U–Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian Pyrite Belt

ORIGINAL PAPER

U–Pb geochronology and Hf isotope ratios of magmaticzircons from the Iberian Pyrite Belt

D. R. N. Rosa & A. A. Finch & T. Andersen &

C. M. C. Inverno

Received: 26 November 2007 /Accepted: 28 August 2008 / Published online: 30 September 2008# Springer-Verlag 2008

Abstract A geochronology and Hf isotope study, usinglaser ablation-ICP-MS analysis of zircon grains, has beenconducted to date felsic volcanic rocks from the Portuguesesector of the Iberian Pyrite Belt and to establish possiblesources for these rocks. The ages obtained range from theFamennian to the Tournaisian, with the oldest ages reportedin the Belt so far being identified in its southwestern part(Cercal area). Results also indicate that within each area,volcanism may have extended for significant periods oftime. This suggests that caution is needed in interpretingpossible migration trends for the volcanism, as the exactstratigraphic position of the sampled rocks is not alwaysclear. Despite of this, the new data, coupled with previously

reported information, suggests that volcanism migratedwithin the basin from the southwest to the northeast (presentday coordinates). Projection from initial zircon ɛHf valuestowards the depleted mantle evolution curve, via anintermediate reservoir, allows the calculation of Hf protolithmodel ages that are predominantly Meso-Proterozoic. This iscompatible with acid magmas resulting from the fusion ofPhyllite–Quartzite (PQ) Formation metasedimentary rocks,which are beneath the volcanic rocks. This is because zircongrains from one PQ Formation sample provided Late Neo-Proterozoic ages and Paleo-Proterozoic to Late Archean U–Pb ages, and the Hf isotope signatures of these zircons canbe expected to mix during fusion and result in protolithmodel ages that would be intermediate between the two U–Pb age populations, as recorded. Further supporting thissource for the magmas, the distribution of U–Pb ages of(pre-Variscan) inherited zircon grains in the volcanic rocksis very similar to that shown by the detrital zircon grainsfrom a PQ sample.

Introduction

The Iberian Pyrite Belt (IPB) is part of the SouthPortuguese Zone, the southernmost tectonic unit of theIberian Massif and part of the Variscan Orogenic Belt(Julivert et al. 1972). The IPB is interpreted to havedeveloped within a set of pull-apart basins, related to theLate Paleozoic oblique collision of the South Portugueseplate with the Ossa Morena Zone, now located to the north(Silva et al. 1990; Quesada 1991; Tornos et al. 2005;Oliveira et al. 2005). This happened as Pangea amalgam-ated and the Rheic Ocean closed. Syn-volcanic tectonismcaused increased geothermal gradients, and triggered thecirculation and focused discharge of hydrothermal fluids,

Miner Petrol (2009) 95:47–69DOI 10.1007/s00710-008-0022-5

Editorial handling: J. Kosler

D. R. N. Rosa (*) : C. M. C. InvernoINETI-Geological Survey,Estrada da Portela-Zambujal,Alfragide, 2720-866 Amadora, Portugale-mail: [email protected]

D. R. N. RosaGeol. Department, CREMINER-University of Lisbon,Edifício C6, Piso 2, 1749-016 Lisbon, Portugal

A. A. FinchSchool of Geography and Geosciences,University of St. Andrews,St Andrews, Fife, UK

T. AndersenDepartment of Geosciences,University of Oslo,Oslo, Norway

C. M. C. InvernoCREMINER, University of Lisbon,Edifício C6, Piso 2, 1749-016 Lisbon, Portugal

which led to several syngenetic volcanogenic massivesulfide (VMS) deposits. These deposits are of considerableeconomic importance, as they contain significant Cu, Zn,Pb, Sn, Au and Ag. Deposits include Neves-Corvo andAljustrel in Portugal, and Rio Tinto and Aznalcóllar inSpain. The timing, genesis and the evolution of magmasrelated to the formation of these deposits are key inestablishing factors that controlled mineralization and thedevelopment of the IPB basin.

Insights into the timing of the magmatism, its sources andevolution can be obtained through the study of zircon in thevolcanic rocks. This common accessory mineral has a highresistance to high-temperature diffusive re-equilibration andchemical and mechanical weathering. Its low common Pbcontent makes this mineral ideal for U–Pb geochronology,in which the concentrations of U isotopes and daughter Pbisotopes are accurately measured. Additionally, zircon Hfisotope ratios, affected by the decay of 176Lu, provide clueson crustal evolution. Coupled with zircon crystal morphol-ogy, these isotopic systems can therefore be used to provideinsights into magma evolution.

Barrie et al. (2002) reported ID-TIMS U–Pb zircon agesfor felsic rocks from four locations, in both the Portugueseand Spanish sectors of the IPB. Dunning et al. (2002) andNesbitt et al. (1999) reported U–Pb ages for three otherlocations in Spain. While some U–Pb data on volcanicrocks from the IPB are available, they pertain to a limitedset of locations, often with only one sample per location.Additional geochronology constraints are available frompalynomorph and ammonoid studies (Oliveira et al. 2004,2006; Pereira et al. 2007), but these data refer to theinterdigitated metasedimentary rocks and contact relation-ships between these and volcanic rocks are not alwaysclear, either due to tectonic interference or to poor ex-posures. Additional radiometric ages are thus needed inorder to establish migration patterns for the volcanismwithin the IPB basin and to evaluate variations in the age ofthe sources, indicated by inherited grains. Such informationcan aid in the interpretation of the geotectonic evolution ofthe IPB.

In the present article, we report LA-ICPMS U–Pb zircondata for felsic volcanic rocks from several locations withinthe Portuguese sector of the IPB. These results arecompared with published data and palynomorph datingfrom metasedimentary units. Additionally, we report thefirst Hf isotope data from zircons in IPB felsic rocks. TheHf isotope data gathered allow the calculation of protolithmodel ages which are important in the characterization ofpossible sources for the magmas. This is particularlysignificant as these magmas, and associated hydrothermalfluids, are related to the VMS mineralization. To supportthe isotopic evidence, a study of the magmatic zirconmorphologies based on cathodoluminescence imaging has

been also carried out. This study, documenting internalzoning patterns, provides additional insights into the sourceof the magmas and the conditions prevailing during itscrystallization. Finally, reconnaissance U–Pb and Hf iso-tope analyses were made on detrital zircons from a samplefrom the substrate of the IPB, the Phyllite–Quartzite (PQ)Formation, to test this Formation as a possible source forthe felsic magmas. No further data was gathered on the PQformation because a fuller study of this formation will bepublished elsewhere (R. Jorge et al. in prep.).

Geological setting

Three lithostratigraphic groups are recognized in the IPB(Fig. 1), from the oldest to the youngest: (1) the detrital PQFormation, deposited in a shallow marine platform, whosebase is not observed but whose top is Famennian; (2) theVolcanic Siliceous Complex (VSC), hosting the VMSmineralization, of Late Famennian to Middle Visean age;and (3) the turbiditic Flysch Group, marking the filling ofthe basin from the Late Visean to the Serpukhovian(Schermerhorn 1971; Oliveira 1990).

The VSC has normally a thickness of up to 600 m, butcan exceptionally reach thicknesses up to 1300 m (Leistel etal. 1998). Its felsic volcanism was centered in intrabasinalvolcanic edifices that generated voluminous lavas anddomes, and less voluminous but more laterally extensivepyroclastic units. Subsequently, felsic intrusions werelocally emplaced as small cryptodomes and partiallyextrusive cryptodomes (Rosa 2007). Associated with thecoherent felsic facies, there are monomictic breccias.Additionally, resedimented autoclastic facies, coherentmafic facies with uncertain emplacement modes (flowsand/or dykes) and non-volcanic facies, dominated bymudstone, constitute the VSC. Hydrothermal activity takingplace after the volcanism generated the massive sulfidedeposits, as well as abundant manganese-rich and jasperhorizons.

As the result of the Variscan orogeny, the Belt wasaffected by low-grade regional metamorphism, rangingfrom zeolite to greenschist facies (Munhá 1990), and itsstructure is characterized by south- to southwest vergingfolds, corresponding to a thin-skinned foreland fold andthrust belt (Silva et al. 1990).

Geochemistry and petrography of the volcanic rocks

The volcanism of the VSC is bimodal, with a greater volumeof felsic than mafic rocks at current exposure levels (Munhá1983; Mitjavila et al. 1997; Carvalho et al. 1999, Tornos etal. 2005). It is most likely that the majority of intermediate

48 D.R.N. Rosa et al.

compositions reflect silica mobility, with subsequent dispers-al of results on the TAS diagram of Le Maitre et al. (1989),as reported by Rosa et al. (2004). The bimodal nature, withonly minor amounts of intermediate rocks, suggests thatvolcanism was generated in an extensional setting. This iscompatible with the extensional model proposed by Silva etal. (1990), Quesada (1991) and Tornos et al. (2005), amongothers, and is consistent with the geochemistry of the maficrocks (Munhá 1983; Mitjavila et al. 1997; Rosa et al. 2004).The mafic rocks were formed by partial melting of themantle, the degree of which was controlled by the gradualstretching of the lithosphere. This gradual stretchingfavored progressively shallower melting, yielding firstalkaline magmas, with within-plate basalts (WPB) sig-natures, and subsequently tholeiitic magmas, with WPB/mid-oceanic ridge basalts (MORB) signatures. Thesetholeiitic magmas display coupled Th enrichment andNb depletion, which is interpreted as the result of theassimilation of continental crust (Mitjavila et al. 1997;

Rosa et al. 2004). These characteristics are typical ofmagmatism in attenuated continental lithosphere settings,such as the magmatism developed in continental crust bylocal extensional tectonics.

The silicic magmas yielding the felsic rocks were formedby crustal fusion promoted by underplating and theinvasion of the crust by the mafic magmas (Munhá 1983;Mitjavila et al. 1997; Thiéblemont et al. 1998). However,when plotted on the empirically derived tectonic discrim-ination diagrams of Pearce et al. (1984), felsic rocks displayvolcanic arc signatures instead of the extensional settingsuggested by the geochemistry of mafic rocks and by thebimodal distribution of the volcanism. Since the high-fieldstrength elements (HFSE), used in these diagrams, areimmobile, this mismatch has been assigned to anomalouslylow HFSE contents, possibly caused by relatively lowtemperatures of crustal fusion (Rosa et al. 2006). Anoma-lous HFSE concentrations have also been reported in felsicrocks from the Finlayson Lake district, Yukon, Canada and

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Faro

Sines

Huelva

N

Ossa-MorenaZone

4 0 k m

Post-Paleozoic cover

Stitching plutons

Lower Permianoverstepping sequences

Upper Devonian-Lower Carboniferousoverstepping sequences

Syn-orogenic flyschsequencesVolcano-SiliceousComplexPre-orogenicsequences (incl.PQ Fm)

Oceanic sedimentarysequences

Ophiolitic sequences

Ossa-Morena Zone

South Portuguese Terrane:

Iberian Autochthon Terrane:

Pulo do Lobo Terrane:

Atla

ntic

Oce

an

Sevilla

Spa

in

Por

tuga

l

Beja

AB

AL

SB

LS

CE

CA

AJ

CH

Pulo do Lobo

Fig. 1 Simplified geological map of the South Portuguese Zone(modified after Quesada 1991). Location of samples for geochronol-ogy studies: filled diamonds—this study (CE Cercal, CA Caveira, AB

Azinheira de Barros, LS Lousal, AJ Aljustrel, AL Albernoa, SB SerraBranca, CH Chança); open squares—Barrie et al. (2002); opentriangles—Dunning et al. (2002); open circles—Nesbitt et al. (1999)

U–Pb geochronology and Hf isotope ratios of magmatic zircons 49

Bathurst, New Brunswick, Canada, by Piercey et al. (2001)and Lentz (1999), respectively.

For the present study, felsic volcanic rocks from the VSCwere collected at seven locations (Fig. 1, Table 1). AtCercal, Azinheira de Barros, Caveira, Albernoa, SerraBranca and Chança, quartz-feldspar porphyries were sam-pled. Thin section petrography shows that these rock typesare vitrophyric and composed of quartz and plagioclasephenocrysts, the former with frequent embayments. Spo-radically, K-feldspar is also present, as well as biotite, oftenreplaced by chlorite. These phenocrysts are set in a micro-crystalline groundmass, occasionally displaying spheruliticand perlitic textures indicating devitrification from glass.Occasionally, as is the case in one sample from Cercal,flow-banding is apparent. At Serra Branca and Cercal,microporphyries were also sampled. The microporphyrieshave the same mineralogy as the porphyries but thephenocrysts are much smaller and, in Serra Branca, theirgroundmass is altered to hematite. In Aljustrel, threedifferent rock types were sampled; a fine-grained quartz-feldspar-phyric porphyry (“Mine Tuff” unit), a coarse-

grained quartz-feldspar-phyric porphyry (“Lower volcanics”unit) and the megacryst porphyry (Schermerhorn et al.1987, Leitão 1998), with its characteristic large K-feldsparcrystals, interpreted to have formed through metasomatism(Barriga 1983). Regarding the opaque mineralogy, all rocktypes contain accessory amounts of goethite pseudomorphsafter pyrite. Some samples retain trace amounts of pyriteand/or chalcopyrite.

Cathodoluminescence observations show that the quartzphenocrysts of these rocks display a very weak blueluminescence, occasionally revealing zoning. This suggests acomplex crystallization history during quartz growth, withsudden variations in magma composition and/or temperature.

Accessory amounts of zircon are present in the threerock types, as prismatic crystals, approximately 100 μmlong. These crystals exhibit complex oscillatory zoningpatterns, giving evidence for multistage growth histories.The zoning likely reflects slight compositional variations,with brighter zones corresponding to zones with higher U,Th and REE contents (Corfu et al. 2003), or less radiationdamage (Finch et al. 2004), either through lower concen-

Table 1 Sample locations

Sample ID Rock type Location Coordinates

CE1 Microporphyry 1.5 km SW of Cercal. 37°47′45.30′′ N;8°41′9.00′′ WCE2 Spherulitic, flow-banded

microporphyrySão Luís Quarry(1.5 km NW of São Luís).

37°43′38.70′′ N, 8°40′35.50′′ W

CE3 Quartz-feldspar-phyric porphyry 3.5 km ENE of V.N. Milfontes. 37°44′18.30′′ N, 8°44′24.50′′ WCE4 Quartz-feldspar-phyric porphyry V.N. Milfontes-São Luís road cut,

1.5 km west of São Luís.37°43′1.50′′ N, 8°41′2.10′′ W

CAV2 Quartz-feldspar-phyric porphyry Caveira mine; approx. 300 m SSEof the mine inn.

38°7′7.80′′ N, 8°30′2.25′′ W

AZI4 Quartz-feldspar-phyric porphyry South of Monte da Bela Vista,ENE of the Barros beacon.

38°3′14.20′′ N, 8°25′41.30′′ W

SJ1 Megacryst porphyry São João Quarry, Aljustrel 37°53′3.00′′ N, 8°10′49.00′′ WSJ2 Megacryst porphyry São João Quarry, Aljustrel 37°53′3.00′′ N, 8°10′49.00′′ WFEV1 Coarse-grained quartz-feldspar-phyric

porphyryFeitais mine ramp, +135 m, Level 7,Aljustrel

FEV2 Fine-grained quartz-feldspar-phyricporphyry

Sta. Bárbara adit (Feitais sector),−200 m, Aljustrel

CO5 Quartz-feldspar-phyric porphyry Outcrop on the Cobres creek, 7 kmSSE of the village of Albernoa

37°47′59.45′′ N, 7°55′11.80′′ W

IP4 Quartz-feldspar-phyric porphyry IP2 road cut, 2 km south of thevillage of Albernoa.

37°50′40.50′′ N, 7°57′41.36′′ W

SB54 and SB55 Quartz-feldspar-phyric porphyry EN510 road cut, 3 km SSE of villageof Corte de Gafo de Cima.

37°41′49.70′′ N, 7°41′36.00′′ W

SB8-89,7 Microporphyry Drillcore SB8, 89.7 m downhole.Collar 4 km SE of village of Cortede Gafo de Cima.

37°41′42.20′′ N, 7°41′0.50′′ W

CH601 Quartz-feldspar-phyric porphyry Drillcore CH601, 242 m downhole.Chança prospect.

37°42′27.66′′ N, 7°27′8.00′′ W

CH602 Quartz-feldspar-phyric porphyry Drillcore CH602, 175 m downhole.Chança prospect.

34°42′15.12′′ N, 7°26′31.74′′ W

LR23 Phyllite+quartzite Corona creek, near Poço Miguel adit, Lousal. 38°1′48.80′′ N, 8°25′20.20′′ W


trations of radioactive elements, or indicating youngerovergrowths onto inherited (dark) cores. Occasionally thezircon grains contain dark cores that are consistent witholder inherited zones.

The morphology of the zircon grains, based on therecognition of the crystal forms on cathodoluminescenceimages (Belousova et al. 2006), shows that zircon from theIPB volcanic rocks has two different morphological types(Fig. 2). An earlier zircon generation, which is not alwayspresent, has a well developed {100} prism and approxi-mately balanced amounts of the two pyramids, {101} and{211}. These early zircons correspond to subtypes S22 and/

or S23 described by Pupin (1980). This earlier generation istypically overgrown with the more abundant later genera-tion, which has a more developed {110} prism and {101}as the more developed pyramid, with the {211} pyramidbeing subsidiary. These overgrowth zircons correspond tosubtypes S8 and/or S9 of Pupin’s (1980) typologicalclassification. This last subtype can also frequently occurby itself, and does not necessarily constitute overgrowths.These morphological features can be related to changingtemperature and magma composition, on the Pupin (1980)typological classification scheme (Fig. 2c). According toPupin (1980), the relative growth of each prism form

100 200 300 400 500 600 700 800

INDEX A

(301)(101)(101)>>(211)(101)>(211)(101)=(211)(101)<(211)(101)<<(211)(211)

NO PRISM

(110)

(100)<(110)

(100)=(110)

(100)>(110)

(100)

(100)>>(110)

900oC

850oC

800oC

700oC

650oC

600oC

550oC

(100)<<(110)

750oC

PR

ISM

S

PYRAMIDS

B AB1 AB2 AB3 AB4 AB5 A C

IG1

G2

G3L5

R1P1S5S4S3

L4L3L2L1

S2S1

H

Q1

Q2 S6

Q3 S11

S7 S8

S12 S13

S16Q4 S17 S18 S19 S20

S9 S10

S14 S15 P3

P2 R2

R3

P4 R4

R5

FD

P5S25

J5

S24S23S22

J2 J4J3

Q5 S21

E J1

a) b)

c)

50 µm 50 µm

{100}

{110

}

{101}

{211}

Fig. 2 Morphological types ofzircon from a rhyodacite por-phyry from Serra Branca. Cath-odoluminescence imaging andestablished trend on the typo-logical classification scheme ofPupin (1980): (a) illustration ofthe progression of pyramids(sample SB50); (b) illustrationof the change of prisms (sampleSB18); (c) trend on the typo-logical scheme. The imageswere acquired under the follow-ing instrumental settings: accel-erating potential 14 kV, probecurrent 600 μA


encodes the temperature, while the pyramid forms reflectthe alkalinity of the magma. The established trendcorresponds to the cooling of a calc-alkaline to aluminousmagma, of mainly crustal origin. This origin is compatiblewith the model proposed by Munhá (1983), Mitjavila et al.(1997) and Thiéblemont et al. (1998).

Analytical techniques

Sample preparation

Samples for this study were collected at the locationsindicated in Fig. 1, with additional information in Table 1.In addition to the felsic rocks, a sample of the PQFormation was collected, to test if this could be a crediblesource for the acid magmas. Zircon grains were separatedfrom samples using standard density and magnetic proce-dures, at the Department of Geography and Geosciences ofthe University of St Andrews and at the Department ofGeosciences of the University of Oslo. These proceduresincluded the crushing of samples in a jaw crusher, followedby sieving of the <425 μm fractions. The heavy mineralsfrom these fine fractions were then separated usingtetrabromoethane or hetero-polytungstate solution. Subse-quently, the heavy mineral fraction was separated intofractions with different magnetic susceptibilities using aFrantz isodynamic separator. Finally, zircons were hand-picked, under a binocular microscope, from the non-magnetic fraction, mounted in epoxy and polished. Detailedimaging of each grain was carried out using cathodolumi-nescence and backscattered electron imaging. Particularcare was put into identifying inherited cores and limitsbetween different generations of magmatic zircons, toensure that analysis did not straddle different domains.Cathodoluminescence observations and imaging were doneat the University of St Andrews, UK, using a TechnocynMark 4 CL cold cathode equipment attached to an opticalmicroscope. The instrument was set with an acceleratingpotential of 14 kV and probe current of 600 μA.

LA-ICP-MS

Based on the morphological study of magmatic zircons,selected spots were analyzed by LA-ICP-MS. Some zirconsextracted from a PQ Formation sample were also analyzed,for comparison.

U–Pb dating and Lu-Hf isotope analysis were per-formed using a Nu Plasma HR multicollector ICPMS atthe Department of Geosciences, University of Oslo,which is equipped with a U–Pb collector block (fordesign details of the Nu Plasma U–Pb collector block,see Simonetti et al. 2005). A New Wave LUV213 Nd:

YAG laser microprobe was used. Samples were ablated inHe gas (gas flow=1.0 l/min) in an ablation cell similar tothat of Jackson et al. (2004). The He aerosol was mixedwith Ar (gas flow=0.7 l/min) in a teflon mixing cell priorto entry into the plasma. The gas mixture was optimizeddaily for maximum sensitivity. All analyses were made instatic ablation mode, with the laser beam focused inaperture imaging mode with a circular spot geometry. Thisproduced circular, flat-bottomed ablation pits. U–Pb agesand Hf isotope data were determined individually onadjacent spots, using laser operating conditions (seebelow) which secured maximum preservation of theunablated part of the zircon.

U–Pb

U–Pb analyses were made according to analytical protocolsdescribed by Andersen et al. (2007) and Røhr et al. (2008).A single U–Pb measurement included 30 s of on-massbackground measurement, followed by 60 s of ablationwith a stationary beam. Laser conditions for U–Pb analysiswere: beam diameter: 40 μm; pulse frequency: 10 Hz; beamenergy density: ca. 0.06 J/cm2. At these conditions, thedepth-to-diameter ratio of the ablation pit produced duringa 60 s ablation was significantly less than one. Masses 204,206 and 207 were measured in secondary electron multi-pliers, and 238 in the extra high mass Faraday collector ofthe Nu Plasma U–Pb collector block. The geometry of thecollector block does not allow simultaneous measurementof 208Pb and 232Th.

Ion counter counts were converted and reported as voltsby the Nu Plasma time-resolved analysis software. 235Uwas calculated from the signal at mass 238 using a natural238U/235U=137.88.

Mass number 204 was used as a monitor for common204Pb. In an ICPMS analysis, 204Hg originating from theargon supply contaminates mass 204, the observed back-ground counting-rate was ca. 1000 cps (ca. 1.6×10−5 V),and has been stable at that level over a 3-year period. Thecontribution of 204Hg from the plasma was eliminated byon-mass background measurement prior to each analysis.At the low laser energy used, there was no excess ionizationof 204Hg from the gas supply during ablation, so that theon-mass background measurement is representative for theconditions during analysis. Analyses which yielded peak/background ratios at mass 204 of less than 1 + 3RSDB

(where RSDB is the observed relative standard deviation ofthe on-peak background measurement), were considered tohave common lead below the detection limit. Typically, thiswould amount to a background-corrected signal strength onmass 204 of ca. 1.5×10−6 V. For comparison, standards91500 and GJ-1, which are known to contain negligibleamounts of common lead (Wiedenbeck et al. 1995; Jackson


et al. 2004) gave back-ground corrected signal strengths<1.0×10−6 V, i.e. well below the detection limit. In thepresent study, grains showing common lead contents abovethe detection limit were discarded, unless there were nosuitable grains in the whole sample. In contrast, backgroundlevels at masses 206 and 207, which are not influenced byisobaric overlap from contaminating nuclides are ≤300 cps(≤5×10−6 V). Signal strengths on mass 206 for Phanerozoiczircons were typically >(>) 10−4 V, depending on theuranium content of the zircons.

One or two calibration standards were run in duplicate atthe beginning and end of each analytical session, and atregular intervals during sessions. Raw data from the massspectrometer (converted to volts) were corrected forbackground, laser induced elemental fractionation, massdiscrimination and drift in ion counter gains and reduced toU and 206Pb concentrations and U–Pb isotope ratios bycalibration to concordant reference zircons of known age,using protocols adapted from Andersen et al. (2004) andJackson et al. (2004). Standard zircons GJ-01 (609±1Ma; Belousova et al. 2006) and 91500 (1065±1 Ma;Wiedenbeck et al. 1995) were used for calibration. Thecalculations were done off-line, using an in-house inter-active spreadsheet program written in Microsoft Excel/VBA, but with the most computation-heavy routineswritten in C for greater speed of calculation.

Background-corrected signals for mass numbers 204,206, 207 and 238 and the 207Pb/206Pb, 206Pb/238U and207Pb/235U isotope ratios were plotted as traces of observedvoltage and voltage ratios against ablation time, and time-intervals which were homogeneous in isotopic compositionwere interactively selected for integration. To minimize theeffects of laser-induced elemental fractionation, the depth-to-diameter ratio of the ablation pit was kept low, andisotopically homogeneous segments of the time-resolvedtraces were calibrated against the corresponding time-interval for each mass in the reference zircon. Tocompensate for drift in instrument sensitivity and Faradayvs. electron multiplier gain during an analytical session, alinear correlation of signal vs. time was assumed for thereference zircons.

The calibration software incorporates two differentalgorithms for the conversion of background- and drift-corrected signal ratios to isotope and element ratios. Thesimplest approach assumes that the isotopic ratio is a linearfunction of signal ratio and time, i.e.

y ¼ x aþ ctð Þ ð1Þwhere y is the isotopic ratio to be determined, x is theobserved voltage ratio and t the time since the start of theanalytical session. The coefficients a and c are determinedby linear regression of the calibration standards. Thisapproach is equivalent to that incorporated in the commer-

cial software package GLITTER (Van Achterbergh et al.2000). One or more standards can be used to determine aand c by linear regression. At high counting rates on the ioncounters (typically>100,000 cps), effects of dead-time anddeviations from detector linearity affect the results. This canbe compensated by introducing a second-order term in thecalibration equation:

y ¼ x aþ bxþ ctð Þ ð2ÞThe coefficients a, b and c are determined by regression of

data from two or more reference samples. The non-linearcalibration is mainly relevant for zircons with elevated206Pb/238U ratio, i.e. mid-Proterozoic or older zircons. Forthe Phanerozoic zircons analysed in the present study, countingrates are much lower, and Eq. 1 and 2 give indistinguishableresults (Appendix, Table 4). U and 206Pb concentrations werecalculated from observed signals at masses 238 and 206,calibrated to standards according to Eq. 1.

The estimated uncertainties in isotope ratios incorpo-rate error terms from counting statistics on signals andbackgrounds for the relevant masses measured on stan-dards and unknowns, the standard error of the regressionline determined from standards, and the publisheduncertainty of the calibration standards. The terms havebeen propagated through, using standard error propaga-tion algorithms (e.g. Taylor 1997). The correlationcoefficient of errors in the 206Pb/238U and 207Pb/235U(=137.88·207Pb/238U) ratios has been determined from theraw data for each analysis.

The Phanerozoic Temora-2 (TIMS-ID U–Pb age: 416.8±1.3 Ma; Black et al. 2004) and Plešovice (TIMS-ID U–Pbage: 337.1±0.4 Ma; Sláma et al. 2008) reference zirconswere run as unknowns; data obtained during this study aregiven in Appendix (Table 4 and Fig. 9).

Hafnium isotope analysis

For Hf isotope analysis of zircons, masses 172 to 179 weremeasured in Faraday collectors. Ablation conditions were:beam diameter: 55 μm (aperture imaging mode), pulsefrequency: 5 Hz, beam energy density: 1 J/cm2. Eachablation was preceded by a 30 s on-mass backgroundmeasurement. The total Hf signal obtained for zircons withnormal Hf concentration was 1.5–3.0 V. Under theseconditions, 120-150 s of ablation are needed to obtain aninternal precision of ≤±0.000020 (1 SE).

Isotopic ratios were calculated on-line from raw datausing the Nu Plasma time-resolved analysis software.The raw data were corrected for mass discriminationusing an exponential law, the mass discrimination factorfor Hf was determined assuming 179Hf/177Hf=0.7325.The mass discrimination factor for Yb was monitoredfrom the 173Yb/172Yb ratio, but could not be determined


Tab

le2

U–P

bzircon

data

Area

Uppm

206/204

207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/238U*

1SE

Rho

Discordance

207Pb/206Pb

2σ207Pb/235U

2σ206Pb/238U

2σVoltsignal

(backgroundcorrected)

Sam

ple/grain

%Age

(Ma)

Age

(Ma)

Age

(Ma)

206

207

238

Cercal

CE1-zr1

310

2795

0.05484

0.0012

0.44005

0.0040

0.0584

0.0007

0.52

−10.4

406

90370

6366

100.000986

0.000057

0.022475

CE1-zr5

905

5273

0.05447

0.0012

0.44582

0.0052

0.0596

0.0009

0.94

−5391

94374

8373

120.002887

0.000164

0.064541

CE1-zr7

246

3437

0.05407

0.0012

0.43485

0.0048

0.0586

0.0008

0.66

−2.4

374

94367

6367

100.000774

0.000044

0.017553

CE1-zr8

437

3734

0.05403

0.0012

0.44685

0.0046

0.0603

0.0009

0.57

0.9

372

96375

6377

100.001418

0.000080

0.031201

CE1-zr9

200

1631

0.05422

0.0012

0.44510

0.0054

0.0598

0.0009

0.67

−2380

96374

8374

100.000644

0.000036

0.014246

CE1-zr12

666

9664

0.05483

0.0012

0.45319

0.0048

0.0602

0.0009

0.73

−7.6

405

100

380

6377

100.002164

0.000123

0.047519

CE1-zr13

668

7600

0.05493

0.0012

0.44191

0.0047

0.0586

0.0009

0.78

−11

410

94372

6367

100.002112

0.000120

0.047639

CE1-zr14

1372

4854

0.05473

0.0012

0.45338

0.0047

0.0604

0.0009

0.74

−6.4

401

96380

6378

100.004469

0.000253

0.097901

CE1-zr15

773

19553

0.05395

0.0012

0.44226

0.0050

0.0597

0.0009

0.87

1369

98372

6374

120.002495

0.000139

0.055178

CE1-zr16

451

8647

0.05408

0.0012

0.44413

0.0060

0.0598

0.0010

0.95

−0.3

374

94373

8375

120.001454

0.000081

0.032144

CE1-zr17

399

2842

0.05487

0.0013

0.44249

0.0046

0.0588

0.0009

0.71

−10.2

407

104

372

6368

100.001291

0.000073

0.029046

CE1-zr19

371

4909

0.05396

0.0012

0.44646

0.0049

0.0603

0.0009

0.81

1.7

369

96375

6377

100.001210

0.000067

0.026489

CE1-zr20

784

5971

0.05410

0.0012

0.45185

0.0049

0.0609

0.0009

0.81

1.1

375

96379

6381

120.002583

0.000144

0.055964

CE1-zr21

654

5996

0.05500

0.0012

0.45104

0.0048

0.0598

0.0009

0.71

−9.9

412

94378

6374

100.002117

0.000119

0.046643

CE1-zr24

522

6318

0.05494

0.0012

0.45582

0.0050

0.0604

0.0009

0.51

−8.3

410

94381

6378

120.001710

0.000096

0.037214

CE1-zr10

121

8458

0.12612

0.0045

5.72535

0.2329

0.3508

0.0118

0.83

−11.8

2045

120

1935

701938

112

0.002524

0.000341

0.008609

CE1-zr11

470

3738

0.05393

0.0012

0.44136

0.0046

0.0596

0.0009

0.58

1368

96371

6373

100.001511

0.000084

0.033512

CE2-zr11

410

2799

0.05424

0.0002

0.43348

0.0051

0.0580

0.0007

0.46

−4.8

381

14366

8363

80.001469

0.000085

0.031219

CE2-zr12

442

5023

0.05430

0.0002

0.44238

0.0052

0.0591

0.0007

0.48

−3.6

383

14372

8370

80.001605

0.000093

0.033534

CE2-zr13

548

6351

0.05396

0.0002

0.43322

0.0052

0.0582

0.0007

0.55

−1.2

369

14365

8365

80.001965

0.000113

0.041657

CE2-zr14

402

4203

0.05351

0.0002

0.43138

0.0053

0.0585

0.0007

0.64

4.6

351

14364

8366

80.001441

0.000082

0.030458

CE2-zr15

415

4406

0.05386

0.0002

0.43233

0.0053

0.0582

0.0007

0.50

−0.1

365

16365

8365

80.001483

0.000085

0.031470

CE2-zr16

386

77084

0.05388

0.0002

0.43787

0.0051

0.0590

0.0007

0.40

0.8

366

14369

8369

80.001378

0.000079

0.029007

CE2-zr17

506

4858

0.05436

0.0002

0.44220

0.0055

0.0590

0.0007

0.58

−4.3

386

14372

8370

80.001779

0.000103

0.037659

CE2-zr2

384

2986

0.05450

0.0002

0.43564

0.0050

0.0580

0.0007

.−7

.5392

14367

8363

80.001436

0.000083

0.030010

CE2-zr20

752

7648

0.05432

0.0002

0.44940

0.0055

0.0600

0.0007

0.58

−2.4

384

12377

8376

80.002665

0.000154

0.055750

CE2-zr21

262

2316

0.05480

0.0003

0.43956

0.0057

0.0582

0.0007

0.23

−10.1

404

20370

8365

80.000897

0.000052

0.019365

CE2-zr22

541

3441

0.05428

0.0002

0.44533

0.0053

0.0595

0.0007

0.49

−2.7

383

14374

8373

80.001879

0.000108

0.039793

CE2-zr24

419

3797

0.05470

0.0002

0.44715

0.0057

0.0593

0.0007

0.55

−7.4

400

16375

8371

80.001430

0.000083

0.030561

CE2-zr25

456

7878

0.05413

0.0002

0.44395

0.0052

0.0595

0.0007

0.48

−1.1

377

14373

8373

80.001537

0.000088

0.032864

CE2-zr27

497

3185

0.05414

0.0002

0.43491

0.0053

0.0583

0.0007

0.59

−3.2

377

12367

8365

80.001645

0.000094

0.035892

CE2-zr28

542

411150

0.05415

0.0003

0.44505

0.0048

0.0596

0.0006

0.70

−1.2

377

20374

6373

80.001741

0.000100

0.037490

CE2-zr29

496

5280

0.05393

0.0002

0.43612

0.0056

0.0587

0.0007

0.58

−0.2

368

14368

8367

80.001655

0.000095

0.035884

CE2-zr30

422

4009

0.05398

0.0002

0.43776

0.0058

0.0588

0.0007

0.66

−0.5

370

20369

8368

80.001412

0.000081

0.030577

CE2-zr31

361

1484

0.05385

0.0002

0.43230

0.0055

0.0582

0.0007

0.46

.365

16365

8365

80.001191

0.000068

0.026085

CE2-zr34

295

2791

0.05460

0.0002

0.44613

0.0057

0.0593

0.0007

0.28

−6.4

396

16375

8371

80.000981

0.000057

0.021164

CE2-zr35

376

3255

0.05356

0.0002

0.43528

0.0056

0.0590

0.0007

0.67

4.8

353

14367

8369

80.001233

0.000070

0.026849

CE2-zr37

642

3039

0.05405

0.0002

0.44752

0.0055

0.0601

0.0007

0.53

0.7

373

12376

8376

80.002124

0.000122

0.045521

CE2-zr39

728

7700

0.05390

0.0002

0.44983

0.0054

0.0605

0.0007

0.66

3.4

367

12377

8379

80.002355

0.000134

0.050521

CE2-zr40

482

22505

0.05416

0.0002

0.44101

0.0052

0.0591

0.0007

0.65

−2.1

378

14371

8370

80.001496

0.000086

0.032991

CE2-zr43

435

3297

0.05416

0.0002

0.43795

0.0057

0.0587

0.0007

0.31

−2.8

378

14369

8367

80.001372

0.000079

0.030431

CE2-zr44

496

6278

0.05413

0.0002

0.44766

0.0056

0.0600

0.0007

0.62

−0.2

376

16376

8376

80.001587

0.000091

0.034485

CE2-zr46

465

3509

0.05383

0.0002

0.44377

0.0058

0.0598

0.0007

0.39

3364

16373

8374

80.001486

0.000085

0.032378

CE2-zr49

365

2892

0.05494

0.0003

0.44536

0.0061

0.0588

0.0008

0.31

−10.5

410

22374

8368

100.001143

0.000066

0.025383

CE2-zr5

1842

13851

0.05387

0.0002

0.45148

0.0054

0.0608

0.0007

0.59

4.2

366

12378

8380

80.007158

0.000410

0.142732

CE2-zr51

507

6998

0.05452

0.0002

0.45174

0.0059

0.0601

0.0007

0.50

−4.3

392

14378

8376

100.001607

0.000093

0.035024

CE2-zr52

351

1680

0.05462

0.0002

0.45181

0.0057

0.0600

0.0007

0.32

−5.4

397

16379

8376

80.001098

0.000064

0.024036

CE2-zr56

548

8275

0.05394

0.0002

0.44848

0.0054

0.0603

0.0007

0.55

2.5

368

12376

8377

80.001679

0.000096

0.036754


Tab

le2

(contin

ued)

Area

Uppm

206/204

207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/238U*

1SE

Rho

Discordance

207Pb/206Pb

2σ207Pb/235U

2σ206Pb/238U

2σVoltsignal


Sam

ple/grain

%Age

(Ma)

Age

(Ma)

Age

(Ma)

206

207

238

CE2-zr57

711

8682

0.05419

0.0002

0.45233

0.0059

0.0605

0.0008

0.35

.379

14379

8379

100.002225

0.000128

0.048550

CE2-zr7

515

3381

0.05387

0.0002

0.43722

0.0053

0.0589

0.0007

0.38

0.8

366

14368

8369

80.001900

0.000109

0.039475

CE2-zr8

400

3113

0.05432

0.0002

0.44038

0.0051

0.0588

0.0007

0.64

−4.3

384

16371

8368

80.001452

0.000084

0.030414

CE2-zr9

268

2752

0.05381

0.0002

0.43395

0.0054

0.0585

0.0007

0.50

0.9

363

16366

8366

80.000977

0.000056

0.020522

CE3-zr107

638

5136

0.05377

0.0003

0.43932

0.0054

0.0593

0.0006

0.35

2.7

361

22370

8371

60.001926

0.000110

0.044705

CE3-zr12

222

1760

0.05504

0.0004

0.44194

0.0061

0.0583

0.0006

0.04

−12.1

414

34372

8365

60.000697

0.000041

0.016033

CE3-zr123

1199

10727

0.05368

0.0002

0.44298

0.0050

0.0599

0.0006

0.71

4.9

358

16372

6375

60.003635

0.000207

0.083772

CE3-zr129

1780

6848

0.05453

0.0002

0.45091

0.0049

0.0600

0.0006

0.77

−4.6

393

14378

6375

60.005372

0.000311

0.123768

CE3-zr135

1477

9620

0.05391

0.0003

0.44275

0.0054

0.0596

0.0006

0.53

1.5

367

20372

8373

60.004457

0.000255

0.103111

CE3-zr20

1427

7933

0.05414

0.0002

0.44685

0.0046

0.0599

0.0006

0.56

−0.6

377

12375

6375

60.004486

0.000259

0.100578

CE3-zr22

1468

9456

0.05401

0.0002

0.44167

0.0049

0.0593

0.0005

0.42

.372

18371

6371

60.004674

0.000269

0.105769

CE3-zr23

849

6361

0.05488

0.0002

0.44509

0.0045

0.0588

0.0005

0.58

−9.8

407

18374

6369

60.002646

0.000155

0.060505

CE3-zr26

1050

14090

0.05385

0.0003

0.43586

0.0054

0.0587

0.0006

0.49

0.8

365

22367

8368

60.003283

0.000188

0.075179

CE3-zr29

1212

5549

0.05482

0.0002

0.44975

0.0051

0.0595

0.0005

0.55

−8.2

405

18377

8373

60.003855

0.000225

0.087171

CE3-zr31

928

11616

0.05424

0.0002

0.44573

0.0049

0.0596

0.0005

0.48

−2.1

381

16374

6373

60.002941

0.000170

0.066480

CE3-zr33

1008

9168

0.05386

0.0002

0.43466

0.0049

0.0585

0.0005

0.57

0.4

365

18366

6367

60.003146

0.000180

0.072405

CE3-zr34

1602

10294

0.05390

0.0002

0.44589

0.0048

0.0600

0.0006

0.80

2.5

367

14374

6376

60.004995

0.000287

0.112398

CE3-zr4

1136

3973

0.05472

0.0003

0.44268

0.0055

0.0587

0.0006

0.66

−8.5

401

20372

8368

80.003595

0.000210

0.081835

CE3-zr41

898

6630

0.05362

0.0002

0.44093

0.0050

0.0596

0.0006

0.41

5.2

355

18371

6373

60.002794

0.000159

0.063300

CE3-zr42

718

18023

0.05377

0.0002

0.43879

0.0052

0.0592

0.0006

0.70

2.6

362

20369

8371

60.002230

0.000128

0.050907

CE3-zr43

1052

5418

0.05388

0.0002

0.43986

0.0049

0.0592

0.0005

0.53

1.4

366

18370

6371

60.003274

0.000188

0.074782

CE3-zr44

235

2185

0.05385

0.0003

0.43341

0.0051

0.0584

0.0006

0.51

0.3

365

22366

8366

60.000730

0.000042

0.016890

CE3-zr47

1347

14476

0.05372

0.0002

0.43971

0.0049

0.0594

0.0006

0.68

3.5

359

16370

6372

60.004157

0.000238

0.094827

CE3-zr50

980

10379

0.05385

0.0003

0.44344

0.0055

0.0597

0.0006

0.54

2.5

365

22373

8374

60.003080

0.000176

0.069774

CE3-zr51

1071

8840

0.05415

0.0002

0.44479

0.0048

0.0596

0.0005

0.65

−1.1

377

16374

6373

60.003342

0.000193

0.076055

CE3-zr53

905

91273

0.05396

0.0002

0.43870

0.0048

0.0590

0.0005

0.61

.369

16369

6369

60.002796

0.000161

0.064311

CE3-zr54

913

24959

0.05359

0.0003

0.43955

0.0052

0.0595

0.0006

0.69

5.4

354

22370

8373

60.002823

0.000161

0.064528

CE3-zr55

603

7642

0.05421

0.0002

0.43706

0.0048

0.0585

0.0005

0.72

−3.6

380

16368

6366

60.001835

0.000106

0.042752

CE3-zr56

1034

11430

0.05398

0.0003

0.44298

0.0055

0.0595

0.0006

0.82

0.7

370

22372

8373

60.003199

0.000183

0.073157

CE3-zr6

1552

4441

0.05495

0.0002

0.44801

0.0049

0.0591

0.0006

0.69

−10

410

16376

6370

60.004745

0.000278

0.107550

CE3-zr60

1251

23340

0.05399

0.0002

0.44597

0.0049

0.0599

0.0006

0.41

1.2

371

14374

6375

60.003805

0.000218

0.086720

CE3-zr63

700

6957

0.05459

0.0002

0.43934

0.0049

0.0584

0.0005

0.57

−7.7

395

18370

6366

60.002100

0.000122

0.049133

CE3-zr70

1340

6321

0.05507

0.0003

0.44911

0.0056

0.0592

0.0006

0.66

−11

415

22377

8371

60.004106

0.000240

0.094659

CE3-zr71

1409

11143

0.05399

0.0003

0.44726

0.0055

0.0601

0.0006

0.87

1.6

371

22375

8376

80.004365

0.000250

0.099220

CE3-zr72

1146

9603

0.05363

0.0002

0.43977

0.0051

0.0595

0.0006

0.80

4.9

355

18370

8372

60.003519

0.000200

0.080898

CE3-zr73

1201

9544

0.05423

0.0002

0.45340

0.0050

0.0607

0.0006

0.64

−0.3

380

16380

6380

60.003697

0.000213

0.083686

CE3-zr8

1102

8336

0.05396

0.0002

0.43790

0.0049

0.0589

0.0006

0.52

−0.2

369

18369

6369

60.003505

0.000202

0.079669

CE3-zr80

1144

12383

0.05390

0.0003

0.43535

0.0052

0.0586

0.0006

0.53

.367

20367

8367

60.003426

0.000196

0.080146

CE3-zr86

1164

6471

0.05407

0.0002

0.44420

0.0051

0.0596

0.0006

0.56

−0.2

374

16373

8373

60.003506

0.000201

0.080959

CE3-zr97

1004

4616

0.05375

0.0002

0.44395

0.0048

0.0599

0.0006

0.50

4.1

361

14373

6375

60.003041

0.000173

0.070017

CE4-zr100

1328

8040

0.05394

0.0002

0.43729

0.0038

0.0588

0.0004

0.48

−0.1

369

18368

6368

40.004238

0.000242

0.100436

CE4-zr102

1092

43019

0.05343

0.0002

0.43552

0.0035

0.0591

0.0004

0.65

6.9

347

16367

4370

40.003538

0.000200

0.083268

CE4-zr106

674

9258

0.05360

0.0002

0.43215

0.0035

0.0585

0.0004

0.21

3.4

354

20365

4366

40.002166

0.000123

0.051472

CE4-zr109

346

72349

0.05386

0.0003

0.43259

0.0037

0.0583

0.0004

0.53

.365

22365

6365

40.001108

0.000063

0.026446

CE4-zr112

1159

11089

0.05374

0.0002

0.43607

0.0037

0.0589

0.0004

0.53

2.3

360

18367

6369

40.003713

0.000212

0.088006

CE4-zr113

1402

14068

0.05346

0.0002

0.43554

0.0037

0.0591

0.0004

0.72

6.4

348

16367

6370

40.004499

0.000255

0.106239

CE4-zr117

1045

6959

0.05387

0.0002

0.43614

0.0039

0.0587

0.0004

0.61

0.6

366

18368

6368

40.003351

0.000191

0.079650

CE4-zr13

1448

3525

0.05456

0.0002

0.44962

0.0049

0.0598

0.0006

0.76

−5.2

394

16377

6374

60.004353

0.000252

0.101036

CE4-zr16

917

3653

0.05415

0.0003

0.44280

0.0055

0.0593

0.0006

0.57

−1.7

377

22372

8371

60.002728

0.000157

0.063689

CE4-zr20

944

4343

0.05398

0.0002

0.44230

0.0035

0.0594

0.0004

0.65

0.5

370

16372

4372

40.003057

0.000175

0.070925

CE4-zr27

1130

4395

0.05444

0.0002

0.44302

0.0040

0.0590

0.0004

0.77

−5.2

389

20372

6370

40.003610

0.000208

0.084448

CE4-zr31

1302

3852

0.05452

0.0002

0.44641

0.0041

0.0594

0.0004

0.87

−5.5

393

16375

6372

60.004189

0.000242

0.097140

CE4-zr39

1388

4494

0.05402

0.0002

0.43896

0.0039

0.0589

0.0004

0.87

−0.8

372

16370

6369

40.004446

0.000255

0.104082

CE4-zr43

977

11601

0.05374

0.0003

0.43578

0.0039

0.0588

0.0004

0.60

2.4

360

20367

6368

40.003135

0.000178

0.073474


Tab

le2

(contin

ued)

Area

Uppm

206/204

207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/238U*

1SE

Rho

Discordance

207Pb/206Pb

2σ207Pb/235U

2σ206Pb/238U

2σVoltsignal


Sam

ple/grain

%Age

(Ma)

Age

(Ma)

Age

(Ma)

206

207

238

CE4-zr44

993

6768

0.05370

0.0002

0.43693

0.0035

0.0590

0.0004

0.71

3.3

358

16368

4370

40.003198

0.000182

0.074832

CE4-zr49

1145

5324

0.05425

0.0002

0.44124

0.0036

0.0590

0.0004

0.53

−3.3

382

16371

6369

40.003678

0.000211

0.086230

CE4-zr56

1017

4387

0.05395

0.0002

0.43709

0.0035

0.0588

0.0004

0.53

−0.2

369

16368

4368

40.003259

0.000186

0.076663

CE4-zr59

885

5451

0.05385

0.0002

0.44393

0.0039

0.0598

0.0004

0.67

2.6

365

18373

6374

60.002858

0.000163

0.066285

CE4-zr6

1095

2641

0.05454

0.0002

0.44793

0.0050

0.0596

0.0006

0.67

−5.4

394

16376

6373

60.003273

0.000189

0.076176

CE4-zr61

1122

7099

0.05372

0.0002

0.43672

0.0038

0.0590

0.0004

0.86

2.9

359

16368

6369

40.003599

0.000205

0.084532

CE4-zr62

1051

4909

0.05410

0.0002

0.43662

0.0038

0.0585

0.0004

0.53

−2.4

375

18368

6367

40.003344

0.000192

0.079188

CE4-zr63

985

9128

0.05355

0.0002

0.43331

0.0036

0.0587

0.0004

0.64

4.5

352

16366

6368

40.003148

0.000179

0.074162

CE4-zr64

1231

10678

0.05434

0.0003

0.44024

0.0041

0.0588

0.0004

0.59

−4.5

385

22370

6368

40.003945

0.000227

0.092727

CE4-zr67

826

3948

0.05464

0.0003

0.44846

0.0041

0.0595

0.0004

0.20

−6.4

397

22376

6373

60.002678

0.000155

0.062156

CE4-zr68

956

10137

0.05362

0.0002

0.43885

0.0038

0.0594

0.0004

0.69

4.7

355

18369

6372

40.003100

0.000176

0.072312

CE4-zr8

1313

7388

0.05394

0.0003

0.44035

0.0056

0.0592

0.0006

0.83

0.6

369

22370

8371

80.003923

0.000224

0.091471

CE4-zr80

1299

5986

0.05443

0.0002

0.44462

0.0038

0.0593

0.0004

0.84

−4.7

389

18374

6371

40.004210

0.000243

0.098566

CE4-zr84

1183

11119

0.05375

0.0002

0.43719

0.0037

0.0590

0.0004

0.50

2.6

361

16368

6370

40.003797

0.000216

0.089365

CE4-zr96

260

2177

0.05467

0.0003

0.43934

0.0040

0.0583

0.0004

0.29

−8.7

399

22370

6365

40.000829

0.000048

0.019730

CE4-zr99

1464

8304

0.05430

0.0003

0.44913

0.0048

0.0600

0.0005

0.67

−2.1

383

22377

6376

60.004568

0.000263

0.106990

Caveira

CAV2-zr63

991034

0.05680

0.0009

0.45048

0.0080

0.0577

0.0007

0.66

−26.2

484

62378

12362

80.000299

0.000019

0.006776

CAV2-zr57

128

1203

0.05695

0.0007

0.45345

0.0063

0.05792

0.0007

0.43

−26.8

490

52380

8363

80.000390

0.000024

0.008789

CAV2-zr45

103

1243

0.05838

0.0008

0.46818

0.0079

0.05833

0.0007

0.66

−34

544

60390

10365

80.000318

0.000020

0.007077

CAV2-zr25

145

1246

0.06356

0.0012

0.51119

0.0104

0.05848

0.0007

0.41

−51.1

727

78419

14366

80.000456

0.000032

0.009984

CAV2-zr37

651254

0.05864

0.001

0.47111

0.0085

0.05843

0.0007

0.18

−35

554

70392

12366

80.000201

0.000013

0.004446

CAV2-zr5

167

1334

0.05577

0.0006

0.44116

0.0056

0.05748

0.0007

0.45

−19.4

443

46371

8360

80.000525

0.000032

0.011484

CAV2-zr11

528

1434

0.05881

0.0006

0.47282

0.0054

0.05843

0.0007

0.67

−35.8

560

40393

8366

80.001677

0.000107

0.036316

CAV2-zr29

152

1569

0.05619

0.0007

0.45127

0.0067

0.05838

0.0007

0.35

−21.3

460

56378

10366

80.000476

0.000029

0.010465

CAV2-zr9

116

1664

0.05649

0.0008

0.45190

0.0081

0.05814

0.0007

0.65

−23.5

472

64379

12364

80.000366

0.000022

0.007974

CAV2-zr32

285

1770

0.05587

0.0005

0.44603

0.0052

0.05804

0.0007

0.66

−19.4

447

42374

8364

80.000886

0.000054

0.019621

CAV2-zr20

221

2129

0.06018

0.0009

0.48862

0.0089

0.05902

0.0007

0.80

−40.7

610

68404

12370

80.000704

0.000046

0.015225

CAV2-zr43

732190

0.05864

0.001

0.47123

0.0092

0.05845

0.0007

0.52

−35

554

70392

12366

80.000226

0.000014

0.005012

CAV2-zr16

194

2240

0.05484

0.0006

0.43365

0.0060

0.05748

0.0007

0.71

−11.7

406

48366

8360

80.000601

0.000036

0.013309

CAV2-zr26

191

2247

0.05537

0.0006

0.44057

0.0057

0.05785

0.0007

0.36

−15.8

427

48371

8363

80.000593

0.000036

0.013138

CAV2-zr17

180

2752

0.06098

0.0009

0.48704

0.0078

0.05806

0.0007

0.27

−44.4

639

60403

10364

80.000563

0.000037

0.012368

CAV2-zr13

428

6065

0.05616

0.0005

0.44375

0.0052

0.05742

0.0007

0.68

−22.3

459

42373

8360

80.001333

0.000081

0.029423

Az.

Barros

AZI4zr1a

408

5009

0.05364

0.0002

0.42257

0.0053

0.0574

0.0007

0.64

0.7

356

18358

8360

80.001728

0.000097

0.039206

AZI4zr2a

156

1501

0.05367

0.0003

0.42865

0.0055

0.0582

0.0007

0.36

1.7

357

24362

8364

80.000670

0.000038

0.015022

AZI4zr3a

512

3914

0.05401

0.0002

0.43002

0.0053

0.0580

0.0007

0.65

−2.6

371

16363

8363

80.002182

0.000123

0.049116

Alju

strel

FEV1-zr12

289

1611

0.05380

0.0002

0.43139

0.0034

0.0582

0.0004

0.70

0.5

363

16364

4364

60.001300

0.000075

0.030630

FEV1-zr18

193

20442

0.17860

0.0005

12.41971

0.0978

0.5043

0.0037

0.93

−0.3

2640

102637

142632

320.007420

0.001420

0.020199

FEV1-zr23

235

2744

0.05335

0.0003

0.43511

0.0050

0.0592

0.0005

0.41

8.1

344

24367

8371

60.001139

0.000065

0.026181

FEV1-zr24

108

1049

0.05366

0.0004

0.43129

0.0053

0.0583

0.0005

0.50

2.5

357

30364

8365

60.000516

0.000030

0.012051

FEV1-zr34b

154

2058

0.05345

0.0004

0.42740

0.0036

0.0580

0.0007

0.74

4.5

348

34361

6363

80.000764

0.000044

0.018166

FEV1-zr5

202

2064

0.05360

0.0002

0.43068

0.0032

0.0583

0.0004

0.25

3.1

354

18364

4365

40.000935

0.000054

0.021817

FEV1-zr6

150

1496

0.05366

0.0002

0.43280

0.0035

0.0585

0.0004

0.65

2.8

357

20365

4367

40.000688

0.000040

0.016102

FEV1-zr8

962896

0.05993

0.0003

0.81896

0.0067

0.0991

0.0007

0.35

1.4

601

20607

8609

80.000751

0.000048

0.010332

FEV2-zr10

208

1716

0.05374

0.0004

0.41619

0.0035

0.0562

0.0007

0.56

−2.3

360

32353

4352

80.001008

0.000057

0.023903

FEV2-zr11

431

4776

0.05403

0.0004

0.42041

0.0032

0.0564

0.0007

0.37

−5.1

372

30356

4354

80.002103

0.000119

0.049587

FEV2-zr13

207

1364

0.05409

0.0004

0.42233

0.0035

0.0566

0.0007

0.15

−5.5

375

28358

4355

80.001025

0.000058

0.023933


Tab

le2

(contin

ued)

Area

Uppm

206/204

207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/238U*

1SE

Rho

Discordance

207Pb/206Pb

2σ207Pb/235U

2σ206Pb/238U

2σVoltsignal


Sam

ple/grain

%Age

(Ma)

Age

(Ma)

Age

(Ma)

206

207

238

FEV2-zr15

238

1913

0.05349

0.0004

0.41614

0.0036

0.0564

0.0007

0.63

1.2

350

30353

6354

80.001168

0.000066

0.027432

FEV2-zr17

128

1915

0.05354

0.0004

0.42723

0.0038

0.0579

0.0007

0.53

3.2

352

32361

6363

80.000648

0.000036

0.014802

FEV2-zr18

166

5174

0.05378

0.0004

0.41541

0.0037

0.0560

0.0007

0.47

−2.9

362

30353

6351

80.000813

0.000046

0.019166

FEV2-zr23

676

5062

0.05377

0.0004

0.42755

0.0037

0.0577

0.0007

0.41

.361

30361

6361

80.003414

0.000192

0.077870

FEV2-zr26

176

3034

0.05408

0.0004

0.42835

0.0039

0.0575

0.0007

0.70

−3.9

374

32362

6360

80.000883

0.000050

0.020233

FEV2-zr27

588

3695

0.05430

0.0004

0.42954

0.0034

0.0574

0.0007

0.66

−6.4

383

30363

4360

80.002933

0.000166

0.067413

FEV2-zr31

119

1848

0.05364

0.0004

0.42842

0.0039

0.0579

0.0007

0.44

2.1

356

32362

6363

80.000600

0.000034

0.013642

FEV2-zr32

123

4304

0.05451

0.0005

0.42174

0.0038

0.0561

0.0007

0.17

−10.6

392

36357

6352

80.000601

0.000034

0.014113

FEV2-zr8

167

1735

0.05406

0.0004

0.41465

0.0036

0.0556

0.0007

0.65

−6.7

374

30352

6349

80.000809

0.000046

0.019336

FEV2-zr9

184

2395

0.05429

0.0004

0.41928

0.0035

0.0560

0.0007

0.44

−8.5

383

30356

4351

80.000892

0.000051

0.021184

SJ1-zr12

801051

0.06067

0.0004

0.81045

0.0091

0.0969

0.0007

0.47

−5.2

627

28603

10596

80.000418

0.000027

0.006082

SJ1-zr15

254

1566

0.05371

0.0002

0.42009

0.0034

0.0567

0.0004

0.11

−0.9

359

18356

4356

40.000793

0.000045

0.019607

SJ1-zr17

113

2439

0.05352

0.0003

0.41409

0.0043

0.0561

0.0004

0.29

0.3

351

28352

6352

60.000352

0.000020

0.008769

SJ1-zr19

220

2318

0.05543

0.0005

0.43113

0.0055

0.0565

0.0008

0.17

−18.1

430

42364

8354

100.000959

0.000057

0.024156

SJ1-zr2

370

1064

0.05340

0.0003

0.41908

0.0038

0.0569

0.0004

0.39

3.3

346

20355

6357

40.001147

0.000065

0.028138

SJ1-zr22

214

1834

0.05360

0.0008

0.42888

0.0055

0.0581

0.0007

0.65

2.7

354

70362

8364

80.000964

0.000055

0.023862

SJ1-zr25

328

8784

0.05371

0.0009

0.42410

0.0055

0.0574

0.0007

0.76

.359

74359

8360

80.001470

0.000084

0.037017

SJ1-zr27

677

10295

0.05366

0.0010

0.41981

0.0058

0.0569

0.0008

0.83

−0.3

357

82356

8356

100.003031

0.000173

0.076894

SJ1-zr28

672866

0.05385

0.0009

0.41534

0.0056

0.0561

0.0007

0.22

−3.9

365

78353

8352

80.000293

0.000017

0.007535

SJ1-zr29

234

2723

0.05465

0.0010

0.42184

0.0064

0.0561

0.0007

0.53

−12.1

398

76357

10352

100.001022

0.000060

0.026165

SJ1-zr30

128

1652

0.05372

0.0008

0.42420

0.0054

0.0574

0.0007

0.23

−0.1

359

70359

8360

80.000571

0.000033

0.014345

SJ1-zr33

101

1549

0.05377

0.0009

0.42630

0.0055

0.0576

0.0008

0.49

−0.2

361

72361

8361

100.000455

0.000026

0.011398

SJ1-zr39

224

6408

0.06140

0.0009

0.81602

0.0109

0.0965

0.0013

0.18

−9.6

653

62606

12594

160.001679

0.000110

0.024937

SJ1-zr41

112

3437

0.06096

0.0010

0.86823

0.0122

0.1034

0.0015

0.64

−0.7

638

64635

14634

180.000897

0.000058

0.012455

SJ1-zr42

326

7256

0.05353

0.0009

0.41313

0.0053

0.0561

0.0007

0.77

−0.1

352

76351

8352

80.001427

0.000082

0.036779

SJ1-zr43

182

2579

0.05341

0.0008

0.42304

0.0056

0.0576

0.0007

0.79

4346

68358

8361

100.000811

0.000046

0.020357

SJ1-zr44

107

1271

0.05325

0.0009

0.41976

0.0061

0.0573

0.0008

0.70

5.7

339

74356

8359

100.000481

0.000027

0.012130

SJ1-zr45

601008

0.05376

0.0009

0.43135

0.0060

0.0584

0.0008

0.28

1.1

361

76364

8366

100.000272

0.000016

0.006727

SJ1-zr46

502935

0.05366

0.0011

0.42266

0.0064

0.0573

0.0007

0.43

0.3

357

86358

10359

100.000225

0.000013

0.005675

SJ1-zr47

273

1583

0.05369

0.0003

0.42295

0.0039

0.0571

0.0004

0.50

.358

22358

6358

40.000861

0.000049

0.021021

SJ1-zr5

371

5221

0.05329

0.0002

0.41746

0.0037

0.0568

0.0004

0.71

4.5

341

18354

6356

40.001154

0.000065

0.028374

SJ1-zr6

178

942

0.05898

0.0003

0.71443

0.0076

0.0879

0.0007

0.86

−4.4

567

22547

8543

80.000858

0.000054

0.013640

SJ1-zr7

447

1865

0.05342

0.0002

0.41487

0.0036

0.0563

0.0004

0.48

2346

18352

6353

40.001380

0.000078

0.034239

SJ2-zr13

199

3185

0.05408

0.0003

0.42163

0.0037

0.0566

0.0004

0.77

−5.4

374

20357

6355

40.000955

0.000056

0.022876

SJ2-zr14

114

1381

0.05367

0.0002

0.42620

0.0034

0.0576

0.0004

0.52

1.1

357

20360

4361

40.000556

0.000032

0.013001

SJ2-zr20

312

2557

0.05434

0.0002

0.45909

0.0048

0.0613

0.0006

0.92

−0.5

385

18384

6383

80.001586

0.000094

0.035022

SJ2-zr21

314

5930

0.05340

0.0002

0.43160

0.0035

0.0586

0.0004

0.69

6.4

346

20364

6367

40.001555

0.000090

0.036031

SJ2-zr23

285

1995

0.05418

0.0003

0.42174

0.0038

0.0565

0.0003

0.83

−6.6

378

22357

6354

40.001342

0.000079

0.032545

SJ2-zr24

389

3550

0.05403

0.0002

0.44221

0.0037

0.0594

0.0004

0.86

−0.2

372

14372

6372

60.001893

0.000111

0.043345

SJ2-zr26

148

1088

0.05498

0.0003

0.45194

0.0036

0.0596

0.0005

0.34

−9.5

411

22379

6373

60.000717

0.000043

0.016239

SJ2-zr27

317

3899

0.05364

0.0002

0.44025

0.0033

0.0595

0.0004

0.53

4.8

356

16370

4373

40.001538

0.000089

0.034989

SJ2-zr3

109

1885

0.05374

0.0003

0.42339

0.0035

0.0572

0.0004

0.47

−0.6

360

22358

4358

60.000549

0.000032

0.012769

Albernoa

CO5zr1a

190

3988

0.05357

0.0005

0.42887

0.0090

0.0582

0.0010

0.34

3.1

353

42362

12365

120.000781

0.000044

0.017457

CO5zr2a

331

3145

0.05421

0.0002

0.42497

0.0055

0.0571

0.0007

0.38

−6.3

380

20360

8358

80.001397

0.000079

0.032030

CO5zr4a

179

1066

0.05414

0.0003

0.40901

0.0057

0.0550

0.0007

0.53

−8.9

377

26348

8345

80.000728

0.000041

0.017352

CO5zr8a

403

25929

0.05482

0.0002

0.42732

0.0061

0.0567

0.0007

0.59

−12.8

405

20361

8356

80.001646

0.000094

0.038107

CO5zr9a

753

23412

0.05414

0.0002

0.41837

0.0048

0.0563

0.0006

0.62

−6.9

377

16355

6353

80.003071

0.000174

0.072552

CO5zr10a

330

2283

0.05453

0.0003

0.42148

0.0053

0.0563

0.0006

0.33

−10.8

393

20357

8353

80.001353

0.000077

0.031877

IP4-zr1a

748

7808

0.05326

0.0004

0.41837

0.0102

0.0568

0.0010

0.83

5.2

340

36355

14356

120.003004

0.000162

0.082052

IP4-zr2a

249

5090

0.05352

0.0004

0.42794

0.0103

0.0579

0.0010

0.66

3.6

351

34362

14363

120.001009

0.000055

0.027157

IP4zr5a

153

1513

0.05293

0.0005

0.42299

0.0105

0.0578

0.0010

0.66

11.7

326

44358

16362

120.000636

0.000034

0.017412

IP4Z

r8a

200

4953

0.05357

0.0005

0.41809

0.0029

0.0564

0.0007

0.54

0.5

353

36355

4354

80.000803

0.000044

0.021511

IP4Z

r12a

754

10016

0.05405

0.0004

0.42227

0.0024

0.0565

0.0006

0.30

−5.0

373

34358

4354

80.003037

0.000168

0.081186

IP4Z

r13a

154

8182

0.05317

0.0005

0.41958

0.0033

0.0570

0.0007

0.48

6.9

336

42356

4358

80.000624

0.000034

0.016569


Tab

le2

(contin

ued)

Area

Uppm

206/204

207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/238U*

1SE

Rho

Discordance

207Pb/206Pb

2σ207Pb/235U

2σ206Pb/238U

2σVoltsignal


Sam

ple/grain

%Age

(Ma)

Age

(Ma)

Age

(Ma)

206

207

238

IP4Z

r14a

184

2046

0.05400

0.0005

0.42525

0.0032

0.0569

0.0007

0.68

−3.6

371

36360

4357

80.000743

0.000041

0.019791

Serra

Branca

SB55zr1a

705

7788

0.05390

0.0005

0.43581

0.0021

0.0586

0.0007

0.39

0.1

367

42367

2367

80.002986

0.000165

0.081022

SB55zr2a

139

2472

0.05297

0.0006

0.43125

0.0038

0.0590

0.0007

0.50

13.3

328

52364

6369

80.000591

0.000032

0.015977

SB55zr3a

331

5968

0.05344

0.0005

0.43248

0.0028

0.0586

0.0007

0.79

6.0

347

44365

4367

80.001429

0.000079

0.038007

SB8-89,7zr1a

220

1594

0.05379

0.0003

0.41955

0.0055

0.0568

0.0007

0.70

−2.2

362

22356

8356

80.000900

0.000051

0.021318

SB8-89,7zr4a

313

6599

0.05427

0.0003

0.42398

0.0052

0.0569

0.0006

0.70

−7.3

382

22359

8357

80.001289

0.000073

0.030283

SB54zr1a

236

38323

0.18216

0.0026

13.29061

0.1346

0.5223

0.0097

0.97

3.0

2673

442701

202709

820.008127

0.001497

0.025177

SB54zr1b

107

5410

0.11917

0.0015

1.90884

0.0147

0.1167

0.0012

0.74

−67

1944

441084

10711

140.000873

0.000105

0.011960

Chança

CH601-zr1

115

1093

0.05337

0.0004

0.42034

0.0036

0.0571

0.0007

0.10

4.1

345

34356

6358

80.000559

0.000032

0.013458

CH601-zr10

183

1423

0.05343

0.0004

0.42052

0.0037

0.0571

0.0007

0.39

3.2

347

34356

6358

80.000903

0.000052

0.021579

CH601-zr13

197

1852

0.05352

0.0004

0.41304

0.0036

0.0560

0.0007

0.45

.351

32351

6351

80.000949

0.000054

0.023031

CH601-zr19

971111

0.05312

0.0004

0.41397

0.0039

0.0565

0.0007

0.46

6.4

334

34352

6354

80.000473

0.000027

0.011363

CH601-zr2

151

1146

0.05300

0.0004

0.41225

0.0034

0.0564

0.0007

0.11

7.8

329

32350

4354

80.000720

0.000041

0.017533

CH601-zr20

103

1385

0.05341

0.0004

0.42326

0.0038

0.0575

0.0007

0.55

4.2

346

34358

6360

80.000503

0.000029

0.011908

CH601-zr22

125

1308

0.05308

0.0004

0.42336

0.0037

0.0579

0.0007

0.36

9.4

332

32358

6363

80.000624

0.000035

0.014612

CH601-zr23

150

2308

0.05354

0.0004

0.42215

0.0038

0.0572

0.0007

0.24

2352

32358

6358

80.000744

0.000042

0.017567

CH601-zr24

156

1317

0.05339

0.0005

0.42712

0.0043

0.0580

0.0007

0.36

5.4

346

40361

6364

80.000778

0.000044

0.018135

CH601-zr26

150

1847

0.05353

0.0004

0.41866

0.0038

0.0567

0.0007

0.43

1.3

351

34355

6356

80.000741

0.000042

0.017614

CH601-zr27

108

1078

0.05320

0.0005

0.41797

0.0041

0.0570

0.0007

0.57

6337

38355

6357

80.000532

0.000030

0.012626

CH601-zr28

921557

0.05353

0.0004

0.41169

0.0035

0.0558

0.0007

0.69

−0.4

351

32350

6350

80.000442

0.000025

0.010717

CH601-zr29

334

2342

0.05481

0.0003

0.41950

0.0053

0.0555

0.0009

0.69

−14.3

405

24356

8348

120.001561

0.000091

0.037480

CH601-zr30

135

2823

0.05366

0.0004

0.41000

0.0035

0.0554

0.0006

0.54

−2.6

357

32349

6348

80.000638

0.000036

0.015584

CH601-zr31

142

2128

0.05361

0.0004

0.41892

0.0037

0.0567

0.0007

0.42

0.2

355

30355

6355

80.000699

0.000040

0.016561

CH601-zr32

162

1763

0.05350

0.0004

0.41421

0.0036

0.0561

0.0007

0.50

0.6

350

32352

6352

80.000783

0.000044

0.018847

CH601-zr38

178

1746

0.05364

0.0004

0.41570

0.0036

0.0562

0.0007

0.60

−1356

30353

6352

80.000870

0.000050

0.020815

CH601-zr39

333

9913

0.05375

0.0004

0.41197

0.0034

0.0556

0.0007

0.66

−3.3

360

28350

4349

80.001594

0.000091

0.038595

CH601-zr41

157

2041

0.05382

0.0004

0.41565

0.0036

0.0560

0.0007

0.51

−3.5

364

34353

6351

80.000758

0.000043

0.018218

CH601-zr42

219

4284

0.05379

0.0004

0.41459

0.0036

0.0559

0.0007

0.69

−3.3

362

30352

6351

80.001054

0.000060

0.025351

CH601-zr50

151

1498

0.05387

0.0004

0.41913

0.0039

0.0564

0.0007

0.21

−3.4

366

34355

6354

80.000740

0.000042

0.017530

CH601-zr51

166

2772

0.05412

0.0004

0.42175

0.0037

0.0565

0.0007

0.49

−5.9

376

32357

6354

80.000800

0.000046

0.019025

CH601-zr52

161

3259

0.05395

0.0004

0.41062

0.0036

0.0552

0.0007

0.23

−6.2

369

32349

6346

80.000774

0.000044

0.018705

CH601-zr54

104

1721

0.05448

0.0004

0.41522

0.0039

0.0553

0.0006

0.57

−11.6

391

32353

6347

80.000484

0.000028

0.011786

CH602-zr2

241

1659

0.05257

0.0035

0.40062

0.0122

0.0557

0.0008

0.49

12.1

310

302

342

18349

100.000779

0.000044

0.017311

CH602-zr4

144

1570

0.05381

0.0037

0.40202

0.0128

0.0546

0.0008

0.65

−6.5

363

302

343

18343

100.000459

0.000026

0.010346

CH602-zr7

503

1921

0.05404

0.0037

0.41514

0.0137

0.0563

0.0008

0.73

−6.3

373

294

353

20353

100.001671

0.000097

0.036179

CH602-zr9

721057

0.05584

0.0040

0.42752

0.0153

0.0562

0.0009

0.57

−22.5

446

328

361

22352

100.000239

0.000014

0.005156

Lousal

LR23zr1a

637

108469

0.13224

0.0008

6.74812

0.1848

0.3701

0.0085

0.93

−5.4

2128

202079

482030

800.017559

0.002410

0.059075

LR23zr3a

392855

0.10996

0.0007

4.88560

0.1119

0.3219

0.0069

0.70

0.1

1799

201800

381799

660.000930

0.000106

0.003614

LR23zr4a

105

690

0.05956

0.0003

0.77950

0.0118

0.0952

0.0013

0.47

−0.6

588

22585

14586

140.000743

0.000046

0.009939

LR23zr5a

445

7077

0.06057

0.0002

0.85274

0.0123

0.1023

0.0014

0.75

0.4

624

14626

14628

160.003400

0.000215

0.042249

LR23zr6a

156

14600

0.14762

0.0008

8.36275

0.2369

0.4114

0.0092

0.93

−5.1

2319

182271

522221

840.004827

0.000740

0.014693

LR23zr7a

596

3699

0.06151

0.0002

0.85435

0.0117

0.1010

0.0013

0.81

−6.1

657

12627

12620

160.004482

0.000288

0.056881

LR23zr9a

197

6828

0.16377

0.0008

10.40116

0.3174

0.4618

0.0104

0.94

−2.5

2495

162471

562447

920.006907

0.001176

0.018830

LR23zr10a

743459

0.13221

0.0006

6.65939

0.1463

0.3655

0.0070

0.75

−6.6

2127

162067

382008

660.002046

0.000282

0.007090


with sufficient precision to be used in the isobaric overlapcorrection procedure at mass 176 (e.g. Woodhead et al.2004). The isobaric interferences on 176Hf by 176Lu and176Yb were therefore corrected by an empirical procedure

similar to that of Griffin et al. (2000), using the observedmass discrimination for Hf as a proxy for those of Lu andYb. The value of the 176Yb/172Yb ratio to be used in thecorrection procedure was determined from multiple laser

390

3600.057

0.059

0.061

0.063

0.42 0.43 0.44 0.45 0.46 0.47207Pb/235U

206 P

b/23

8 U

Cercal (CE1) Concordia Age=374.3±1.6 Ma (2 σ , , decay-const. errs ignored) MSWD (of concordance)=0.21,

Probability (of concordance)=0.65

358

382

386

0.057

0.058

0.059

0.060

0.061

0.062

0.42 0.43 0.44 0.45 0.46207Pb/235U

206 P

b/23

8 U

Cercal (CE4) Concordia Age=369.50±0.85 Ma

(2σ,decay-const. errs ignored)MSWD (of concordance)=0.086,Probability(of concordance)=0.77

380 370 360 350

0.054

0.058

0.062

0.066

16.2 16.6 17.0 17.4 17.8238U/206Pb

207 P

b/20

6 Pb

380

370

3400.055

0.057

0.059

0.061

0.40 0.41 0.42 0.43 0.44 0.45207Pb/235U

206 P

b/23

8 U

Aljustrel (SJ1)Concordia Age=356.5±1.3 Ma(2σ, decay-const. errs ignored)MSWD (of concordance)=0.67,Prob. (of concordance)=0.41

390

350

0.057

0.059

0.061

0.063

0.41 0.43 0.45207Pb/235U

206 P

b/23

8 U

Cercal (CE2) Conc. Age=371.1±1.2 Ma (2 σ , decay-const. errs ignored) MSWD (of concordance)=0.89,


390

360

0.058

0.060

0.062

0.42 0.43 0.44 0.45 0.46

207Pb/235U

206 P

b/23

8 U

Cercal (CE3) Concordia Age=371.6±1.0 Ma(2σ,decay-const. errs ignored)MSWD (of concordance)=0.70,


376

372

368

364

360

356

352

348

0.055

0.056

0.057

0.058

0.059

0.060

0.41 0.42 0.43 0.44207Pb/235U

206 P

b/23

8 U

Azinheira dos Barros (AZI4)Concordia Age=361.8±4.0 Ma(2σ,decay-const. errs ignored)MSWD (of concordance)=0.37,


344

348

352

356

360

364

0.054

0.055

0.056

0.057

0.058

0.059

0.060

0.41 0.42 0.43207Pb/235U

206 P

b/23

8 U

Aljustrel (FEV2)Concordia Age=354.6 ±1.7 Ma(2σ, decay-const. errs ignored)MSWD (of concordance)=2.3,


Caveira (CAV2)

a b

c d

e f

g h

Fig. 3 Concordia diagrams ofCercal, Caveira, Azinheira deBarros and Aljustrel samples


ablation analyses of grains of the Temora-2 reference zirconwhich show a range of 176Yb/177Hf ratios of ca. 0.01 to 0.1.This procedure was chosen in order to avoid the matrix-dependent mass discrimination problems encountered when

using data from aqueous Yb-spiked Hf standard solutions tocorrect laser ablation analyses (e.g. Iizuka and Hirata 2005).The resulting 176Yb/172Yb=0.58707 is within the range ofpublished isotope ratios for natural Yb (Chu et al. 2002;

366

362

358

354

3500.056

0.057

0.058

0.414 0.418 0.422 0.426 0.430 0.434207Pb/235U

206 P

b/23

8 U

Aljustrel (SJ2)Concordia Age=356.6±2.1 Ma(2σ,decay-const. errs ignored)MSWD (of concordance)=7.4,


380

370

360

350

340

0.055

0.057

0.059

0.40 0.42 0.44207Pb/235U

206 P

b/23

8 U

Albernoa (IP4) Conc. Age=357.2±2.0 Ma(2 σ , decay-const. errs ignored)

MSWD (of concordance)=0.077,Probability(of concordance)=0.78

360

364

368

372

0.058

0.059

0.060

0.061

0.062

0.424 0.428 0.432 0.436 0.440207Pb/235U

206 P

b/23

8 U

Serra Branca (SB55)Concordia Age=365.8±2.1 Ma(2σ,decay-const. errs ignored)MSWD (of concordance)=1.8,


360

350

340

330

0.054

0.056

0.058

0.37 0.39 0.41 0.43 0.45 0.47207Pb/235U

206 P

b/23

8 U

Chança (CH602) Conc. Age=349.0±4.9 Ma (2 σ , decay-const. errs ignored)

MSWD (of concordance)=0.0088,Probability (of concordance)=0.93

378

374

370

366

362

358

354

3500.0565

0.0575

0.0585

0.0595

0.0605

0.42 0.43 0.44 0.45207Pb/235U

206 P

b/23

8 U

Aljustrel (FEV1) Concordia Age=364.0 ±1.7 Ma(2σ,decay-const. errs ignored) MSWD (of concordance)=2.1,


380

360

3400.054

0.058

0.062

0.39 0.41 0.43 0.45 0.47207Pb/235U

206 P

b/23

8 U

Albernoa (CO5)Concordia Age = 355.4 ±2.9 Ma(2s, decay-const. errs ignored)MSWD (of concordance) = 2.5,

Probability (of concordance) = 0.11

366

362

358

35

350

3460.055

0.056

0.057

0.058

0.41 0.42 0.43207Pb/235U

206 P

b/23

8 U

Serra Branca (SB8-89,7)Concordia Age=356.9±5.0 Ma(2σ,decay-const. errs ignored)MSWD (of concordance)=0.22,

Probability(of concordance)=0.64

372

368

360

3400.054

0.056

0.058

0.40 0.41 0.42 0.43207Pb/235U

206 P

b/23

8 U

Chança (CH601) Conc. Age=353.9±1.1 Ma (2σ ,decay-const. errs ignored)MSWD (of concordance)=0.058,


0.44

a b

c d

e f

g h

Fig. 4 Concordia diagrams ofAljustrel (continuation),Albernoa, Serra Branca andChanca samples


Segal et al. 2003). Once established, this correctionprocedure shows good long-term stability, as seen from theresults for reference zircons run as unknowns (Appendix,Table 5). Most significantly, there is no correlation betweencorrected 176Hf/177Hf and 176Yb/177Hf, suggesting that nosystematic bias is caused by under- or overcorrection forinterferences at 176Yb/177Hf≤0.1 (Appendix, Fig. 10).

Avalue for the decay constant of 176Lu of 1.867×10−11 a−1

has been used in all calculations (Söderlund et al. 2004;Scherer et al. 2001, 2007). For the calculation of ɛHf valueswe use present-day chondritic 176Hf/177Hf=0.282802 and176Lu/177Hf=0.0337 (Bouvier et al. 2007). We have adoptedthe depleted mantle model of Griffin et al. (2000) modifiedto the λ176Lu used, which produces a value of 176Hf/177Hf(0.28325, ɛHf=+16) similar to that of average MORB over4.56 Ga, from chondritic initial hafnium at 176Lu/177HfDM=0.0384. This mantle evolution curve is indistinguishablefrom the fLu/Hf=0.16 (i.e. 176Lu/177Hf=0.038) curve ofVervoort & Blichert-Toft (1999).

Standards/reference zircons 91500, Temora-2, Mud Tankand GJ-1 were run as unknowns at frequent intervals. Thedata obtained over a 2-year period indicates excellentaccuracy and an external reproducibility of ±0.000050 (2SD) on the low-REE Mud Tank zircon, and somewhathigher (±0.000065) on the Temora-2 zircon, which hashigher and more variable Yb/Hf (Appendix, Table 5). In thisstudy, a value of ±0.000065 is used as a conservativeestimate of the external reproducibility of the method. Forstandard zircon 91500, we have observed an isotopicheterogeneity similar to that reported by Griffin et al.(2006), which accounts for the worse precision of thatreference sample.

Geochronology

The U–Pb analytical results, for zircon grains from samplesrepresentative of each of the volcanic rock types and of thePQ Formation sample, are compiled in Table 2. U–Pb ageswere calculated using ISOPLOT version 3 (Ludwig 2003),with errors reported at 95% (±2σ) confidence level. Manyzircons in these samples have elevated concentrations ofcommon lead which could not be adequately corrected fromthe observed 206/204 ratios, and which do not definediscordia lines anchored at common lead in a Tera–Wasserburg diagram. Such analyses have been discarded.

The four samples from Cercal, despite having beencollected throughout a rather wide area, provided similarages. Sample CE1 provided 16 concordant grains yielding andage of 374±2Ma (Fig. 3a). Sample CE2 yielded 35 concordantzircon grains, resulting in an age of 371±1 Ma (Fig. 3b).Sample CE3 yielded 36 concordant zircon grains that providean age of 372±1 Ma (Fig. 3c). Sample CE4 was dated at 370±1 Ma, based on 30 concordant zircon grains (Fig. 3d).

In Caveira, only one sample was collected (CAV2), whichyielded zircon grains with substantial amounts of commonlead. On a Tera–Wasserburg diagram the grains define a linewith an unprecise upper intercept (representing commonlead) and a lower intercept at 361±4 Ma, considered the bestestimate for the emplacement of this rock (Fig. 3e).

Three zircons from sample AZI4, from Azinheira deBarros, are concordant at 362±4 Ma, dating the emplace-ment of this rock type (Fig. 3f).

Three of the samples collected in Aljustrel have statisti-cally identical ages; the fine-grained quartz-feldspar-phyricporphyry (FEV2) was dated at 355±2 Ma, based on eightconcordant zircon grains (Fig. 3g), while the megacrystporphyry samples were dated at 356±1 and 357±2 Ma,

2600

2200

1800

1400

1000

0.0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10 12 14

207Pb/235U

206 P

b/23

8 Udata-point error ellipses are 2σ

670

650

630

610

590

570

550

5300.086

0.090

0.094

0.098

0.102

0.106

0.66 0.70 0.74 0.78 0.82 0.86 0.90 0.94

SB54

CE1

FEV1

FEV1

SJ1

SJ1

Fig. 5 Compilation of pre-Variscan inherited zircon grains identifiedduring this study

2600

2200

1800

1400

1000

600

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12 14207Pb/ 235U

206 P

b/23

8 U

data-point error ellipses are 2σ

570

590

610

630

650

0.094

0.098

0.102

0.106

0.72 0.76 0.80 0.84 0.88 0.92

Fig. 6 Concordia diagram for detrital zircon grains from sample LR23 (PQ Formation from Lousal)


based on 19 and four concordant zircon grains, for SJ1 andSJ2, respectively (Figs. 3h and 4a). The coarse-grainedporphyry (FEV1) is significantly older, being dated at 364±2 Ma, based on seven concordant zircon grains (Fig. 4b).

Aljustrel is particular in the sense that two of its youngersamples contain inherited, but still Variscan, zircon grains.In sample FEV2, in addition to the zircon grains mentionedabove that provide an age for the emplacement of themagma, five zircons grains were identified which define a

concordia age of 362±2 Ma. In sample SJ2, two earlierVariscan zircon fractions were identified, one at 384±7 Ma(one grain) and another at 373±3 Ma (three grains).

The best estimate of the crystallization age of samplesCO5 and IP4, both quartz-feldspar-phyric porphyries fromAlbernoa, is provided by two concordia ages of 355±3 and356±2 Ma, based on six and seven concordant analyses,respectively (Fig. 4c and d). A weighted mean of 356±2 Ma for the emplacement of this rock was calculated.

Table 3 Lu-Hf zircon data

AreaSample/grain

U–Pbage(Ma)

176Hf/177Hf 2σ(int. prec.)

176Yb/177Hf 2σ 176Lu/177Hf 2σ 176Hf/177Hf(initial)

Epsilon(initial)

Protolithage (Ga)

CercalCE4-zr116 370 0.282765 0.000022 0.109 0.001 0.00154 0.00002 0.282754 6.6 0.89Azinheira de BarrosAZI4zr2b 362 0.282565 0.000040 0.067 0.004 0.00158 0.00012 0.282555 −0.7 1.34AljustrelFEV1-zr1b 364 0.282519 0.000028 0.068 0.005 0.00103 0.00007 0.282512 −2.1 1.44FEV1-zr8b 355 0.282506 0.000024 0.028 0.004 0.00045 0.00008 0.282503 −2.7 1.46FEV1-zr18b 2639inh 0.280986 0.000022 0.037 0.001 0.00059 0.00002 0.280956 −5.1 3.41FEV1-zr19b 364 0.282553 0.000030 0.116 0.008 0.00170 0.00020 0.282541 −1.1 1.37FEV1-zr34c 364 0.282538 0.000040 0.049 0.008 0.00062 0.00010 0.282534 −1.4 1.39FEV2-zr14b 355 0.282796 0.000026 0.092 0.010 0.00151 0.00030 0.282786 7.4 0.83FEV2-zr31b 362 0.282674 0.000022 0.098 0.007 0.00158 0.00011 0.282663 3.2 1.1FEV2-zr32b 355 0.282780 0.000034 0.087 0.007 0.00133 0.00015 0.282771 6.8 0.86SJ1-zr3b 356 0.282649 0.000026 0.107 0.006 0.00146 0.00005 0.282639 2.2 1.16SJ1-zr7b 356 0.282394 0.000036 0.085 0.013 0.00143 0.00026 0.282384 −6.8 1.73SJ1-zr15b 356 0.282132 0.000078 0.031 0.001 0.00043 0.00003 0.282129 −15.9 2.29SJ1-zr41b 356 0.282541 0.000030 0.092 0.005 0.00137 0.00013 0.282532 −1.6 1.4SJ1-zr42b 356 0.282510 0.000024 0.027 0.001 0.00042 0.00006 0.282507 −2.5 1.45SJ1-zr44b 356 0.282582 0.000030 0.084 0.014 0.00117 0.00020 0.282574 −0.1 1.3SJ2-zr3b 357 0.282549 0.000040 0.112 0.014 0.00187 0.00036 0.282536 −1.4 1.39SJ2-zr12b 357 0.282648 0.000026 0.115 0.009 0.00171 0.00009 0.282637 2.1 1.16AlbernoaCO5zr2b 355 0.282656 0.000040 0.091 0.002 0.00186 0.00011 0.282643 2.3 1.15CO5zr4b 355 0.282645 0.000040 0.049 0.002 0.00093 0.00003 0.282639 2.2 1.16CO5zr5b 355 0.282616 0.000040 0.069 0.002 0.00132 0.00006 0.282607 1 1.23CO5zr6b 355 0.282597 0.000040 0.082 0.004 0.00167 0.00016 0.282586 0.3 1.28CO5zr8c 355 0.282582 0.000040 0.068 0.001 0.00137 0.00005 0.282573 −0.2 1.31CO5zr10c 355 0.282573 0.000040 0.058 0.009 0.00115 0.00011 0.282566 −0.4 1.32Serra BrancaSB8-89,7zr1b 357 0.282608 0.000040 0.065 0.004 0.00158 0.00015 0.282597 0.7 1.25SB8-89,7zr3b 357 0.282650 0.000040 0.056 0.006 0.00156 0.00015 0.282639 2.2 1.16ChançaCH601-zr19b 354 0.282554 0.000028 0.078 0.002 0.00127 0.00009 0.282546 −1.2 1.37CH601-zr26b 354 0.282596 0.000022 0.074 0.003 0.00115 0.00001 0.282588 0.3 1.27CH601-zr28b 354 0.282540 0.000022 0.060 0.003 0.00101 0.00010 0.282533 −1.6 1.4CH601-zr41b 354 0.282538 0.000022 0.060 0.004 0.00099 0.00009 0.282531 −1.7 1.4CH601-zr46 354 0.282640 0.000030 0.088 0.003 0.00137 0.00004 0.282631 1.9 1.18CH601-zr57 354 0.282599 0.000026 0.063 0.003 0.00096 0.00003 0.282593 0.5 1.26Lousal (PQ)LR23zr7b 626 0.282545 0.000040 0.077 0.004 0.00153 0.00011 0.282527 4.3 1.24LR23zr9b 2493 0.281023 0.000040 0.021 0.002 0.00044 0.00005 0.281002 −6.9 3.4

inh Pre-Variscan Inherited grain


At Serra Branca, three zircon grains from sample SB55, aquartz-feldspar-phyric porphyry, yielded a concordia age of366±2 Ma (Fig. 4e). A later stage at Serra Branca is markedby emplacement of microporphyry cryptodomes. A sampleof this micropophyry (sample SB8-89.7) yielded two zircongrains with a concordia age of 357±5 Ma (Fig. 4f).

In Chança, 24 concordant zircon grains provided an ageof 354±1 Ma for sample CH601 (Fig. 4g), while fourconcordant zircon grains provided an age of 349±5 Ma forsample CH602 (Fig. 4h).

In addition to the inherited, but still Variscan, zircongrains identified and discussed above, some samples con-tained pre-Variscan inherited grains, with Neo-Proterozoic,Paleo-Proterozoic and Archean ages (compiled in Fig. 5).The Late Archean inherited core at 2698±6 Ma fromsample SB54, has a rim which is strongly discordant alonga line to a lower intercept at ca. 365 Ma.

Finally, reconnaissance analyses of eight detrital zircongrains from the PQ Formation (sample LR23, from Lousal)yielded three Late Neo-Proterozoic ages and five Paleo-Proterozoic to Archean ages (Fig. 6). The Paleo-Proterozoicto Archean zircons are often orange to brown and rounded,in contrast to the clear or pale pink and more euhedral Neo-Proterozoic zircons.

Hafnium isotopes

The measured ratios are compiled in Table 3. Epsilonvalues were calculated using the chondritic values ofBouvier et al. (2007). Most of the present-day 176Hf/177Hf0ratios of the magmatic zircons fit a relatively narrow rangefrom 0.282394 to 0.282796, corresponding to ɛHf0 between−14.4 and −0.2, with an outlier at 0.282132 (ɛHf0=−23.7).A Paleo-Proterozoic detrital zircon grain from the PQFormation sample (LR23) has a present-day 176Hf/177Hf0ratio of 0.281023 (ɛHf0=−62.9), while an Late Neo-Proterozoic grain from the same formation has a present-day 176Hf/177Hf0 ratio of 0.282545 (ɛHf0=−9.1).

Initial isotope ratios, accommodating decay of 176Lu→176Hf,were estimated for the time of zircon crystallization,using the U–Pb ages (see above). The magmatic zirconshave initial 176Hf/177Hfi ratios within a narrow rangefrom 0.282384 to 0.282786, which corresponds to a ɛHfinterval between −6.8 and 7.4 (with the outlier at0.282129, or at ɛHf=−15.9). The PQ Formation LateNeo-Proterozoic detrital zircon has a 176Hf/177Hfi ratio of0.282527 (ɛHf=4.3), while the Paleo-Proterozoic detritalzircon has a 176Hf/177Hfi ratio of 0.281002 (ɛHf=−6.9).Figure 7 shows these results and how they relate with thechondritic uniform reservoir and with the depleted-mantlereservoir. The evolution of the depleted-mantle reservoirwas calculated using present-day values of 176Hf/177Hf0=0.283251 and 176Lu/177Hf0=0.0384 (Griffin et al. 2006).

Discussion

The magmatic zircon morphology, as established bycathodoluminescence studies, reflects the cooling of amagma of crustal origin, supporting the prevailing viewon the petrogenesis of IPB felsic volcanic rocks, whichsuggests that these rocks were formed by crustal fusioncaused by underplating and the invasion of the crust bymafic magmas (Munhá 1983; Mitjavila et al. 1997;Thiéblemont et al. 1998).

The U–Pb age estimates obtained for the magmaticzircons straddle the period between the Famennian (LateDevonian) and the Tournaisian (Early Carboniferous).These ages complement data reported by Nesbitt et al.(1999), Dunning et al. (2002) and Barrie et al. (2002). Asummary of all U–Pb data to date is presented in Fig. 8.This compilation indicates a duration of volcanism in theIPB of between 24 and 35 Ma, with volcanism lasting for atleast 7 Ma in a single location, as documented in Aljustrel.Clearly, the more data that are obtained, the more complex thesuccession of volcanic events will appear, both within a singlevolcanic edifice at each location and from one location to

0.2810

0.2815

0.2820

0.2825

0.2830

0.2835

0 0.2 0.4 0.6 0.8 1 1.2 1.40.35 0.4

Time (Ga)

0.2820

0.2830

0.2825

176 Hf

/177 Hf

(t)

176 Hf

/177 Hf

(t)

DM

CHUR

Fig. 7 Epsilon Hf data of magmatic zircons plotted against theirzircon U–Pb age, with CHUR and DM evolution lines (excluding pre-Variscan inherited grains). Dashed line is projection of the average

initial isotopic composition towards the DM line, via an intermediatereservoir with 176Lu/177Hf=0.015, which provides an average proto-lith age of ca. 1.4 Ga


another, at the basin scale. This warrants improved strati-graphic control. However, from all the results gathered to date,it appears that the volcanism has migrated within the basinperpendicularly to the suture from the present-day southwestto the northeast. The oldest volcanism is recorded in Cercal,while the volcanism in the Spanish sector of the Belt issignificantly younger, with remaining Portuguese areas regis-tering intermediate ages. This observation is not consistentwith a model of central uplift and intense volcanic activity nearwhat is now the Portuguese–Spanish border, with subsequentmigration of the already formed volcanic edifices towards thebasins’ margins, to the east and to the west, as suggested byBarrie et al. (2002). Instead, the inferred migration confirmsthe trend suggested by Carvalho (1976), based on thecompilation of paleontological dates for sediments enclosingthe volcanic rocks. However, this trend should not beassigned as the result of northward-dipping subduction tothe south of the Belt, as implied by Carvalho (1976), becauseample evidence linking the volcanism to extensional tectonicshas been published recently (see “Geochemistry and petrog-raphy of the volcanic rocks” above).

The two magmatic zircon generations, identified by CL, donot significantly vary in their initial Hf ratios. This indicatesthat no magma mixing from distinct sources occurred duringzircon crystallization. Protolith model ages for the magmaticzircons, calculated via an intermediate reservoir with anaverage Lu/Hf (176Lu/177Hf=0.015) as outlined in Andersenet al. (2002), provide ages which are predominantly Meso-Proterozoic, averaging 1.4 Ga (Table 3, Fig. 7). As expected,the higher epsilon values (more radiogenic) correspond to theyoungest ages and the lower epsilon values (less radiogenic)correspond to the oldest ages.

No possible juvenile crustal sources are known in theIPB. The base of the PQ Formation is not known and this

formation has a thickness of more than 2000 m (Tornos etal. 2005). Therefore, the PQ Formation may be considereda possible crustal source for the IPB acid magmas. The linkbetween the PQ Formation and metals in the massive sulfidedeposits has already been established by Jorge et al. (2007),based on lead isotope data. If the crustal source for the IPBacid magmas was the PQ Formation, or some othermetasedimentary rock assemblage, implying that there werecycles of erosion and sedimentation before fusion, the modelages should be interpreted with caution. This is becausesedimentary processes result in sediments with several crustalprovenances and fusion of such sediments generates melts inwhich the crystallizing zircons adopt Hf isotope ratios that aremixtures of the various sources involved. In this case, modelages may not necessarily indicate crust-formation events.Considering that the PQ Formation has detrital zirconpopulations with Late Neo-Proterozoic and also Paleo-Proterozoic to Archean ages, its fusion would yield magmaswith Hf crustal residence ages which are intermediate andconsistent with the data (i.e. Meso- Proterozoic). Also, thevolcanic rocks, while containing inherited zircons with LateNeo- Proterozoic and also Paleo-Proterozoic to Archean ages,also appear to lack inherited Meso-Proterozoic zircons, exactlyas recorded for the PQ Formation (Figs. 5 and 6). Hence thePQ Formation remains a likely source for the IPB magmas,although other unknown sources cannot be excluded.

Once formed, the acid magma has locally promotedremelting of older igneous rocks, as inferred from thepresence of inherited Variscan zircon grains in Aljustrelsamples. The recycling of recently-formed igneous rocksimplies a sustained heat flow which is favorable to thedevelopment of VMS deposits, such as the ones at Aljustrel.Therefore, the presence of recycled Variscan zircons isindicative of sustained heat flow and should be considered a

340

345

350

355

360

365

370

375

380

U-P

b A

ge

Caveira

Southwest Northeast

Cercal

Azinheira

de Barros

Lagoa

Salgada

Aljustrel

Albernoa

Serra Branca

Chança

Rio

Tinto

Nerva

Los

Frailes

Las

Cruces

Zufre

Fig. 8 Summary of U–Pb agedeterminations. Complementingdata presented in this study are;from Barrie et al. (2002) forLagoa Salgada, Aljustrel, RioTinto and Las Cruces, fromDunning et al. (2002) for Nervaand Zufre and from Nesbitt et al.(1999) for Los Frailes. Samesymbols as in Fig. 1


potential exploration criterium for VMS deposits. Thisshould be coupled with zircon saturation temperatureinformation, as outlined by Rosa et al. (2006).

Conclusions

The zircon morphology indicates that the IPB acid magmaswere of crustal origin. The Hf protolith model ages, which werecalculated using magmatic zircon from the Volcano SiliceousComplex are intermediate between the zircon U–Pb agepopulations recorded in the sample of the Phyllite-QuartziteFormation, consistent with the hypothesis that this formationwas the source for the IPB acid magmas. This is furthersupported by the absence of inherited Meso-Proterozoiczircons in the volcanic rocks. The acid magmas weresubsequently emplaced from the Famennian through theTournaisian. When compared with the previously publishedage data, it appears that volcanism migrated perpendicularlyto the suture, i.e. southwest to the northeast of the IPB basin(present day coordinates).

Acknowledgements This work was sponsored by an InternationalIncoming Short Visits grant from the Royal Society, by an EFTAGrant and by the POCTI program of the Fundação para a Ciência eTecnologia (Portugal). This work is a contribution of DRN Rosatowards FCT project POCI/CTE-GIN/56450/2004 “PYBE-Towards aBetter Understanding of the Pyrite Belt Basin Evolution”. The authorswould like to acknowledge Donald Herd (University of St Andrews)and Berit Løken Berg, Gunborg Bye-Fjeld and Jarkko Lamminen(University of Oslo) for assistance with sample preparation andcharacterization and Siri Simonsen (University of Oslo) for herassistance during LA-ICP-MS work. Further laboratory support wasprovided by the CREMINER-Centro de Recursos Minerais, Miner-alogia e Cristalografia, at the University of Lisbon. DRN Rosa wouldlike to acknowledge the fruitful discussions with João Matos, JoséTomás Oliveira and Carlos Rosa.

Appendix

084

044

004

063

023

082

40.0

50.0

60.0

70.0

80.0

. 26085.045.0. 05064.0. 24083.034.003.0702 /bP 532 U

206 P

b/23

8 U

2-aromeT

aidrocnoC aM 1.1± 2.814 = egA

2( σ , )derongi srre .tsnoc-yaced

DWSM ,7800.0 = )ecnadrocnoc fo(

ytilibaborP 39.0 = )ecnadrocnoc fo(

04=n

PlesoviceaidrocnoC aM 7.0± 3.933 = egA

2( σ, )derongi srre .tsnoc-yaced

DWSM ,71.1 = )ecnadrocnoc fo(

ytilibaborP 82.0 = )ecnadrocnoc fo(

85=n

^

Fig. 9 Reference zircons Temora-2 (TIMS-ID U–Pb age: 416.8±1.3 Ma; Black et al. 2004) and Plešovice (TIMS-ID U–Pb age: 337.1±0.4 Ma; Sláma et al. 2008) measured as unknowns

0.2819

0.2821

0.2823

0.2825

0.2827

0.2829

0.120.100.080.060.040.020.00

176Yb/177Hf

(laitini) fH771/fH671

-aromeT

Mud Tank

GJ-

91500

Fig. 10 Hf isotopic composi-tion of reference samples MudTank, Temora-2, 91500 and GJ-1 measured as unknowns duringa 2 year period


Tab

le4

U–P

bdata

forstandard

zircon

sTem

ora-2andPlešovice

measuredas

unkn

owns

Sam

ple

Analysisid.

Upp

m206Pb

206/20

4207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/

238U*

1SE

Rho

207Pb/

206Pb

age(M

a)2σ

207Pb/235U

age(M

a)2σ

206Pb/238U

age(M

a)2σ

Calibratio

nstandards

Tem

ora2

TEM-01

483.2

341

0.05

600.00

060.51

370.00

730.06

670.00

080.56

450

4842

110

416

10GJ-1,

9150

0Tem

ora2

TEM-02

523.4

856

0.05

570.00

070.51

590.00

730.06

720.00

080.41

442

4842

210

419

10GJ-1,

9150

0Tem

ora2

TEM-03

573.7

792

0.05

570.00

060.51

710.00

640.06

740.00

080.43

442

4442

38

420

10GJ-1,

9150

0Tem

ora2

TEM-05

139

8.8

2514

0.05

540.00

050.50

910.00

630.06

670.00

080.33

430

4441

88

416

10GJ-1,

9150

0Tem

ora2

TEM-06

137

8.7

1901

0.05

550.00

050.50

950.00

600.06

670.00

080.61

432

3641

88

416

10GJ-1,

9150

0Tem

ora2

TEM-07

895.5

1176

0.05

490.00

060.49

920.00

660.06

610.00

080.22

408

44411

841

310

GJ-1,

9150

0Tem

ora2

TEM-08

122

7.6

2170

0.05

490.00

050.50

550.00

630.06

690.00

090.60

410

4041

58

417

10GJ-1,

9150

0Tem

ora2

TEM-09

203

12.6

3592

0.05

480.00

050.51

520.00

710.06

830.00

100.85

406

3842

210

426

12GJ-1,

9150

0Tem

ora2

TEM-04

654.1

919

0.05

550.00

060.51

080.01

300.06

700.00

180.22

431

4241

918

418

22GJ-1,

9150

0Tem

ora2

TEM-01

956.2

1040

0.05

520.00

050.50

690.01

230.06

660.00

170.33

422

4241

616

416

20GJ-1,

9150

0Tem

ora2

TEM-02

785

4386

0.05

550.00

060.50

710.01

250.06

630.00

170.24

433

4641

616

414

20GJ-1,

9150

0Tem

ora2

TEM-03

249

15.7

1212

10.05

520.00

050.51

300.01

280.06

760.00

180.27

421

3842

018

422

22GJ-1,

9150

0Tem

ora2

TEM-006

113

7.3

1356

0.05

520.00

100.51

860.00

560.06

840.00

080.60

421

8242

48

427

10GJ-1,

9150

0Tem

ora2

TEM-004

553.5

1305

0.05

530.00

110.51

600.00

560.06

780.00

070.31

424

8642

28

423

8GJ-1,

9150

0Tem

ora2

TEM-01

623.9

561

0.05

520.00

060.50

470.00

660.06

640.00

080.58

420

4841

58

414

10GJ-1,

9150

0Tem

ora2

TEM-02

674.2

693

0.05

600.00

060.51

370.00

660.06

660.00

080.34

452

5042

18

416

10GJ-1,

9150

0Tem

ora2

TEM-03

462.8

745

0.05

610.00

070.50

920.00

720.06

600.00

080.51

457

5241

810

412

10GJ-1,

9150

0Tem

ora2

TEM-04

633.9

1000

0.05

550.00

060.51

580.00

690.06

750.00

080.29

434

5042

210

421

10GJ-1,

9150

0Tem

ora2

TEM-001

835.3

1158

0.05

520.00

060.51

740.00

410.06

800.00

040.61

422

4642

36

424

6GJ-1,

9150

0Tem

ora2

TEM-002

946.1

3963

90.05

510.00

060.51

570.00

390.06

800.00

030.15

414

4842

26

424

4GJ-1,

9150

0Tem

ora2

TEM-004

116

7.5

1411

0.05

540.00

060.51

550.00

400.06

760.00

030.24

426

4642

26

422

4GJ-1,

9150

0Plešovice

PL-02

718

39.1

1748

50.05

330.00

020.39

430.00

480.05

370.00

060.34

341

2033

88

337

8GJ-1

Plešovice

PL-03

599

32.2

7553

0.05

260.00

020.38

400.00

480.05

300.00

060.53

311

1833

08

333

8GJ-1

Plešovice

PL-04

479

25.7

4916

0.05

280.00

030.38

460.00

490.05

290.00

060.45

319

2233

08

332

8GJ-1

Plešovice

PL-05

351

18.9

3215

0.05

400.00

030.39

410.00

510.05

300.00

060.42

370

2233

78

333

8GJ-1

Plešovice

PL-06

470

25.3

2305

0.05

300.00

020.38

710.00

490.05

300.00

060.24

328

2033

28

333

8GJ-1

Plešovice

PL-07

665

36.8

2140

70.05

320.00

020.39

790.00

520.05

430.00

070.49

337

1834

08

341

8GJ-1

Plešovice

PL-08

545

30.1

4586

0.05

430.00

020.40

500.00

530.05

410.00

070.55

385

2034

58

339

8GJ-1

Plešovice

PL-09

559

31.1

2638

0.05

330.00

030.39

930.00

540.05

430.00

070.30

342

2034

18

341

8GJ-1

Plešovice

PL-10

652

36.7

3483

30.05

320.00

020.40

280.00

550.05

490.00

070.59

336

2034

48

345

8GJ-1

Plešovice

PL-01

566

3118

392

0.05

390.00

030.40

190.00

500.05

410.00

060.53

368

2034

38

339

8GJ-1

Plešovice

PL-01

723

39.3

3957

30.05

350.00

020.39

370.00

450.05

340.00

050.51

350

1833

76

335

6GJ-1

Plešovice

PL-02

720

3943

400.05

360.00

020.39

330.00

450.05

320.00

050.45

355

1833

76

334

6GJ-1

Plešovice

PL-03

642

34.9

6693

0.05

340.00

020.39

310.00

470.05

340.00

050.53

345

2033

76

335

6GJ-1

Plešovice

PL-04

500

27.5

5210

0.05

360.00

030.39

850.00

480.05

390.00

050.32

353

2234

16

339

6GJ-1

Plešovice

PL-03

598

32.2

6693

0.05

330.00

020.38

910.00

320.05

290.00

030.53

343

2033

44

332

4GJ-1

Plešovice

PL-04

465

25.3

5210

0.05

350.00

030.39

420.00

330.05

340.00

030.32

351

2233

74

336

4GJ-1

Plešovice

PL-05

712

38.9

5926

0.05

290.00

020.39

120.00

320.05

360.00

040.60

324

1833

54

337

4GJ-1

Plešovice

PL-07

499

27.4

4971

0.05

300.00

020.39

440.00

330.05

390.00

030.40

330

1833

84

339

4GJ-1

Plešovice

PL-08

507

27.9

6763

0.05

330.00

020.39

680.00

330.05

400.00

040.49

342

2033

94

339

4GJ-1


Tab

le4

(con

tinued)

Sam

ple

Analysisid.

Upp

m206Pb

206/20

4207Pb/206Pb*

1SE

207Pb/235U*

1SE

206Pb/

238U*

1SE

Rho

207Pb/

206Pb

age(M

a)2σ

207Pb/235U

age(M

a)2σ

206Pb/238U

age(M

a)2σ

Calibratio

nstandards

Plešovice

PL-01

679

37.4

3621

0.05

290.00

050.39

450.00

740.05

410.00

110.49

324

4233

810

340

14GJ-1

Plešovice

PL-02

722

39.5

9095

0.05

260.00

050.38

960.00

730.05

380.00

110.53

310

4233

410

338

14GJ-1

Plešovice

PL-03

996

54.5

9199

0.05

260.00

050.38

960.00

730.05

370.00

110.66

313

4033

410

337

14GJ-1

Plešovice

PL-04

859

46.4

7668

0.05

270.00

050.38

600.00

720.05

320.00

110.75

315

4233

110

334

14GJ-1

Plešovice

PL-05

695

37.2

1015

40.05

300.00

050.38

360.00

730.05

250.00

110.59

328

4233

010

330

12GJ-1

Plešovice

PL-06

683

36.7

3863

0.05

300.00

050.38

530.00

730.05

280.00

110.50

328

4233

110

331

14GJ-1

Plešovice

PL-07

920

49.2

7260

0.05

300.00

050.38

390.00

730.05

250.00

110.72

329

4233

010

330

12GJ-1

Plešovice

PL-08

938

50.1

5484

0.05

310.00

050.38

420.00

730.05

250.00

110.68

331

4233

010

330

12GJ-1

Plešovice

PL-09

756

4240

350.05

240.00

050.39

350.00

760.05

450.00

110.75

301

4233

712

342

14GJ-1

Plešovice

PL-10

883

49.6

5387

0.05

240.00

050.39

800.00

760.05

510.00

110.44

302

4234

012

346

14GJ-1

Plešovice

PLZ-02

706

36.5

8902

0.05

330.00

100.39

230.00

500.05

350.00

070.85

340

7833

68

336

8GJ-1

Plešovice

PL-03

441

2374

000.05

300.00

100.39

630.00

550.05

440.00

070.47

330

8233

98

342

8GJ-1

Plešovice

PLZ-01

617

3222

499

0.05

310.00

100.39

240.00

500.05

370.00

070.74

334

8033

68

337

8GJ-1

Plešovice

PL-01

348

18.9

2315

0.05

260.00

040.39

950.00

440.05

520.00

070.33

313

3634

16

346

8GJ-1,

9150

0Plešovice

PL-02

400

21.3

4682

0.05

330.00

040.39

860.00

430.05

430.00

060.22

343

3634

16

341

8GJ-1,

9150

0Plešovice

PL-03

396

2110

329

0.05

310.00

040.40

160.00

430.05

500.00

070.58

333

3834

36

345

8GJ-1,

9150

0Plešovice

PL-05

721

37.2

5712

0.05

320.00

040.39

900.00

430.05

450.00

070.26

339

3634

16

342

8GJ-1,

9150

0Plešovice

PL-07

809

40.9

4131

0.05

270.00

040.39

440.00

440.05

440.00

070.11

316

3633

86

342

8GJ-1,

9150

0Plešovice

PL-08

719

36.2

2937

0.05

310.00

040.39

540.00

440.05

410.00

070.28

334

3433

86

340

8GJ-1,

9150

0Plešovice

PL-09

717

36.2

4188

0.05

260.00

040.39

990.00

480.05

530.00

070.16

313

3434

26

347

8GJ-1,

9150

0Plešovice

PL-10

674

34.1

7992

0.05

260.00

040.40

050.00

490.05

540.00

070.41

311

3434

28

348

8GJ-1,

9150

0Plešovice

PL-01

421

22.4

2745

0.05

340.00

050.40

160.00

950.05

460.00

130.50

347

3834

314

343

16GJ-1,

9150

0Plešovice

PL-02

568

30.2

4160

0.05

330.00

050.40

050.00

940.05

460.00

130.69

339

3834

214

343

16GJ-1,

9150

0Plešovice

PL-03

553

28.2

3906

90.05

300.00

050.39

930.00

970.05

490.00

140.37

328

3834

114

344

16GJ-1,

9150

0Plešovice

PL-04

642

32.7

9923

0.05

330.00

050.40

090.00

980.05

480.00

140.71

343

3834

214

344

18GJ-1,

9150

0Plešovice

PL-05

795

40.7

4961

0.05

330.00

050.40

340.00

990.05

520.00

140.81

340

3634

414

346

18GJ-1,

9150

0Plešovice

PL-001

380

19.5

4732

0.05

350.00

100.40

460.00

350.05

500.00

060.42

349

8634

56

345

6GJ-1,

9150

0Plešovice

PL-002

598

30.9

3300

10.05

320.00

100.40

400.00

340.05

520.00

060.45

337

8234

54

346

6GJ-1,

9150

0Plešovice

PL-003

702

35.9

6599

0.05

320.00

100.39

580.00

350.05

420.00

060.50

337

8233

96

340

8GJ-1,

9150

0Plešovice

PL-004

655

33.4

6640

0.05

300.00

100.39

270.00

350.05

410.00

060.63

326

7833

66

340

8GJ-1,

9150

0Plešovice

PL-01

613

31.9

5198

0.05

310.00

050.39

960.00

430.05

470.00

060.40

333

4034

16

343

8GJ-1,

9150

0Plešovice

PL-02

580

30.1

3735

0.05

330.00

050.39

980.00

430.05

450.00

060.11

342

4034

16

342

8GJ-1,

9150

0Plešovice

PL-03

541

27.2

5570

0.05

340.00

050.40

030.00

450.05

450.00

060.49

346

4034

26

342

8GJ-1,

9150

0Plešovice

PL-04

607

30.6

2433

30.05

330.00

050.40

050.00

450.05

460.00

060.31

343

4034

26

343

8GJ-1,

9150

0Plešovice

PL-05

536

26.9

6715

0.05

320.00

050.40

610.00

490.05

550.00

070.32

339

4234

68

348

8GJ-1,

9150

0Plešovice

PL-06

533

26.5

4854

0.05

350.00

050.40

450.00

490.05

510.00

070.35

349

4034

58

345

8GJ-1,

9150

0Plešovice

PL-001

a68

135

.486

530.05

340.00

050.40

400.00

240.05

500.00

030.52

344

4434

54

345

4GJ-1,

9150

0Plešovice

PL-004

628

32.3

1239

70.05

310.00

050.39

730.00

250.05

430.00

030.50

334

4434

04

341

4GJ-1,

9150

0Plešovice

PL-006

572

29.1

4789

0.05

310.00

050.39

320.00

270.05

380.00

030.54

335

4233

74

338

4GJ-1,

9150

0


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Table 5 Summary of Yb-Lu-Hf systematics of reference zircons

Reference sample Present day Initial

N 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 178Hf/177Hf t (Ma) (176Hf/177Hf)t ɛHf

JMC475a 18 0.282158 1.467292 SD 0.000028 0.00006

91500 129 0.0120 0.0003 0.282301 1.46728 1065 0.282295 6.02 SD 0.0043 0.00005 0.000080 0.00018 0.000079 2.8

Mud tank 509 0.0015 0.00003 0.282509 1.46727 732 0.282509 6.02 SD 0.0010 0.00002 0.000050 0.00010 0.000050 1.8

Temora 2 273 0.0457b 0.0011 0.282701 1.46726 417 0.282692 5.42 SD 0.0344 0.0007 0.000062 0.00013 0.000061 2.2

GJ-1 115 0.0096 0.00028 0.282018 1.46727 608 0.282015 -14.22 SD 0.0024 0.00002 0.000062 0.00012 0.000062 2.2

Literature values (solution data): 91500: 0.282306±8, Mud Tank: 0.282507±6, Temora-2: 0.285686±8 (Woodhead and Hergt 2005); GJ-1:0.281998±7 (Gerdes and Zeh 2006)a Pure solution analyzed using Nu Instruments desolvating nebulizer.b Observed range of 176 Yb/177 Hf in Temora-2: 0.0136 to 0.0922.


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U–Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian Pyrite Belt

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