 Yes 51.4 652.8 0.303 0.08313 0.00092 0.66874 0.01121 0.05834 0.00074 0.02299 0.00039 �0.821 0.090 514.8

040709\gR8-444 Yes 36.9 54.3 1.281 0.60636 0.00239 21.19075 0.12842 0.25346 0.00117 0.15511 0.00117 �1.449 4.183 3055.4

040709\gR8-449 Yes 53.7 181.9 0.538 0.30784 0.00185 6.30457 0.05273 0.14853 0.00086 0.09041 0.00096 �0.378 5.605 1730.1

040709\gR8-449 Yes 3.2 552.0 0.015 0.00620 0.00063 0.05285 0.00837 0.06180 0.00750 0.03291 0.01092 2.059 1.880 39.9

040709\gR8-451a Yes 0.8 259.9 0.016 0.00349 0.00012 0.03591 0.00419 0.07456 0.00830 0.01017 0.00237 1.818 3.584 22.5

040709\gR8-451a Yes 414.1 1171.7 0.104 0.44451 0.00663 14.82624 0.22813 0.24191 0.00092 0.14028 0.00135 0.051 13.370 2370.8

040709\gR8-451 Yes 703.8 1569.6 0.173 0.54251 0.00311 19.57305 0.13083 0.26167 0.00090 0.14952 0.00141 �0.122 10.676 2794.0


I.H.Campbell

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andPlaneta

ryScien

ceLetters

237(2005)402–432

415

Table 1 (continued)

Date\analysis ID F1s.e. Uncorr’d207Pb/235U

age

(Ma)


age

(Ma)

F1s.e. 208Pb corr’d206Pb*/238U

age

(Ma)


age

(Ma)

F1s.e. 208Pb corr’d207Pb*/206Pb*

age

(Ma)

F1s.e. y =206/238

age, o =7/6 age,

u =uncor’d,

c =208Pb cor’d

Preferred

age

(Ma)

F1s.e.

011025\GR9-001 17.0 1534.1 17.5 1604.1 18.0 1484.2 17.0 1532.4 17.5 1600.5 18.0 ou 1604.1 18.0

011025\GR9-002 25.1 1883.4 23.0 1842.3 21.5 1925.7 25.1 1892.6 23.2 1859.5 21.8 oc 1859.5 21.8

011025\GR9-003 9.3 827.7 10.6 856.7 10.8 833.7 11.3 889.2 56.8 1056.7 62.8 yu 816.9 9.3

011025\GR9-046 0.8 51.2 2.6 799.2 27.9 36.2 0.8 42.3 2.7 406.5 20.8

011025\GR9-004 9.7 866.8 10.1 876.1 10.1 867.7 9.8 866.4 10.7 874.8 10.7

011025\GR9-005 17.6 1628.1 19.6 1758.7 20.8 1533.4 17.7 1635.8 21.1 1774.2 22.3

011025\GR9-006 7.6 559.0 17.7 654.1 19.4 543.9 7.7 649.7 17.3 1037.5 23.5 yu 535.9 7.6

011025\GR9-006 10.9 848.5 15.6 906.8 15.7 821.8 11.0 768.3 26.0 625.4 22.1 yu 826.3 10.9

011025\GR9-007 17.9 1602.3 18.0 1620.9 18.1 1586.8 17.9 1547.6 18.4 1505.5 17.8 ou 1620.9 18.1

011025\GR9-009 10.2 901.8 10.9 943.2 11.1 891.3 10.4 924.2 15.1 1013.1 16.0

011025\GR9-010 3.6 290.3 12.4 1159.5 33.5 205.7 3.9 440.6 13.6 1982.9 35.4

011025\GR9-011 9.0 796.4 10.3 830.3 10.5 785.9 9.1 781.7 13.3 778.2 13.1 yc 785.9 9.1

011025\GR9-012 9.9 861.8 13.4 1004.8 14.7 808.9 10.0 838.8 17.7 929.7 18.7 yc 808.9 10.0

011025\GR9-013 10.0 895.7 10.3 913.6 10.4 891.6 10.1 897.8 15.7 920.2 15.9

011025\GR9-014 11.0 967.9 13.4 1004.8 13.6 965.2 11.5 984.2 27.6 1053.4 28.6 yu 951.7 11.0

011025\GR9-015 9.4 785.8 13.0 817.6 13.1 776.1 9.6 777.8 20.5 789.1 20.4 yc 776.1 9.6

011025\GR9-016 9.2 803.7 10.7 826.9 10.8 798.5 9.3 798.7 14.4 809.4 14.4 yc 798.5 9.3

011025\GR9-017 9.6 862.2 9.8 871.9 9.8 858.4 9.6 860.1 9.8 865.0 9.7

011025\GR9-018 5.8 496.3 7.5 526.7 7.7 491.6 5.8 506.8 9.4 580.4 10.4 yu 489.8 5.8

011025\GR9-019 13.5 1257.3 14.2 1370.7 15.3 1179.7 13.5 1146.6 20.0 1089.0 19.2

011025\GR9-020 28.8 2437.9 28.6 2458.1 28.3 2424.5 29.5 2423.5 34.0 2435.7 33.6 oc 2435.7 33.6

011025\GR9-021 10.4 903.8 11.6 951.1 11.9 884.5 10.4 892.0 14.5 913.6 14.5 yc 884.5 10.4

011025\GR9-022 25.6 2116.0 24.4 2033.8 23.2 2209.0 25.7 2136.7 25.0 2069.9 23.9 oc 2069.9 23.9

011025\GR9-023 28.4 2575.2 28.7 2630.8 29.1 2509.6 28.4 2587.2 28.8 2648.6 29.3 ou 2630.8 29.1

011025\GR9-024 9.6 871.5 11.1 980.0 12.1 827.9 9.6 843.4 13.5 888.4 13.9 yc 827.9 9.6

011025\GR9-025 27.2 2483.2 27.6 2543.5 28.1 2417.8 30.0 2486.4 42.1 2548.4 42.1 ou 2543.5 28.1

011025\GR9-026 5.7 478.4 6.7 478.9 6.4 478.7 5.7 481.7 6.9 496.1 6.9

011025\GR9-027 21.1 1866.7 20.9 1856.5 20.7 1875.5 21.1 1859.5 21.0 1843.1 20.7 ou 1856.5 20.7

011025\GR9-028 5.0 394.5 6.6 518.8 7.8 373.2 5.0 389.7 6.6 488.4 7.5

011025\GR9-029 20.1 1823.1 20.2 1851.0 20.4 1800.7 20.1 1826.8 20.3 1858.0 20.6 ou 1851.0 20.4

011025\GR9-030 17.7 1566.3 17.7 1582.6 17.7 1554.8 17.7 1563.7 17.8 1577.2 17.8 oc 1577.2 17.8

011025\GR9-031 10.4 877.0 12.8 935.8 13.1 851.1 10.4 856.6 14.6 869.3 14.4 yc 851.1 10.4

011025\GR9-032 10.5 840.5 13.2 809.3 12.3 848.4 10.5 795.6 18.4 651.7 15.5 yu 852.4 10.5

011025\GR9-033 20.8 1844.8 20.7 1859.0 20.7 1835.4 20.8 1858.5 21.2 1884.8 21.3 ou 1859.0 20.7

011025\GR9-034 29.1 2544.1 28.5 2546.2 28.3 2540.6 29.1 2542.2 28.5 2543.3 28.3 oc 2543.3 28.3

011025\GR9-035 6.6 564.8 7.4 600.6 7.6 555.6 6.6 556.2 7.7 559.7 7.5

011025\GR9-036 27.4 2490.0 27.5 2516.8 27.8 2457.4 27.5 2489.9 27.8 2516.6 28.0 ou 2516.8 27.8

011025\GR9-038 10.2 903.7 10.8 968.2 11.2 872.9 10.2 862.3 14.5 833.9 13.9

011025\GR9-039 12.4 1169.6 13.6 1310.3 14.9 1094.0 12.4 1162.3 13.5 1291.8 14.8

011025\GR9-040 16.9 1576.9 17.8 1740.5 19.3 1457.3 16.9 1577.7 17.8 1742.2 19.4

011025\GR9-041 28.2 2474.4 27.7 2496.4 27.7 2427.2 39.0 2450.4 74.4 2459.3 73.4 oc 2459.3 73.4

011025\GR9-042 6.9 840.8 10.8 1788.4 20.4 526.2 8.2 813.4 38.5 1710.3 57.7

011025\GR9-043 25.5 2324.5 26.4 2468.0 27.6 2159.2 25.7 2314.1 28.0 2451.7 29.1

011025\GR9-044 18.5 1558.0 19.0 1598.0 18.9 1518.2 18.5 1524.9 22.3 1527.5 21.8 oc 1527.5 21.8

I.H.Campbell

etal./Earth

andPlaneta

ryScien

ceLetters

237(2005)402–432

416

011025\GR9-045 21.4 1828.4 20.7 1786.6 20.0 1864.3 21.4 1827.3 21.1 1784.5 20.4 ou 1786.6 20.0

011025\GR9-047 0.2 29.4 0.7 174.4 3.9 27.6 0.2 28.4 0.7 102.8 2.5 ou 174.4 3.9

011025\GR9-048 15.6 1479.5 19.4 1901.0 23.0 1197.1 15.7 1445.6 23.2 1831.4 26.5

011025\GR9-048 25.2 2085.2 24.9 2128.9 24.7 2047.6 25.4 2128.7 27.3 2202.9 27.4 ou 2128.9 24.7

011025\GR9-049 9.4 846.5 10.1 882.8 10.4 832.6 9.5 850.4 11.7 895.7 12.1 yu 832.7 9.4

011025\GR9-050 5.0 670.6 9.0 1684.9 20.0 410.7 5.0 679.7 9.3 1714.9 20.5

011025\GR9-050 21.4 1568.2 22.2 1824.3 22.7 1381.8 21.4 1558.1 22.5 1803.9 22.9

011025\GR9-051 9.2 793.8 10.6 785.9 10.3 796.2 9.2 807.4 11.7 832.9 11.9 yu 796.7 9.2

011025\GR9-052 6.3 491.2 12.5 508.5 12.5 489.1 6.3 529.6 14.8 701.5 18.0 yu 487.5 6.3

011025\GR9-053 5.7 475.7 7.6 482.0 7.4 472.9 5.7 472.3 9.8 462.6 9.5 yc 472.9 5.7

011025\GR9-054 5.5 480.0 6.2 472.0 6.0 481.6 5.5 481.7 6.8 481.2 6.7

011025\GR9-055 27.5 2321.2 26.9 2519.9 28.0 2094.4 27.5 2312.0 28.1 2505.6 29.1

011025\GR9-056 27.3 2473.8 27.6 2514.3 27.9 2416.8 27.2 2467.0 27.6 2503.9 27.9 ou 2514.3 27.9

011025\GR9-057 19.9 1802.4 20.1 1849.9 20.5 1760.0 20.1 1828.0 24.1 1898.0 24.7 ou 1849.9 20.5

011025\GR9-058 10.3 895.4 12.3 915.7 12.3 883.7 10.4 914.1 14.7 974.6 15.2 yu 887.3 10.3

011025\GR9-059 18.0 1602.8 17.9 1598.9 17.8 1601.2 17.9 1596.2 18.1 1585.2 17.9 ou 1598.9 17.8

011025\GR9-060 1.8 120.4 12.7 1676.3 90.3 55.8 1.8 104.3 15.9 1423.1 121.0

011025\GR9-061 6.6 600.1 7.3 668.2 8.0 582.3 6.6 600.1 7.4 667.9 8.1 yu 582.3 6.6

011025\GR9-062 14.9 1284.4 15.2 1298.5 15.0 1272.8 17.0 1280.7 55.0 1289.5 54.9 oc 1289.5 54.9

011025\GR9-063 5.6 487.1 7.9 535.0 8.3 474.8 6.0 494.0 27.0 570.6 30.1 yu 477.1 5.6

011025\GR9-064 24.6 1983.1 25.6 2034.0 25.3 1970.2 26.1 2203.5 35.0 2405.6 36.1 ou 2034.0 25.3

011025\GR9-066 11.2 979.5 11.5 974.1 11.3 979.0 11.2 978.2 16.4 970.0 16.2

011025\GR9-067 28.2 2469.2 28.1 2492.3 28.1 2432.0 28.2 2472.6 28.5 2497.6 28.5 ou 2492.3 28.1

011025\GR9-068 10.2 871.7 13.9 918.6 14.2 848.7 10.2 872.8 19.8 922.1 20.4 yu 853.3 10.2

011025\GR9-069 13.6 1135.6 16.3 1159.9 16.1 1119.3 13.6 1123.6 17.9 1127.9 17.6 oc 1127.9 17.6

011025\GR9-070 26.3 2414.4 27.0 2491.1 27.7 2319.0 26.3 2412.3 27.0 2487.8 27.7 ou 2491.1 27.7

011025\GR9-071 20.5 1836.4 20.7 1861.8 20.8 1809.6 20.5 1836.9 20.9 1862.9 21.1 ou 1861.8 20.8

011025\GR9-072 5.6 473.6 7.7 511.0 8.0 465.6 5.6 472.1 7.8 502.7 8.0 yc 465.6 5.6

011025\GR9-073 5.4 464.9 7.5 511.1 7.9 454.3 5.4 468.6 8.6 531.9 9.4 yu 455.5 5.4

011025\GR9-074 11.4 1300.8 16.3 1885.0 22.3 975.8 11.4 1306.0 16.4 1896.3 22.5

011025\GR9-075 6.4 472.1 9.1 490.0 8.8 468.2 6.4 472.9 9.3 494.7 9.1

011025\GR8-001 10.0 879.6 10.8 875.5 10.6 882.9 10.1 879.6 11.9 875.6 11.7 yu 881.2 10.0

011025\GR8-002 18.6 1652.3 19.5 1725.3 19.9 1603.1 18.8 1662.9 20.1 1746.5 20.6 ou 1725.3 19.9

011025\GR8-003 5.3 456.7 6.9 453.2 6.7 462.7 5.4 482.7 8.7 594.1 10.3 yu 457.5 5.3

011025\GR8-004 9.6 846.6 10.4 846.5 10.2 851.6 9.7 846.2 11.7 845.2 11.5 yu 846.7 9.6

011025\GR8-005 32.4 2929.1 32.9 2998.0 33.5 2839.3 32.6 2925.3 33.1 2992.9 33.6 ou 2998.0 33.5

011025\GR8-006 10.9 966.0 11.0 952.8 10.8 973.5 11.0 961.1 15.2 938.0 14.8

011025\GR8-007 13.0 1082.5 15.0 1165.7 15.4 1040.2 13.1 1041.6 22.0 1052.0 21.7

011025\GR8-008 20.1 1808.1 20.1 1831.6 20.3 1790.8 20.1 1813.6 20.3 1842.0 20.5 ou 1831.6 20.3

011025\GR8-009 10.0 925.2 12.0 1397.3 16.1 739.6 10.0 918.2 11.9 1377.2 15.9

011025\GR8-009 15.1 1409.5 16.2 1597.4 17.9 1289.8 15.2 1415.2 16.2 1609.8 18.0

011025\GR8-010 9.9 778.3 12.7 762.3 12.0 788.2 10.3 787.5 27.7 794.7 27.5 yc 788.2 10.3

011025\GR8-011 5.3 457.9 6.6 491.6 6.8 451.1 5.5 444.7 15.1 417.1 14.2 yc 451.1 5.5

011025\GR8-012 10.9 954.0 12.6 973.7 12.7 949.3 10.9 953.7 14.2 972.8 14.3 yc 949.3 10.9

011025\GR8-013 27.9 2487.8 27.5 2473.7 27.3 2506.8 27.9 2489.0 27.5 2475.6 27.3 ou 2473.7 27.3

011025\GR8-014 7.6 518.9 14.0 502.0 10.0 501.7 7.6 501.2 16.3 597.2 16.1

011025\GR8-015 9.5 549.4 26.3 706.3 30.6 510.7 9.5 515.5 29.6 542.2 30.1 yc 510.7 9.5

011025\GR8-016 20.4 1740.6 21.6 1852.0 22.1 1646.7 20.4 1720.6 21.6 1813.3 22.0 oc 1813.3 22.0

011025\GR8-017 6.7 598.4 8.4 384.0 7.5 583.9 6.8 584.3 11.3 592.3 11.3 yc 583.9 6.8


I.H.Campbell

etal./Earth

andPlaneta

ryScien

ceLetters

237(2005)402–432

417

Table 1 (continued)


age

(Ma)


age

(Ma)


age

(Ma)


age

(Ma)


age

(Ma)

F1s.e. y =206/238

age, o =7/6 age,

u =uncor’d,

c =208Pb cor’d

Preferred

age

(Ma)

F1s.e.

011025\GR8-018 17.4 1635.6 19.0 1765.6 20.3 1526.6 17.4 1552.1 19.3 1594.2 19.6 oc 1594.2 19.6

011025\GR8-019 28.5 2408.7 27.1 2404.6 26.7 2411.8 28.5 2401.7 27.2 2393.6 26.7 ou 2404.6 26.7

011025\GR8-024 10.1 910.7 10.9 961.9 11.4 900.2 10.6 969.4 26.2 1139.4 28.9 yu 889.7 10.1

011025\GR8-020 5.5 475.0 6.8 521.9 7.2 465.3 5.5 470.0 8.4 494.7 8.6 yc 465.3 5.5

011025\GR8-025 10.5 935.7 10.9 964.2 11.1 933.4 10.7 999.9 16.3 1154.4 18.0

011025\GR8-026 11.5 1036.1 12.1 1107.4 12.7 1003.9 11.5 1028.4 12.9 1085.6 13.4 yc 1003.9 11.5

011025\GR8-027 12.4 1083.6 14.3 1104.9 14.3 1076.3 12.5 1099.8 19.5 1149.4 19.9 yu 1072.9 12.4

011025\GR8-028 20.0 1790.0 20.6 1844.7 20.9 1748.2 20.0 1799.1 21.2 1862.1 21.7 ou 1844.7 20.9

011025\GR8-029 5.5 484.4 6.4 498.9 6.4 482.5 5.5 481.0 10.5 480.8 10.4 yc 482.5 5.5

011025\GR8-030 16.0 1508.8 17.6 1784.9 20.1 1319.5 16.0 1506.0 17.6 1779.2 20.1

011025\GR8-031 9.0 868.4 11.2 1118.0 13.8 767.1 9.0 803.7 14.1 906.2 15.2 yc 767.1 9.0

011025\GR8-032 11.8 841.7 14.5 867.2 13.7 827.3 11.9 764.3 24.4 592.1 19.8 yu 832.1 11.8

011025\GR8-033 26.8 2418.7 27.5 2501.7 28.1 2331.0 27.3 2451.6 30.4 2552.0 31.1 ou 2501.7 28.1

011025\GR8-034 12.7 1103.8 13.5 1113.2 13.4 1099.8 12.8 1101.7 18.5 1107.5 18.3 yc 1099.8 12.8

011025\GR8-035 14.4 1298.9 14.7 1336.4 15.0 1271.6 14.3 1262.5 14.7 1247.8 14.5 oc 1247.8 14.5

011025\GR8-036 0.4 31.9 0.6 299.2 6.0 31.3 0.4 31.6 0.6 46.5 2.5 yc 31.3 0.4

011025\GR8-037 27.1 2311.9 27.0 2473.4 27.9 2130.9 27.0 2306.7 27.3 2465.2 28.1

011025\GR8-037 13.5 1453.5 20.4 2250.3 27.7 967.2 13.5 1422.4 20.5 2190.7 27.4

011025\GR8-038 29.2 2403.2 29.3 2464.5 29.2 2328.4 29.3 2411.0 30.6 2476.6 30.5 ou 2464.5 29.2

011025\GR8-039 10.9 880.4 12.8 902.6 12.5 871.1 11.0 879.3 17.8 899.2 17.7 yc 871.1 11.0

011025\GR8-040 13.1 1168.7 13.9 1193.0 14.0 1155.4 13.1 1167.2 13.9 1189.1 14.0 oc 1189.1 14.0

011025\GR8-041 7.9 605.2 12.6 396.0 8.0 568.2 7.8 518.4 14.8 301.8 9.1 yu 576.0 7.9

011025\GR8-042 9.6 819.0 10.4 421.3 9.1 802.6 9.6 783.0 19.0 725.4 17.7

011025\GR8-043 8.9 603.7 11.9 431.7 9.3 513.8 8.7 451.6 17.4 143.9 6.3

011025\GR8-044 19.2 1705.1 19.2 1729.3 19.3 1685.6 19.2 1712.9 19.7 1744.6 19.8 ou 1729.3 19.3

011025\GR8-045 10.3 863.3 11.5 869.6 11.2 854.0 11.3 820.6 47.8 724.9 43.8 yu 860.8 10.3

011025\GR8-046 11.4 969.1 15.1 1008.9 15.3 949.6 11.4 957.0 16.2 972.6 16.1 yc 949.6 11.4

011025\GR8-047 19.6 1590.6 23.7 1863.0 25.3 1391.4 19.6 1585.8 24.2 1853.5 25.7

011025\GR8-048 20.6 1892.9 21.3 1971.3 22.0 1818.8 20.7 1884.8 22.6 1956.6 23.2 ou 1971.3 22.0

011025\GR8-049 30.0 2696.7 29.9 2722.6 30.0 2654.4 30.0 2683.5 30.0 2703.5 30.0 ou 2722.6 30.0

011025\GR8-050 11.2 896.3 12.5 843.5 11.5 907.6 11.2 821.3 19.5 587.7 14.9 yu 917.8 11.2

011025\GR8-051 14.9 1158.7 22.0 1208.6 21.9 1130.4 15.1 1171.4 28.6 1241.5 29.1 ou 1208.6 21.9

011025\GR8-052 19.3 1599.1 20.1 1625.8 19.8 1575.3 19.3 1602.2 21.8 1632.1 21.5 ou 1625.8 19.8

011025\GR8-053 6.0 530.9 8.0 638.5 9.1 505.8 6.0 530.4 8.2 636.0 9.3 yc 505.8 6.0

011025\GR8-054 12.9 1044.4 15.9 1008.4 15.0 1068.2 13.2 1134.2 24.7 1253.8 26.0 yu 1061.7 12.9

011025\GR8-055 29.4 2676.5 29.7 2725.9 30.1 2608.5 29.4 2684.8 29.9 2737.9 30.4 ou 2725.9 30.1

011025\GR8-057 5.2 526.4 8.1 442.0 9.5 421.6 5.0 388.3 8.4 191.9 4.4 yc 421.6 5.0

011025\GR8-058 15.0 733.6 32.7 1044.1 38.6 668.1 20.5 1094.1 86.9 2054.9 112.5 yu 636.1 15.0

011025\GR8-059 7.7 682.7 9.2 733.7 9.6 665.9 7.7 682.8 10.0 733.9 10.5 yu 667.3 7.7

011025\GR8-060 12.0 1000.1 14.3 973.9 13.7 1011.3 12.0 1009.9 16.2 1002.5 15.8 yc 1011.3 12.0

011025\GR8-061 11.0 942.4 12.0 969.5 12.0 925.9 10.9 938.4 14.9 957.1 14.9 yu 930.8 11.0

011025\GR8-062 5.8 460.7 7.7 502.1 7.8 447.4 5.9 452.0 17.4 453.9 17.2 yc 447.4 5.9

011025\GR8-063 10.2 761.7 15.6 876.9 16.5 709.2 10.2 636.6 29.6 379.0 19.4 yu 722.9 10.2

011025\GR8-064 6.5 568.5 7.6 555.6 7.3 571.4 6.5 568.3 7.7 554.4 7.4 yc 571.4 6.5

I.H.Campbell

etal./Earth

andPlaneta

ryScien

ceLetters

237(2005)402–432

418

011025\GR8-065 10.2 886.8 11.1 892.6 10.9 883.3 10.3 911.2 14.7 969.9 15.3 yu 884.5 10.2

011025\GR8-066 8.1 726.7 9.7 773.6 10.1 710.4 8.3 755.8 21.9 880.7 24.2 yu 711.5 8.1

011025\GR8-067 27.8 2480.5 27.7 2485.9 27.6 2463.3 27.7 2467.7 27.9 2466.0 27.7 oc 2466.0 27.7

011025\GR8-068 6.4 496.1 7.4 568.5 7.6 478.1 6.4 469.3 7.6 425.5 6.5 yc 478.1 6.4

011025\GR8-069 11.1 979.0 12.4 1038.7 12.8 952.3 11.1 1017.3 15.7 1149.4 17.0 yu 952.6 11.1

011025\GR8-070 5.4 472.0 6.3 456.1 6.0 475.2 5.4 472.0 6.4 456.2 6.0 yc 475.2 5.4

011025\GR8-071 22.9 1793.8 21.9 1783.7 20.9 1799.0 22.9 1793.1 22.5 1782.3 21.5 ou 1783.7 20.9

011025\GR8-072 8.5 691.0 16.5 415.5 9.1 633.0 8.2 485.8 22.2 0.1 0.5 yu 655.6 8.5

011025\GR8-073 10.6 817.2 13.2 824.1 12.7 811.2 10.9 801.7 27.3 770.4 26.1 yu 814.6 10.6

011025\GR8-075 9.8 884.8 12.1 976.4 12.9 843.0 9.8 855.8 14.9 882.5 15.1 yc 843.0 9.8

011025\GR8-21 10.6 892.2 13.2 934.3 13.3 874.7 10.7 860.7 16.3 831.7 15.5 yc 874.7 10.7

011025\GR8-22 8.4 749.6 9.7 796.8 10.0 734.1 8.5 727.4 11.7 714.2 11.4 yc 734.1 8.5

011025\GR8-23 10.9 969.9 12.2 1007.5 12.5 952.2 11.1 929.0 22.6 882.3 21.7 yu 953.3 10.9

011025\GR8-056 29.7 2243.7 27.1 2275.0 26.2 2208.4 29.7 2238.8 27.4 2267.0 26.4 ou 2275.0 26.2

030820\gR8-2 5.9 499.1 8.2 514.1 8.2 496.1 6.2 491.3 27.3 473.8 26.4

030820\gR8-3 12.0 865.8 14.5 774.9 12.5 890.9 12.3 724.7 44.3 246.8 18.5 yu 901.9 12.0

030820\gR8-4 20.3 1635.4 19.2 1609.3 18.3 1687.3 21.2 1753.3 32.5 1843.7 32.9 ou 1609.3 18.3

030820\gR8-5 4.8 421.5 9.4 756.6 14.6 349.6 4.7 216.3 12.9 0.1 0.0

030820\gR8-7 9.2 512.2 11.9 626.7 11.8 488.2 9.3 506.5 26.4 598.2 29.1 yc 488.2 9.3

030820\gR8-8 9.5 544.0 18.5 490.0 16.2 569.0 9.7 667.7 21.4 1022.0 27.4

030820\gR8-9 7.4 468.7 8.1 468.5 6.8 468.9 7.4 468.2 8.4 465.1 7.1

030820\gR8-10 23.9 1826.1 22.4 1822.4 21.3 1834.3 24.0 1816.3 24.5 1803.5 23.4 ou 1822.4 21.3

030820\gR8-11a 7.4 623.3 8.9 681.0 9.2 608.2 7.5 623.0 13.2 679.9 13.9

030820\gR8-12 9.4 772.5 10.9 821.8 11.0 754.7 9.4 750.0 14.9 740.0 14.4 yc 754.7 9.4

030820\gR8-13 34.3 2649.1 31.4 2642.4 30.4 2654.5 34.3 2634.5 31.6 2621.1 30.5 ou 2642.4 30.4

030820\gR8-14 9.9 853.3 10.3 857.2 10.1 852.9 10.1 842.4 21.8 820.8 21.2

030820\gR8-15 29.8 2491.2 28.5 2470.5 27.9 2546.9 32.4 2561.9 42.6 2578.2 42.0 ou 2470.5 27.9

030820\gR8-16 13.5 1103.5 15.7 1141.4 15.6 1102.7 14.1 1209.6 28.0 1414.4 30.3 yu 1084.3 13.5

030820\gR8-18 10.8 870.4 17.0 939.8 17.4 845.3 10.9 844.2 21.1 853.6 20.8 yc 845.3 10.9

030820\gR8-19 26.6 2350.0 27.3 2468.8 28.1 2215.8 26.6 2347.6 27.5 2465.1 28.3 ou 2468.8 28.1

030820\gR8-20 8.3 474.7 16.1 534.0 16.5 449.8 8.1 280.1 20.0 0.1 0.0

030820\gR8-21 10.5 874.8 12.0 932.7 12.1 852.0 10.5 867.0 12.3 907.4 12.3

030820\gR8-22 10.4 868.9 11.1 847.1 10.5 877.0 10.4 861.0 14.0 821.1 13.2

030820\gR8-23 8.1 687.4 11.1 825.6 12.4 637.7 8.1 580.5 19.7 366.9 13.5 yu 645.9 8.1

030820\gR8-24 10.2 899.6 10.4 933.3 10.6 885.8 10.2 898.2 10.5 928.9 10.6

030820\gR8-25 7.4 492.1 15.3 507.4 15.1 489.8 7.5 493.1 19.2 512.7 19.3 yc 489.8 7.5

030820\gR8-26 9.3 571.2 23.6 334.8 15.0 633.5 9.4 554.3 37.0 250.4 19.0 yu 632.4 9.3

030820\gR8-28 9.3 569.5 11.8 343.0 7.0 606.7 9.3 458.1 25.1 0.4 0.2 yu 612.1 9.3

030820\gR8-29 21.8 1814.6 21.0 1850.9 20.7 1785.7 21.8 1817.5 21.4 1856.5 21.2 ou 1850.9 20.7

030820\gR8-30 11.7 844.0 12.5 899.6 11.9 822.8 11.7 839.4 12.6 884.4 11.8

030820\gR8-31a 9.8 784.7 10.8 891.0 11.2 742.5 9.8 718.2 12.9 646.2 11.2

030820\gR8-32 33.1 1801.0 45.0 1808.9 42.8 1762.1 33.1 1619.6 60.2 1442.1 55.3 ou 1808.9 42.8

030820\gR8-33 19.1 985.0 35.1 878.4 31.2 1034.6 19.2 984.3 40.2 876.2 36.1

030820\gR8-34 3.3 278.6 5.6 721.2 11.7 211.7 3.1 �20.0 8.2 0.0 0.0

030820\gR8-35 17.7 852.4 18.4 771.6 14.1 884.7 17.9 827.9 29.4 687.2 24.1 yu 883.8 17.7

030820\gR8-36 11.9 963.5 13.0 978.9 12.5 955.9 11.9 939.8 14.5 906.5 13.6

030820\gR8-38 7.1 559.9 7.2 586.7 6.8 553.1 7.1 557.5 7.2 575.5 6.7

030820\gR8-39 13.4 899.4 18.6 471.0 9.0 802.5 13.1 667.8 28.1 238.4 12.3

030820\gR8-40 10.0 755.7 16.8 389.0 7.4 776.1 10.1 633.3 29.0 165.7 9.7 yu 782.9 10.0


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Table 1 (continued)


age

(Ma)


age

(Ma)


age

(Ma)


age

(Ma)


age

(Ma)

F1s.e. y =206/238

age, o =7/6 age,

u =uncor’d,

c =208Pb cor’d

Preferred

age

(Ma)

F1s.e.

030820\gR8-41 0.9 30.9 4.2 324.5 7.1 27.6 0.9 25.9 4.3 46.5 2.5 yc 27.6 0.9

030820\gR8-42 11.2 889.2 13.3 1123.0 14.8 928.2 15.0 1685.4 34.2 2827.5 43.8

030820\gR8-43 11.0 883.5 11.4 839.6 10.3 904.6 11.1 896.3 14.8 881.1 14.2

030820\gR8-44 17.6 1415.5 21.2 2078.8 25.3 1017.3 17.6 1403.7 21.5 2055.2 25.5

030820\gR8-46 9.2 781.8 10.2 801.1 10.1 775.1 9.2 768.3 11.0 753.1 10.5

030820\gR8-47 29.1 2524.3 28.7 2532.1 28.5 2513.8 29.1 2512.3 28.9 2513.8 28.7 oc 2513.8 28.7

030820\gR8-48 16.8 1032.5 43.0 1129.3 44.3 973.9 18.1 987.3 47.6 998.6 47.0

030820\gR8-49 5.4 464.1 5.9 452.8 5.6 466.7 5.4 465.8 6.1 461.6 5.9

030820\gR8-50 12.3 855.3 16.1 878.5 15.3 847.6 12.4 848.6 25.9 856.3 25.3

030303\gan01-i1 30.5 1162.9 26.0 1580.5 17.7 949.2 30.5 1143.6 26.5 1533.5 18.7

030303\gan02-i2 11.4 706.1 12.0 970.0 12.1 617.3 11.3 612.2 11.3 592.3 8.6

030303\gan03-i3 9.4 804.2 10.9 870.6 11.3 777.8 9.4 780.2 15.1 786.4 14.9

030303\gan04-i4 21.1 1703.5 20.6 1777.2 20.4 1641.8 21.2 1696.0 21.3 1762.4 21.0 ou 1777.2 20.4

030303\gan05-i5 0.4 28.2 1.5 238.2 11.3 25.8 0.4 27.0 1.5 140.7 7.4 yc 25.8 0.4

030303\gan07-j1 29.7 2528.8 28.6 2474.6 27.8 2596.8 29.8 2534.8 29.1 2483.9 28.3 ou 2474.6 27.8

030303\gan08-j2 36.3 2831.9 32.8 2914.7 32.5 2712.7 36.2 2824.3 32.9 2904.3 32.5 ou 2914.7 32.5

030303\gan09-j5 9.6 833.8 10.7 913.2 11.2 803.4 11.2 841.2 54.5 937.9 58.2

030303\gan10-j6 25.7 2358.5 26.2 2416.2 26.7 2297.5 26.6 2379.8 31.7 2449.5 32.1 ou 2416.2 26.7

030303\gan11-j8 8.3 659.0 10.0 767.9 10.5 619.8 8.3 570.5 15.0 377.9 10.4

030303\gan12-k1 5.5 425.0 7.5 374.3 6.4 435.1 5.5 435.3 9.0 435.3 8.7

030303\gan13-k2 33.4 2796.5 31.7 2705.9 30.5 2928.6 33.5 2808.5 31.9 2723.1 30.7 ou 2705.9 30.5

030303\gan14-k3 18.1 1259.1 20.2 1270.6 18.9 1253.2 18.2 1269.1 25.3 1295.1 24.5 ou 1270.6 18.9

030303\gan15-k4 0.7 34.9 1.2 4.4 0.1 36.0 0.7 34.3 1.3 1.3 0.0

030303\gan16-k5 8.2 533.8 8.8 482.9 7.0 545.9 8.2 544.3 12.7 534.3 11.7

030303\gan17-k6 14.6 787.9 13.1 783.6 9.8 790.0 14.6 800.3 17.6 827.3 15.7

030303\gan17-k6 0.7 28.2 1.5 779.8 25.1 19.8 0.7 22.5 2.1 317.1 24.6 yc 19.8 0.7

030303\gan18-k7 7.3 588.1 11.4 558.0 10.6 595.8 7.3 592.5 12.8 577.5 12.3 yc 595.8 7.3

030303\gan19-k8 42.4 2764.1 33.0 2718.1 30.3 2829.2 42.5 2768.1 33.2 2723.8 30.4

030303\gan19-k8 8.6 460.4 9.3 454.9 7.2 461.4 8.6 458.9 9.4 446.3 7.2 yu 461.6 8.6

030303\gan20-l1 15.2 873.9 15.6 789.5 12.4 908.6 15.4 900.3 26.3 875.4 24.5

030303\gan21-l3 9.6 773.0 9.5 792.6 9.1 766.2 9.6 772.8 9.6 791.8 9.1 yc 766.2 9.6

030303\gan22-l4 9.3 509.0 11.5 530.9 10.1 501.7 9.2 482.6 14.5 391.7 11.1

030303\gan23-l7 11.0 817.6 12.4 844.7 11.7 808.4 11.2 832.1 17.9 894.3 18.1 yu 807.6 11.0

030303\gan25�m1 13.1 1151.4 13.5 1197.1 13.7 1107.8 12.9 1019.9 18.1 828.7 15.2 ou 1197.1 13.7

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030303\gan26-m2 14.5 1165.3 17.6 1972.7 22.5 770.8 14.4 1109.0 17.5 1844.0 21.8

030303\gan27-m3 28.2 2441.4 27.4 2446.3 27.2 2439.8 28.3 2456.9 27.7 2470.4 27.5 ou 2446.3 27.2

030303\gan28-m4 19.6 535.3 19.4 854.0 12.2 442.0 18.7 248.8 27.0 0.0 0.0

030303\gan29-m5 5.4 460.0 6.4 463.2 6.3 458.1 5.4 445.0 8.1 377.8 6.9 yu 459.3 5.4

030303\gan30-m6 11.1 929.3 11.4 809.3 9.9 986.6 11.2 991.5 13.8 1000.2 13.8 yc 986.6 11.2

030303\gan31-m7 9.5 995.3 13.0 1826.3 20.6 646.4 9.3 880.4 14.8 1518.8 21.1

030303\gan32-m8 6.9 523.0 11.6 467.0 10.2 535.1 6.9 513.9 13.8 420.2 11.4 yu 536.0 6.9

030303\gan32-m8 0.3 21.8 1.0 46.2 2.1 21.6 0.3 22.0 1.0 65.0 2.9 yu 21.6 0.3

040709\gR8-401 7.9 498.7 14.9 500.9 14.2 499.1 8.0 493.8 25.9 475.5 24.7 yu 498.2 7.9

040709\gR8-401 18.1 1587.2 18.1 1641.5 18.3 1556.1 18.2 1601.8 19.0 1671.6 19.4 ou 1641.5 18.3

040709\gR8-402 11.5 818.1 12.1 867.3 11.3 802.2 12.0 830.5 31.6 909.1 32.9

040709\gR8-402 28.6 1777.8 25.7 1835.5 23.4 1730.1 28.7 1781.5 28.1 1842.6 26.0 ou 1835.5 23.4

040709\gR8-403 29.3 2029.6 27.9 2202.7 27.3 1891.1 29.7 2100.7 29.1 2321.8 29.0

040709\gR8-406 9.0 766.6 13.0 849.1 13.8 744.2 10.3 791.4 49.2 936.1 54.6 yu 738.6 9.0

040709\gR8-408 5.4 455.1 11.4 615.7 14.3 423.7 5.4 451.2 11.7 594.0 14.3 yc 423.7 5.4

040709\gR8-408 11.3 1078.6 17.6 1408.7 21.1 893.1 11.1 755.7 26.8 382.8 15.7

040709\gR8-410 12.4 956.5 19.6 949.3 19.0 959.2 12.4 950.0 19.7 929.2 18.9 yu 959.7 12.4

040709\gR8-410 23.1 1693.9 23.2 1540.9 20.8 1894.6 25.8 1999.2 43.1 2119.0 43.6 oc 2119.0 43.6

040709\gR8-411 6.5 496.4 12.5 582.6 13.7 482.4 12.9 537.6 127.6 784.5 166.5 yu 477.9 6.5

040709\gR8-413 10.9 859.1 12.1 913.4 12.0 843.5 11.0 863.5 14.9 927.6 15.1 yc 843.5 11.0

040709\gR8-414 38.0 2635.7 31.6 2695.6 30.1 2574.4 38.7 2669.4 34.5 2744.3 33.2 ou 2695.6 30.1

040709\gR8-415 5.4 458.3 6.9 541.1 7.6 444.0 5.5 469.0 11.9 599.2 14.2

040709\gR8-418 14.1 544.7 13.0 545.9 8.0 552.3 16.3 618.2 87.1 874.4 109.1 yu 544.4 14.1

040709\gR8-417 27.2 2529.8 28.6 2706.0 30.1 2321.8 27.3 2529.9 28.8 2706.3 30.3

040709\gR8-419 20.7 1792.7 22.1 1931.6 22.9 1669.1 20.7 1744.8 22.2 1840.8 22.6 oc 1840.8 22.6

040709\gR8-420 9.1 782.5 10.0 832.6 10.3 771.3 9.2 811.1 14.6 931.5 15.9 yu 765.1 9.1

040709\gR8-421 16.1 921.8 18.3 803.2 14.8 992.6 16.6 1070.0 25.6 1238.8 26.4 yu 972.1 16.1

040709\gR8-436 16.8 1446.5 18.8 1608.3 19.9 1356.7 17.6 1475.4 35.3 1670.2 37.3

040709\gR8-437a 7.2 548.4 7.9 539.9 7.2 551.5 7.2 557.2 10.4 581.8 10.3 ou 539.9 7.2

040709\gR8-437a 5.1 438.0 5.9 477.2 6.1 430.6 5.1 438.3 5.9 479.1 6.1 ou 477.2 6.1

040709\gR8-440 1.3 35.7 5.5 217.4 29.6 32.5 1.3 25.0 7.4 0.1 0.0 ou 217.4 29.6

040709\gR8-440 7.9 519.9 8.9 542.4 8.0 518.9 7.9 550.8 10.9 691.9 11.9 ou 542.4 8.0

040709\gR8-444 34.9 3147.4 35.1 3206.5 35.6 3091.1 35.5 3178.8 35.8 3245.9 36.3 ou 3206.5 35.6

040709\gR8-449 21.1 2019.1 23.4 2329.1 26.2 1735.8 21.2 2013.5 24.1 2319.7 26.8

040709\gR8-449 4.1 52.3 8.1 667.0 59.8 39.1 4.0 27.0 10.0 0.1 0.0 ou 667.0 59.8

040709\gR8-451a 0.8 35.8 4.1 1056.7 74.0 22.1 0.8 28.2 4.4 587.9 69.0 ou 1056.7 74.0

040709\gR8-451a 39.4 2804.2 34.1 3132.5 34.7 2369.8 39.4 2797.5 34.1 3124.0 34.6

040709\gR8-451 33.4 3070.5 34.4 3256.8 36.0 2796.7 33.4 3069.8 34.4 3255.9 36.0

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Fig. 6. Concordia plot of all of the zircons from the Ganges River dated for this study. Most of the rejected grains lie close to a modern Pb loss

cord from 1850 or 2500 Ma.


to use different values for different thermo-orogenic

events.

The magnitude of DT can be illustrated using the

Indus and Ganges detrital zircon data. Six of 213 or

2.5% of the Ganges zircons and ~7% of the Indus

zircons have U–Pb ages that are younger than 55 Ma,

the start of the Himalayan orogeny. These are primary

first-cycle plutonic zircons that date the age of their

igneous source region. A 25.8F0.6 Ma first-cycle

zircon from the Ganges was double dated and the

He method gave an age of 3.4F0.3 Ma (DT=22

Ma). The Indus zircons also include a population

with ages between 55 and 125 Ma. These zircons

are derived from calc alkaline igneous rocks in the

Kohistan Arc, which formed in the island arc system

that was a precursor to the India–Eurasia collision.

These zircons, which make up 11% of the population,

are here considered part of the Himalayan orogeny

and therefore primary first-cycle zircons. Three zir-

cons belonging to this group were double dated. They

gave U–Pb ages of 111, 110 and 73 Ma, He ages of

4.0, 1.4 and 4.4, for DT s of 107, 108 and 69 respec-

tively. The total percentage of primary first-cycle

zircons in the Indus sand is therefore 18%

(7%+11%). There are no zircons with U–Pb ages of

55 to 125 Ma in the Ganges River.

5.2. Distinguishing between secondary first-cycle and

multi-cycle zircons

The remaining zircons in the Indus and Ganges

rivers have U–Pb ages older than 125 Ma but, with

one exception, He ages that are less than 55 Ma. It is

apparent from their young He ages that these zircons

were derived from the Himalayan Mountains and/or,

in the case of the Indus, the Tibetan Plateau. They are

either secondary first-cycle zircons or multi-cycle zir-

cons. There is no single-grain chronological method

that can be used to distinguish secondary first-cycle

zircons, derived from igneous rocks, from multi-cycle

zircons, derived from sediments. They can, however,

be separated where published geochronology is avail-

able for potential source regions. For example, 42 of

the 213 zircons dated from the Ganges sand gave ages

that correlate with 450–600 Ma Cambro-Ordovician

granites in central Nepal and in the Greater Himalaya

of northern India [14]. Similarly, 15 zircons with ages

~1850 Ma are probably from the mylonitised porphy-

ric granites of the Lesser Himalaya. It is therefore

likely that most of the zircons of these ages in the

Ganges River sand are secondary first-cycle zircons,

although some may have been recycled from Hima-

layan sediments. The breakdown of the Ganges River

Table 2

He and U–Pb ages, and exhumation rates calculated from He ages

for Ganges and Indus river detrital zircons

Sample He age

(Ma)

He exhumation rate

(cm/Myr)

U–Pb core age

(Ma)

Ganges

GAN 5 3.4F0.3 2.1F0.9 25.8F0.6

GAN 7 53F4 0.13F0.06 2547F23

GAN 8 3.7F0.3 1.9F0.9 2712F41

GAN 14 3.0F0.2 2.4F1.1 997F50

GAN 18 26.2F2.1 0.28F0.13 597F7

GAN 23 14.5F1.2 0.5F0.2 808F16

GAN 25 1.5F0.1 4.8F2.2 1108F8

GR-8-5 1.5F0.1 4.8F2.1 2998F34

GR-8-20 3.1F0.3 2.3F1.0 470F17

GR-8-30 2.5F0.2 2.9F1.3 842F11

GR-8-401 3.6F0.3 2.0F0.9 1672F6

GR-8-402 4.9F0.4 1.5F0.7 1842F16

GR-8-403 4.8F0.4 1.5F0.7 2322F14

GR-8-406 3.4F0.3 2.1F0.9 953F53

GR-8-437 4.4F0.4 1.6F0.7 552F4

GR-8-440 3.0F0.2 2.4F1.1 519F6

GR-8-451 4.3F0.3 1.7F0.8 3253F3

Indus

IND 5 3.8F0.3 1.8F0.8 111F1.2

IND 8 3.8F0.3 1.9F0.9 155F1.3

IND 10 1.1F0.1 6.5F2.9 164F2.7

IND 11 15.8F1.3 0.5F0.2 784F5.4

IND 15 0.30F0.02 24F11 1890F20

IND 16 451F35 0.02F0.01 1487F9

IND 20 1.41F0.1 5.1F2.3 110F1.3

IND 24 16.9F1.4 0.4F0.2 209F3

IND 29 4.4F0.4 1.6F0.7 670F90

IND 30 3.9F0.3 1.8F0.8 465F2


zircon types is therefore 3.0% primary first-cycle

zircons, up to 27% secondary first-cycle zircons (if

all 450 to 600 Ma and 1850 Ma grains are secondary

first-cycle zircons) and at least 70% multi-cycle zir-

cons. Similarly, 7% of the Indus zircons have ages

between 480 and 560 Ma and are probably secondary

first-cycle zircons derived from the ~500 Ma grani-

toids in the Lesser and Greater Himalaya. However,

~500 Ma zircons are also an important component in

post-Ordovician Tethyan sediments from Tibet

[21,22], so that some of the zircons of this age in

the Indus River could come from that source. Simi-

larly, most of the ~1850 Ma zircons, which make up

17% of the Indus population, are probably from the

mylonitised porphyritic granites of the Lesser Hima-

laya but some may be recycled from Early Proterozoic

Lesser Himalayan sediments. 1850 Ma zircons have

been recorded from the Early Proterozoic Nawakot

Group but not from younger Cambrian sediments of

the Lesser Himalaya. The Indus River zircons there-

fore comprise 18% primary first-cycle zircons, 0 to

24% secondary first-cycle zircons and 58 to 82%

multi-cycle zircons, depending on the percentage of

the 450 to 600 Ma and 1850 Ma zircons that are

classified as multi-cycle grains.

5.3. Classifying detrital zircons from the Navajo

sandstone

It might be argued that, in the case of the Indus and

Ganges river zircons, the above subdivision of the

detrital zircons into primary first-cycle, secondary

first-cycle and multi-cycle zircons could be made

without He–Pb double dating. However, this is only

possible because it is safe to assume that the bulk of

the sediment load in the Indus and Ganges rivers is

derived from the Himalayan Mountains and Tibetan

Plateau. The assumption of source can rarely be made

with confidence for zircons extracted from old sand-

stones in the geological record, where the source of

the zircons has been removed or largely removed by

erosion.

The power of the He–Pb double dating, to classify

detrital zircons extracted from an old sandstone, can

be illustrated using data from the ~190 Ma Navajo

sandstone, sampled in southwest Utah. Rahl et al. [10]

used this method to determine the provenance of these

zircons and showed that the majority of them were

derived from the Appalachian Mountains. The same

data, which are summarized in Fig. 8, can also be used

to classify the zircons as first or multi-cycle grains.

The four youngest zircons have U–Pb ages between

450 and 600 Ma and He ages that lie between 200 and

500 Ma, only 100 to 250 Myr younger that the

corresponding U–Pb ages for the same grains (see

Fig. 8). These are interpreted to be primary first-

cycle plutonic zircons, derived from granitoids that

formed during one of the four 300 to 600 Ma tectonic

events that produced the Appalachian Mountains.

Zircon fission track ages for Hartford Basin arkoses

and Bronson Hill rocks, both from southern New

England in the north-central Appalachians, vary

between 150 and 240 Ma, and Devonian sediments

from Pennsylvania yield ages between 230 and 350

0

2

4

6

8

10

0 10 20 30 40 50 60

GangesIndus

(U–Th)/He ages

num

ber

+1 Indus at 443+/-35 Ma

Fig. 7. Histograms of the calculated He exhumation ages for zircons from the Indus and Ganges rivers.


Ma, which are consistent with this interpretation

[23,24]. The DT s for the first-cycle Navajo zircons

are greater than those from the Indus and Ganges

sands because the rate of erosion of the mature 300

to 600 Ma Appalachian Mountains is expected to be

slower than that of the younger (b55 Ma) Himalayan

Mountains.

The remaining Navajo sandstone zircons have (U–

Th)/He ages that are at least 500 Myr younger than

their crystallization ages. Those with He ages between

200 and 600 Ma must have come from sediments

from the Appalachian Mountains. Six of the eight

ig. 8. A plot of U–Pb age against (U–Th)/He ages for zircons from the Navajo sandstone. Modified after [10]. DT is the difference between

e ages obtained from the U–Pb and (U–Th)/He systems. DT N300 Myr can be used to distinguish first-cycle zircons from multi-cycle

rains. (U–Th)/He ages of zircons derived from the Appalachian and Grenville orogenies are show by shaded areas. The width of these areas has

een broadened to include ages that are up to 300 Myr younger than the orogenic event that feed the zircons to allow for the likelihood that many

F

th

g

b

of them have He ages that are less than orogenic age due to the time taken

grains, which have He ages between 200 and 600 Ma,

have U–Pb ages between 950 and 1200 Ma, indicating

that they are multi-cycle zircons of Grenville age,

derived from Appalachian sediments. Eriksson et al.

[25,26] have shown that zircons of Grenville age (950

to 1250 Ma) dominate the zircon populations in Appa-

lachian sediments, which is consistent with this inter-

pretation. The remaining two grains have U–Pb ages

of 1350 and 1500 Ma respectively. Zircons with these

ages are also known from Appalachian sediments

[26]. One 1500 Ma and two 2700 Ma zircons, with

the He ages between 800 and 1200 Ma, are interpreted

to exhume deeply buried sediments and intrusions.


to be multi-cycled grains from sediments that last

underwent deep burial (+6 km) and exhumation dur-

ing the Grenville. The ultimate source of the 1500 Ma

zircon is a belt of anorogenic granites of that age that

stretch from California to Labrador. An alternative,

less likely, interpretation for the 1500 Ma zircon and

the two Archaean grains is that they are first-cycle

zircons, and that 850 and 1300 Ma (U–Th)/He ages

are the He exposure ages for anorogenic and Archaean

granitoids in North America respectively. In the

absence of measured He exposure ages for these

rocks, it is impossible to be certain on this point.

Less certain is the provenance of two Archaean zir-

cons that have (U–Th)/He ages of 1300 Ma but their

high DT s indicate that they are multi-cycle grains. If

the Archaean zircons are taken to be multi-cycle

zircons, the breakdown for the Navajo zircons

becomes 23% primary first-cycle and 77% multi-

cycle zircons. All of the zircons in the Navajo sand-

stone are well rounded and, based on their texture,

would be classified as multi-cycle grains. Note that by

using the He–Pb double-dating method, it has been

possible to positively identify the source of all but two

of the individual zircons, including those with a sedi-

mentary source. The U–Pb method can only do this

for first-cycle grains.

6. Provenance

6.1. Constraints from U–Pb ages

The U–Pb ages are of limited value in tracing the

source of the Indus and Ganges zircons. As noted

above, zircons with U–Pb ages younger than 55 Ma

in both the Indus and Ganges rivers are from granitic

rocks, mainly leucogranites, which formed during the

Himalayan orogeny and are found mainly in the

Greater Himalayas (red areas in Fig. 2). Zircons

with ages between 55 and 125 Ma are from the

Kohistan–Ladakh Arc–Transhimalayan Batholith, an

extensive line of pre-collision calc alkaline plutons

north of the Greater and Tethyan Himalayas (Fig. 2).

They are sampled by the Indus River, which flows

west–southwest along the line of the batholiths

before swinging south–southwest near Nanga Parbat

and cutting through the Greater Himalayas. Twelve

percent of the Indus zircons have ages less than 125

Ma and are therefore from the Kohistan–Ladakh

Arc–Transhimalayan Batholith. The Ganges tribu-

taries, however, do not cut through the Greater

Himalaya, which form a drainage divide between

the Ganges and the 55 to 125 Ma calc alkaline

plutons to the north (Figs. 1 and 2). As a conse-

quence, there are no 55 to 125 Ma zircons in the

Ganges sample. Zircons with ages between 450 and

600 Ma are derived from Cambro-Ordovician gran-

ites, which intrude the meta-sediments of both the

Greater and Lesser Himalayas. Examples of intru-

sions of this age are found in Central Nepal [27] and

northern India [28].

A conspicuous feature of the Indus data is a

sharp peak at 1850 Ma, which includes 17% of

the dated zircons. As noted earlier, these are from

the mylonitised porphyric granites of the Lesser

Himalaya. Cumulative probability plots can be

used to isolate the data that belong to this population

and to show that they form a normal distribution

(they lie on a straight line on a cumulative prob-

ability plot). The age of the population is 1852F6

Ma with an MSWD of 1.4. This is as good an

analytical result as can be expected for zircons

extracted from a single igneous rock of that age. It

suggests that the source of these zircons was a

widespread crustal melting event with a duration

of less than 12 Myr. A similar peak in the Ganges

data, which contributes 7% of the zircons, has an

age of 1849F9 Ma. The only known thermal events

that affect large areas of the crust for short periods

are flood basalts. We suggest that the ~1850 Ma

zircons were produced during crustal melting asso-

ciated with a flood basalt.

6.2. Constraints from He ages

The He ages, with the exception of one grain

(IND16), are younger that the onset of the India–

Eurasia collision. If it is assumed that the mean

geothermal gradient is 25 8C/km, with a maximum

uncertainty of F10 8C/km, this requires most of the

eroded material in the Ganges and Indus Rivers to

have been buried to a depth of at least 7F3 km prior

to exhumation during the Himalayan orogeny. It also

precludes the Cenozoic foreland basin sediments of

the Siwalik terrane and material from the Indo-Ganges

plain as an important source of sediment, because they


have not been buried to a sufficient depth during the

last 55 Myr. The exception is grain IND 16, which has

an He age of 451 Ma. It may have originated from one

of these sources. Twenty one or ~75% of the twenty

seven He-dated Indus and Ganges zircons have ages

less than 5 Ma which indicates, perhaps not surpris-

ingly, that the majority of the zircons came from the

regions that were eroding rapidly, with exhumation

rates N1.5 km/Myr. This result places an important

constraint on the source of modern detritus in the

Indus and Ganges rivers. Various authors report zircon

and apatite fission track ages for rocks from the Indus

and Ganges river basins that can be used to constrain

the source of the zircons with He ages b5 Myr. These

ages have been recalculated to exhumation rates,

making the assumption that the closure temperatures

for apatite and zircon are 120 8C and 240 8C, respec-tively, and that the thermal gradient is 25 8C/km, to

facilitate comparison between the different geochro-

nology systems. A zircon with an He age b5 Myr has

an exhumation rate N1.5 km/Myr.

Zircon and apatite fission track dates are available

for samples collected along two Indus tributaries that

drain the southern flank of the Himalayan Mountains,

the Sutlej and Chenab rivers (Fig. 1). Jain et al. [29]

reported exhumation rates N1.0 km/Myr for samples

of Greater Himalayan Crystallines from the Sutlej

River, whereas Kumar et al. [30] found that exhuma-

tion rates are generally less than 0.35 km/Myr for

Greater Himalayan samples collected along the Che-

nab River, to the west of the Sutlej River. Two notable

exceptions are the Kishtwar antiformal window (Fig.

2) and Chisoti Dome (10 km west of the Kishtwar

window), which give exhumation rates of 1.1 and 3.6

km/Myr respectively.

Burbank et al. [31] reported apatite fission track

dates for samples from the Marsyandi River, a tribu-

tary to the Ganges, which cuts both the Lesser and

Greater Himalaya. Ten samples from the Greater

Himalaya gave fission track ages that imply exhuma-

tion rates greater than or equal to 2 to 5 km/Myr,

whereas two apatites from the Lesser Himalayas gave

exhumation rates that are approximately a factor of

five times less.

The most comprehensive study of Himalayan cool-

ing histories is that of Zeitler [32] who measured

fission track cooling ages for zircons (and some apa-

tites) separated from 80 rocks from the Indus basin,

covering an area ca. 350�250 km, mainly to the west

and north of Nanga Parbat (NW corner of Fig. 2).

Ninety percent of the grains have zircon cooling ages

greater than 10 Ma and implied exhumation rates

b1.0 km/Myr. These regions therefore cannot be

the source of the ~75% of zircons in the Indus

River that give young He ages. The remaining 10%

of the zircons are from a restricted area between

Nanga Parbat and Hunza (Fig. 2) where the calculated

exhumation rates vary between 2 and 8 km/Myr, and

average 5 km/Myr. This area, which represents less

than 10% of the area surveyed by Zeitler, is drained

by the Indus and Hunza rivers, which cut rocks of the

Greater Himalaya and Kohistan Arc.

The available fission track dating point to the

Greater Himalaya as a region with exhumation rates

N1.0 km/Myr and therefore an important source of

sediment in the Indus and Ganges rivers. This study

shows that the Kohistan Arc–Ladakh and Gangadese

batholiths are also an important source of zircon in the

Indus River. U–Pb dating shows that 11% of the Indus

zircons are from that source and the grains that have

been double dated give He exhumation ages well in

excess of 1.5 km/Myr. Clift et al. [19], who compared

a compilation of biotite and muscovite 39Ar/40Ar dates

for samples from the western Himalayas with the age

of detrital micas from the Indus, also concluded that

the Greater Himalaya and Kohistan Arc are the most

import source of detritus in that river. Finally, Galy et

al. [33] showed that Sr and Nd isotopes for sediments

from the Bengal Fan are remarkably similar to those

from rocks exposed in the Greater Himalayas, further

suggesting that this is an important source of Indus

detritus.

Harrison et al. [18] argued that the Greater Hima-

laya and Kohistan Arc are important sediment sources

because they are regions of high elevation. However,

the region of highest elevation studied by Zeitler is the

Kaghan River, 50 to 100 km WSW of Nanga Parbat,

where the average elevation is 3000 m. Here zircon

fission track ages vary between 13 and 17 Ma, which

give an average exhumation rate of 0.6 km/Myr,

almost a factor of ten less than for the area between

Nanga Parbat and Hunza (Fig. 2). The difference

between the Kaghan and Nanga Parbat–Hunza

regions is that the Indus and Hunza rivers have

steep valley walls in the area north of Nanga Parbat

whereas the Kaghan river drains a plateau. It therefore


appears that high relief (and associated slope instabil-

ity), and not elevation, is the key factor controlling

exhumation rates and sediment supply.

It is important to remember that quantitative esti-

mates of recycling and provenance, based on He–Pb

double dating of detrital zircons, apply only to the

zircons themselves. Extrapolation of these results to

quantitative estimates of provenance and recycling in

sediments carries with it the implicit assumption that

all source regions have the same mass fraction of

zircon and that zircons are not sorted during transport

in rivers. These two assumptions add additional uncer-

tainty to the estimates.

6.3. Muscovite exhumation rates

Copeland and Harrison [34] report 40Ar/39Ar dates

for detrital muscovites from six samples from an ODP

hole in the Bengal Fan. The estimated age of the host

sediments varies between 2.7 and 16.1 Ma. Twenty

percent of the detrital muscovites, from the five oldest

samples, gave 40Ar/39Ar ages that are younger (by as

much as 4.8 Myr.) than the turbidites from which the

micas were separated, suggesting that there may be a

problem with the estimated age of the host sediment.

As acknowledged by Copeland and Harrison [34],

turbidites have sparse fossils, many of which are trans-

ported, making them notoriously difficult to date and

the ages obtained are often too old. If we confine our

discussion to nine detrital muscovites from the young-

est sample (all of which give 40Ar/39Ar ages that are

older than the estimated age of the host sediment), the40Ar/39Ar ages obtained range between 3.1F1.0 and

17.2F0.9 Ma. If it is assumed that the closure tem-

perature for muscovite is ~350 8C [35] and we again

use a geothermal gradient of 25 8C/km, these ages give

exhumation rates of between 1.0 and 35 km/Myr. The

youngest muscovite yields the 35 km/Myr exhumation

rate, which is an order of magnitude higher than the

next highest exhumation rate and a factor of 8 times

higher than the highest of the Ganges He exhumation

rates (Table 2). If this grain is rejected as an outlier, the

remaining eight grains give exhumation rates that range

between 1.0 and 2.9 km/Myr and have a mean of 1.85

km/Myr. This mean rate is less than the mean rate

calculated from the He ages (2.1 km/Myr), again with

the proviso that muscovite which yields the 35 km/Myr

is excluded.

The exhumation rates for the Indus zircons can be

compared with rates calculated from detrital musco-

vite ages [19] for grains separated from the same

modern Indus River sample that was used in this

study. The ages obtained range between 4 and 38

Ma but most ages lie between 8 and 24 Ma and

there is a pronounced maximum in the ages at 16

Ma. The calculated exhumation rates lie mainly

between 0.6 and 1.8 km/Myr and average is about

0.9 km/Myr. This rate is appreciably lower than the

average rate of 4.8 km/Myr (or 2.5 km/Myr if a single

high value is rejected), calculated from the He ages,

and the range in values is also less. The data are

therefore consistent with the conclusions drawn

from the Ganges He and 40Ar/39Ar dates and are

considered more reliable because they do not involve

the problems associated with estimating the deposi-

tion age of turbidites. The comparison between the

Indus He and 40Ar/39Ar dates provides further support

for the hypothesis that most of the river load comes

from regions that are undergoing anomalously high

erosion rates.

The observation that the average short-term exhu-

mation rate for the sediment load in both the Indus

and Ganges rivers, based on the He dating, is greater

than the average longer term rate, calculated from40Ar/39Ar dates, places an interesting constraint on

the source of the sediment. It implies that the rate of

erosion in the regions that are supplying the bulk of

the sediment to these rivers is well in excess of the

long-term average for the same regions and suggests

that the high exhumation rates are a transient local

feature that last for no more than a few million years

[34]. They are probably from regions that are under-

going faster than normal uplift.

6.4. Significance of the Indus–Ganges results for

U–Pb provenance studies

U–Pb dating of detrital zircons has been widely

used to trace the provenance of sandstone of various

ages in the geological record. The results of this

study show the limitations of this approach. If, 500

Myr into the future, after the Himalayan Mountains

have been reduced to a peneplain, a conventional U–

Pb geochronologist were to date zircons from a sand-

stone that is forming in the Bengal Fan today, he/she

might conclude that 97.5% of the grains were derived


from 500, 900, 1200, 1850 and 2550 Ma igneous or

orogenic events in northern India (see Fig. 4). He/she

would recognize that the 20% of the zircons, with

ages between 480 to 560 Ma, are from the Cambro-

Ordovician granites, but would be unlikely to recog-

nize that they had been uplifted and eroded during

the Himalayan orogeny. The geochronologist could

not be expected to know that these are not primary

first-cycle zircons and, as a consequence, that their

age dates the ultimate source of the zircons and not

their true source. Similarly, it would probably be

concluded that ~80% of the zircons, forming in

today’s Indus cone, came from tectono-magmatic

events in North India and Tibet rather than from

the Himalayan orogeny. A geochronologist, who

did not use the He–Pb double-dating method,

would be unaware that most of the zircons in the

Bengal Fan and Indus Cone came from the Himala-

yan Mountains. Furthermore, the grains are not well

rounded and could not confidently be classified as

multi-cycle grains on the basis of texture. That is,

from a detrital zircons U–Pb age viewpoint, the

Himalaya orogeny is a phantom orogenic event, all

but invisible to the standard U–Pb detrital zircon

provenance study methods. Finally, an U–Pb zircon

geochronologist would recognize that the zircons,

with U–Pb ages between 450 to 600 Ma in the

Navajo sandstone, are first-cycle zircons from the

Appalachian Mountains (Fig. 8). However, six zir-

cons with U–Pb ages of 950 to 1200 Ma, two with

ages of ~1500 Ma and four with ages of ~2700 Ma,

would probably be assigned to the Grenville, anoro-

genic granites and the Archaean respectively. Without

He dates, or other evidence (e.g., Nd isotopes), the

U–Pb geochronologist would be unlikely to recog-

nize that most of these grains are multi-cycle zircons,

with eight of the nine zircons that have U–Pb ages

between 900 and 1500 Ma originating from Appala-

chian sediments and the four Archaean grains from

Grenville sediments. These problems highlight the

difficulties and dangers of using U–Pb zircon dating

in isolation to trace the provenance of detrital zircons.

Note, however, that He dating can only be used to

trace the provenance of zircons if their sedimentary

source has been buried to a depth of over of at least

~7 km, so that they become heated to a temperature

in excess of 180 8C, in the cycle of sedimentation

that is being considered.

7. Why does the India–Eurasia collision produce

little crustal melting?

As can be seen from Fig. 2, Miocene leucogranites

are a minor component of the Himalayas, which

suggests that collision between India and Eurasia

produced little crustal melting. This conclusion is

confirmed by the rarity of zircons with U–Pb ages

b55 Ma in the Indus (7%) and Ganges (3%) rivers.

The Grenville and Pan-African orogenies, and the

cordillera of North and South America, are associated

with abundant granite production and new zircon

growth. The Appalachian orogenies produced much

less zircon that the Grenville [26], but appreciably

more than the Himalayas. Why did the Himalayan

orogeny, which gave rise to the highest mountain

range on modern Earth, produce so little exposed

granite and so little new zircon? There are a number

of possibilities. The India–Eurasia collision may have

been cooler, drier, involved more refractory crust or

crust with a lower Zr content and, as a consequence of

one or more of these factors, produced less crustal

melt and/or new zircon growth. The rocks exposed in

the Himalayas are dominated by meta-sediments,

which makes the last three explanations unlikely,

leaving low crustal temperatures as the most viable

explanation. The cordillera of North and South Amer-

ican are both associated with extensive calc alkaline

magmatism, which must have transferred a consider-

able quantity of heat from the mantle into the crust.

We suggest that the India–Eurasia collision produced

little crustal melting and new zircon growth because it

was not associated with syn-collisional calc alkaline

magmatism.

8. Conclusions

1. The majority of the zircons, from all three of the

samples that have been studied, have been recycled

from earlier sediments: at least 60% and 70% for

the Indus and Ganges river sands respectively and

at least 70% in the case of the Navajo sandstone.

2. Conventional U–Pb geochronology can unambigu-

ously identify only 2.5% of the Ganges zircons and

18% of the Indus zircons as coming from the

Himalayas, and only 23% of the Navajo sandstone

zircons as coming from the Appalachian Moun-


tains. The correct figures, based on the He–Pb

double-dating method, is N95% in the case of the

Himalayan–Ganges and Himalayan–Indus connec-

tions and at least 70% for the Appalachian–Navajo.

3. Approximately 75% of the zircons in the Indus and

Ganges rivers came from areas of rapid erosion

where the exhumation rate is N1.5 km/Myr. The

available fission tack dates suggest that areas with

these high erosion rates represent only a small

fraction of the area drained by the Indus and

Ganges rivers.

4. The areas of high erosion rate are regions of high

relief.

5. The average short-term exhumation rates, calcu-

lated from the zircon He dates, are greater than

the long-term rates, calculated from 40Ar/39Ar det-

rital muscovite dates. This implies that the high

short-term exhumation rates are a transient local

feature.

6. The overwhelming majority of the zircons were

derived from the dominant mountain range on the

continent at the time that the sediments were

deposited, over 95% from the Himalayas in the

case of the Indus and Ganges rivers, and at least

70% from the Appalachian Mountains in the case

of the 190 Ma Navajo sandstone.

7. He–Pb double dating for detrital zircons is superior

to conventional U–Pb as a method for tracing the

source of sediments and can often trace the source

of individual zircons where convention U–Pb dat-

ing cannot.

Acknowledgements

We thank two anonymous reviewers for their con-

structive criticisms of the manuscript. This research

was supported by a grant from the Australian

Research Council.

Appendix A

Zircons were analyzed in four sessions between 2001

and 2004. Zircons selected for conventional U–Pb dat-

ing were mounted in epoxy resin and polished. Optical

photomicrographs were used to map and select least-

fractured and inclusion-free zircons for analysis. Zircons

mounted for the rim-piercing method were mounted on

adhesive tape. All samples were ablated with a pulsed

193 Mm ArF Lambda Physik LPX 1201 UV Excimer

laser with constant 100 mJ energy and a repetition rate

of 5 Hz, using a circular beam 29 or 32 Mm in diameter.

The ablated material from the sample cell was carried

by a mixed Ar–He (with minor H2) carrier gas, through

a flow homogenizer, to an Agilent 7500 ICP-MS.

Counts for 29Si, 91Zr or 89Y, 31P, 177Hf, 206Pb, 207Pb,208Pb, 232Th 235U, 238U and seven rare earth elements

were collected in time-resolved, single point-per-peak

mode. Stoichiometric Hf-corrected Zr was used as the

internal standard for concentration calculations in the

earliest analytical session, and Si for all others. Mea-

sured 235U was used in preference to 238U for the few

zircons with UN2500 ppm to avoid dead-time pro-

blems associated with the measurement of 238U at high

count rates, and 206Pb/238U was calculated from the

measured 206Pb/235U, assuming 238U/235U=137.88.

Much more commonly, 207Pb/235U was calculated

from the measured 207Pb/238U for zircon with

Ub2500 ppm, because 238U was measured with higher

precision than 235U. 204Pb was not measured because

of a high systemic 204Hg blank. The integration time

for the three Pb isotopes, U and Th was 40 ms, and for

all other isotopes it was 10 ms with a total mass sweep

time of 0.385 s. Background was measured for 20 s

with the laser turned off, and the sample measured for

a further 40 s with the laser turned on, giving ~120

mass scans for a penetration depth of ~20 Mm. After

triggering the laser, it took approximately 10 mass

scans to reach a steady signal, so the initial data

were excluded from data reduction.

Depth-dependent inter-element U–Pb and Th/Pb

fractionation (e.g., [36,37]) was corrected by reference

to multiple measurements of standard zircon

TEMORA [38]. Measured 207Pb/206Pb, 206Pb/238U

and 208Pb/232Th ratios in TEMORA were averaged

for each mass sweep down the ablated hole over the

analytical period. These values were used to calculate

the correction factor required to bring the measure

isotopic ratio for each mass sweep back to the

accepted value for the standard. These factors were

then applied to the corresponding mass scan for the

unknowns to simultaneously correct for instrumental

mass bias and depth-dependent elemental and isotopic

fractionation. The results of applying this correction

procedure to a typical U–Pb depth profile are illu-


strated in Fig. 9. Note that the procedure removes

depth-dependent inter-element fractionation. Th/U

fractionation was corrected using either the standard

NIST612 (011025) or NIST610 silicate glass (all other

sessions) [39]. The implicit assumption of this method

is that the depth dependant fractionation factor, at the

depth of each mass sweep, was the same for the

standard as for the unknowns.

The amount of common Pb was determined by

the 208Pb method (the difference between the mea-

sured and expected 208Pb/206Pb, given a preliminary206Pb/238U age and measured Th/U [40]), and the

calculated amount subtracted, assuming a common

Pb composition from the age-dependent Pb model of

Cumming and Richards [41]. Common 206Pb was

less than 1% of total 206Pb in most cases so the

difference between the common Pb corrected and

uncorrected ages was generally small. A common

Pb-corrected age was selected over the uncorrected

one only if it brought the analysis closer to Con-

cordia; it was invoked for one third of the grains that

ultimately met selection criteria (Fig. 6; Table 1).

An age was calculated for each mass sweep down

the ~20 Mm depth profile of the ablation hole, making

it possible to obtain a continuous age profile down the

ablation hole in an age-zoned grain. In this respect

ELA-IPC-MS dating has an advantage over ion probe

dating, which rarely penetrates more than 1 or 2 Mm.

However, the errors in the calculated ages for indivi-

dual mass sweeps were large; only ages averaged over

at least 10 mass scans are reported in this study. The

background corrected fractionation corrected

mass sweep

0.000

0.002

0.004

0.006

0.008

0.010

0.012

50 100 150

example zircon analysis, 98-521

206P

b/23

8U

r.t.

ig. 9. A plot of 206Pb/238U against mass sweep for background

orrected and fractionation corrected data from a typical analysis of

house standard 98–521. Note that the correction procedure used

this study corrects the down-hole 206Pb/238U fractionation (see

xt for details). r.t. (rise time) is the time taken for the signal to

tabilize after the laser is switch on. Data collected during this

eriod are not used in the age calculation.

F

c

in

in

te

s

p

depth regions selected for the reported ages were free

of inclusions (as determined by the analysis) and had

a flat isotope response (uniform age response,

MSWDb twice that expected from counting statistics).

In cases where a distinct core and rim were intersected

(i.e., representing an original magmatic event and a

later overgrowth), one laser ablation might produce

two results. Where this approach has been used to date

the rim and core on the same grain, both analyses have

been given the same sample number in Table 1. Note

this procedure favors accumulation of rim ages,

enhancing the number of analyses with ages b50

Ma in the histogram and still, only 2.9% of the

analysed grains were younger than 55 Ma.

Age uncertainties, which include the uncertainty in

the measurement of the standards, and MSWDs were

calculated for each analysis. The uncertainty in the

standard was derived from the standard deviation of

multiple measurements of the TEMORA zircon,

which was close to 1% for all of 206Pb/238U,207Pb/235U, and 207Pb/206Pb. An analysis was rejected

from interpretation on the basis of the following: (1)

the calculated MSWD for the group of mass sweeps

selected for the date calculation was greater than twice

that expected from counting statistics, or (2) the grain

was deemed to be discordant even after a common Pb

correction was tried. Grains N1100 Ma were deemed

concordant if their 207Pb/206Pb-corrected age, divided

by their 206Pb/238U age (or 208Pb-based common Pb

equivalents if a common Pb correction was applied),

was 1F0.1 including uncertainties. For zircons

b1100 Ma 207Pb/206Pb was replaced by 207Pb/235U.

Both procedures are theoretically equivalent. This

change in concordance criteria is warranted because

for a zircon that is concordant at 100 Ma, a 2%

difference in a measured 206Pb/238U ratio or a207Pb/235U ratio represents about the same difference

in age (2 m.y.) but the same change in 207Pb/206Pb

represents 46 m.y. Contrast this to relative age

changes at 2000 Ma where a 2% difference in206Pb/238U ratio or a 207Pb/206Pb ratio represents

about the same difference in age (34 m.y.) but the

same percent change in 207Pb/235U is significantly less

(17 m.y.). As a consequence, if a percent–age–style

criteria employing only 206Pb/238U-207Pb/206Pb are

used throughout, the percentage of discordant grains

appears to increase in a detrital zircon sample as the

grains become younger. This effect is unlikely to be


real because young grains have less time to become

metamict and are therefore less likely to loose Pb than

ancient grains. The switch in concordance criteria was

set, somewhat arbitrarily, at 1100 Ma, but was selected

to fall in a data-absent part of the age spectrum. In

NIST610 or NIST612 homogenous glass analyses,

generally, the standard deviation in 206Pb/238U was

~1%, and in 207Pb/206Pb, ~0.4%. 206Pb/238U ages are

used for zircon b1100 Ma and 207Pb/206Pb for older

grains. bycQ in Table 1 indicates that common Pb

corrected 206Pb/238U age has been used, byuQ that theuncorrected 206Pb/238U was used, bocQ=207Pb/206Pb-

corrected age and bouQ=207Pb/206Pb uncorrected age.

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