The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the Southwest Central Iberian Zone: constraints from detrital zircon data on northern Gondwana margin evolution during the late Neoproterozoic

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ContentslistsavailableatSciVerseScienceDirect

Precambrian

Research

j o u r n al hom ep age :w w w . e l s e v i e r . c o m / l o c a t e / p r e c a m r e s

The

provenance

of

Late

Ediacaran

and

Early

Ordovician

siliciclastic

rocks

in

the

Southwest

Central

Iberian

Zone:

Constraints

from

detrital

zircon

data

on

northern

Gondwana

margin

evolution

during

the

late

Neoproterozoic

M.F.

Pereira

a,∗

_,

_U.

_Linnemann

b

_,

_M.

_Hofmann

b

_,

_M.

_Chichorro

c

_,

_A.R.

_Solá

d

_,

_J.

_Medina

e

_,

_J.B.

_Silva

f

a_IDL,_Departamento_de_{Geociências,}_ECT,_Universidade_de_Évora,_Apartado_94,_7001-554_Évora,_Portugal b_Senckenberg_{Naturhistorische}_Sammlungen_Dresden,_Germany

c_CICEGe,_Faculdade_de_Ciências_e_Tecnologia,_Universidade_Nova_de_Lisboa,_Quinta_da_Torre,_2829-516_Caparica,_Portugal d_LNEG,_Unidade_de_Geologia_e_Cartograﬁa_Geológica,_Portugal

e_Departamento_de_{Geociências,}_Universidade_de_Aveiro,_Portugal f_IDL,_Departamento_de_Geologia,_FCUL,_Portugal

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received7February2011

Receivedinrevisedform14October2011 Accepted28October2011

Available online xxx Keywords: Provenanceanalysis NorthernGondwanamargin Avalonian–Cadomianmagmaticarc Central-IberianZone

WestAfrican Amazoniancratons

a

b

s

t

r

a

c

t

U–PbgeochronologyofdetritalzirconfromLateEdiacaran(BeirasGroupgreywackes)andEarly Ordovi-cian(SarnelhasarkosicquartzitesandArmoricanquartzitesof Penacova)sedimentaryrocksofthe southwestCentralIberianZone(SWCIZ)constraintheevolutionofnorthernGondwanaactive-passive margintransition.TheLA-ICP-MSU–Pbdataset(375detritalzirconswith90–110%concordantages)is dominatedbyNeoproterozoicages(75%forthegreywakesand60%forthequartzites),amongwhichthe mainagecluster(moresignificantforBeirasGroupgreywackes)isCryogenian(c.840–750Ma),whilea fewMesoproterozoicandTonianagesarealsopresent(percentages<8%).Thesetwofeatures,andthe predominanceofCryogenianagesoverEdiacaranages,distinguishtheBeirasGroupgreywackes(SW CIZ)fromthetime-equivalentSerieNegra(Ossa-MorenaZone–OMZ),withwhichtheyareininferred contact.TheagespectraoftheBeirasGroupgreywackesalsorevealthreemajorepisodesofzircon crys-tallisationinthesourceareaduringtheNeoproterozoicthatareprobablyassociatedwithalong-lived systemofmagmatismthatdevelopedeitheralongorinthevicinityofthenorthernGondwanamargin at:(1)c.850–700Ma–Pan-Africansuture(notwellrepresentedinOMZ);(2)c.700–635Ma–early Cadomianarc;and(3)c.635–545Ma–lateCadomianarc.ComparisonofNeoproterozoicagesandthose ofthePaleoproterozoic(c.2–1.8Ga)andArchean(mainlyNeoarchean–2.8–2.6Ga,butalsoolder)inthe BeirasGroupgreywackeswithU–PbagesofCadomiancorrelativesshowsthat:(1)SWCIZ,OMZ, Saxo-ThuringianZone,NorthArmoricanCadomianBeltandAnti-Atlas)evolvedtogetherduringtheformation ofback-arcbasinsonthenorthernGondwanaactivemarginand(2)allrecordedsynorogenicbasinsthat werefilledduringtheEdiacaranbydetritusresultingfromerosionoftheWestAfricancraton,the Pan-Africansutureandalong-livedCadomianmagmaticarc.Differencesindetritalzirconagepopulationsin thegreywackesoftheBeirasGroup(SWCIZCadomianbasement)andtheSerieNegra(OMZCadomian basement)arealsoobservedintheirrespectiveoverlyingEarlyOrdovicianquartzites.Sinceboththese SWIberiaCadomianbasementsevolvedtogetheralongtheactivemarginofGondwana(butsufficiently separatedtoaccountforthedifferencesintheirdetritalzirconcontent),thiscontinuationofdiffering zirconpopulationsintotheEarlyOrdoviciansuggeststhattheinferredcontactpresentlyjuxtaposing theBeirasGroupandtheSerieNegraisnotpre-EarlyOrdovicianandsoisunlikelytodemonstratea Cadomiansuture.

1. Introduction

The basement rocks of Western and Central Europe were

formedduringtheﬁnalstagesofGondwanaassemblyinthelate

∗ Correspondingauthor.

E-mailaddress:mpereira@uevora.pt(M.F.Pereira).

Neoproterozoic(MurphyandNance,1991;Linnemannetal.,2004)

(Figs.1Aand2).Inthiscontext,Iberiaoccupiesacriticalrolein

enabling anunderstandingof theevolution ofa LateEdiacaran

activemargininNorthGondwanaandthesubsequenttransition

toapassivemargininCambrian–Ordoviciantimes(Murphyetal.,

2006a,b;Linnemannetal.,2008;Nanceetal.,2008,2010).Overthe

lasttwodecades,advancesinourknowledgeofstratigraphy,

defor-mation,geochemistry,isotopechemistryandgeochronologyhave

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M.F.Pereiraetal./PrecambrianResearch192–195 (2012) 166–189 167

Fig.1. (A)MapshowingthelocalitieswheretheNorthGondwanaterranesarepreservedinNorthAmerica,EuropeandNorthAfrica.(B)SimpliﬁedgeologicalmapofIberia showinglocationofthelateNeoproterozoicrocks.(C)Simpliﬁedgeologicalmap,crosssectionandstratigraphiccolumnofthePenacovasyncline.Samplelocationsusedfor U–Pbanalyses,fromtheSWCIZlateNeoproterozoicandEarlyOrdovicianrecord.

beenconstrained bylinkagesbetweenperi-Gondwananarc

cor-relativesofNorthAmerica,EuropeandNorthAfricawiththeaim

ofdecipheringtheirpaleogeographicpositionsrelativetopotential

sedimentaryprovenances(Murphyetal.,1996,2002,2004;Ugidos

etal.,1997,2003;Fernández-Suarezetal.,2002;Nanceetal.,2002, 2008;Linnemannetal.,2004,2008;Gutierrez-Alonsoetal.,2003; Pereiraetal.,2006,2008a;Abatietal.,2010)(Fig.2).

InIberia,thelateNeoproterozoicrecordisexposedin

differ-enttectono-stratigraphiczones(Julivertetal.,1974;Franke,1989),

fromNorthtoSouth(Fig.1B):theCantabrianZone(CZ),theWest

AsturianLeoneseZone(WALZ),theCentralIberianZone(CIZ)and

theOssa-MorenaZone(OMZ).Themostlyextensiveexposuresof

LateEdiacaranagethatoccurintheWALZ,CIZ andintheOMZ

andaredominatedbysedimentaryrocksandwithrelativelyminor

igneousrocks(Fernández-Suarezetal.,2000;Eguíluzetal.,2000;

Gutierrez-Alonsoetal.,2003;Rodriguez-Alonsoetal.,2004;Pereira etal.,2006,2008b).

Iberia’sgeographicpaleopositionduringthelate

Neoprotero-zoicisgenerallyindicated bythepresence orabsenceof

Meso-proterozoic(c.1Ga)detritalzirconagesfoundinLateEdiacaran

sedimentaryrocks.NeoproterozoicsedimentaryrocksinNWIberia

(WALZ)showasigniﬁcantpercentage(11–37%)of

Mesoprotero-zoicdetrital zirconages suggestinga paleopositionclosetothe

AmazoniancratonandAvaloniancorrelatives(Fernández-Suarez

etal.,2000,2002;Gutierrez-Alonsoetal.,2003).Ontheotherhand,

thelack or insigniﬁcantpercentage of Mesoproterozoicages in

SWIberia(OMZ)providesevidenceforaperi-WestAfricancraton

paleoposition nearto Cadomian correlatives (Fernández-Suarez

etal., 2002;Gutierrez-Alonsoetal., 2003;Pereiraet al.,2008a; Linnemannetal.,2008).HowevertheNeoproterozoiclocationof

Iberiaisstillcontroversial,andrecentlyDiezFernandezetal.(2010)

proposedanalternativehypothesissuggestingIberiawaslocated

tothenorthoftheWestAfricancratonclosetotheTrans-Sahara

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Fig.2. SchematicpaleogeographicalmapoftheGondwanasupercontinentatc.570–560MawithpossiblepaleopositionofIberia. ModiﬁedfromLinnemannetal.(2004)andreferencestherein.

This paper presents new U–Pb LA-ICP-MS geochronology

of detrital zircons from Ediacaran greywackes and Ordovician

quartzitesofakeystratigraphicsuccessioninthesouthwestofthe

CIZ(Penacova,Portugal)closetotheCIZ-OMZtransition(Fig.1Band

C).OurﬁndingsshowthepredominanceofNeoproterozoicages

(60–77%),providing important information aboutolder

zircon-formingevents(inparticular,EdiacaranandCryogenian)thathelp

tocharacterisepotentialsedimentaryprovenances.Takingasour

referenceU–PbzirconagespublishedfordifferentareasofNorth

Gondwanaoverthelasttwentyyears,wediscusspotential

sed-imentary sources for the Iberia Ediacaran basement that may

include(Nanceetal.,2008andreferencestherein):(1)NorthAfrica

(WestAfrican cratonand Trans-Saharabelt),(2) SouthAmerica

(AmazoniancratonandTrans-Brasilianobelt),and(3)

Neoprotero-zoicperi-Gondwananarc terranesofNorthAmericaandEurope

(Avalonia and Ganderialocatedin proximity totheAmazonian

cratonorCadomialinkedtotheWestAfricancraton)(Fig.2).

In addition,a comparison is alsomade withavailable U–Pb

geochronologicaldatafromLateEdiacaranandEarlyOrdovician

sedimentary rocks of SW Iberia, NW Iberia, Cadomia and the

Anti-Atlasin order to: (1) decipher the paleoposition of Iberia

along the northern Gondwana margin, in the context of the

Avalonian–Cadomianand/orPan-Africanorogenies;(2)test

possi-bleconnectionsbetweenEuropeanandNorthAfricancorrelatives;

and(3)provideadditionalinsightsintonorthernGondwana

mar-ginassemblyandbreakupduringlateNeoproterozoicandearly

Paleozoictimes.

2. Geologicalsetting

TheCIZisamajorsubdivisionofIberia(Julivertetal.,1974)

thatextendsfromtheboundarywiththeWALZ(NWIberia)toSW

intheCIZ-OMZtransition.IntheCIZ-OMZtransition,Early

Ordovi-cianrockswithapaleogeographicafﬁnitytotheCIZunconformably

overlietheOMZCadomianbasement(SérieNegra;Pereiraetal.,

2006;Linnemannetal.,2008;Soláetal.,2008)(Fig.1B).TheCIZ

includesEarlyOrdovicianquartzitesthatunconformablyoverlie

EdiacaranandCambrianrocksoftheSchist–GreywackeComplex

(Carrington da Costa, 1950; Schermerhorn, 1955; Sousa, 1982)

alsocalled“SupergrupoDurico-Beirão”(Silvaetal.,1987–1989;

SousaandSequeira,1987–1989;SequeiraandSousa,1991).The

Schist–GreywackeComplexincludestheBeirasandDouroGroups,

whichconsistofNeoproterozoictoearlyCambriansedimentary

rocks(Medinaetal.,1998).TheearlyOrdovicianquartzitesthat

directlyoverlietheBeirasGroupoccurinNW–SE-trendinglimbs

ofVariscankilometre-scalefoldsontheGeologicalMapofPortugal

(1992,2010).

ThePenacovaridgelocatedintheSEextremityoftheBuc¸aco

mountainrange isa 130–140◦ trendingsyncline witha steeply

(70–80◦)dipping axial plane(Fig. 1C). Cambrian rocks are not

presentinthePenacovastratigraphythatincludesfromthebase

to the top: (1) the Beiras Group with greywackes and slates

(LateEdiacaran;Medinaetal.,1998);(2)theSarnelhasFormation

(LateCambrian–EarlyOrdoviciantransition;“Grauwackesrouges

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CarringtondaCosta,1950)includingarkosicquartzites;and(3)the

ArmoricanQuartziteFormation(EarlyOrdovician;Oliveiraetal.,

1992).

The BeirasGroup slates and greywackes (SW CIZ Cadomian

basement)weretiltedbeforethedepositionofthearkosicbeds

of the Sarnelhas Formation. In thenorthern limb of the

Pena-covasyncline(Fig.1C),steeplyNNE-dippingoverturnedbedsof

slatesandgreywackesoftheBeirasGroupareoverlainbysteeply

SW-dippingbedsof Ordovicianquartzites, slates and

metacon-glomerates,deﬁning a major angular unconformityat thebase

of the Ordovician sequence. In Penacova, the sedimentological

featuresoftheBeirasGroupsuggestasiliciclasticplatformal

depo-sitional environment characterised by sand bars inﬂuenced by

stormevents(Medinaetal.,1998).ThesteeplyNEE-dippingand

overturnedBeira Groupsuccessionis characterisedby

alternat-ingmetre-andcentimetre-scalebedsofmedium-toﬁne-grained

sandstones,and bandedsilty toclayey sedimentaryrocks with

interbeddedconglomerates.ThesectionoftheBeirasGroup

exam-inedincludes,fromthebasetothetop(Medina,1996;Fig.1C):

(1) thick beds of coarse- to medium-grained sandstones with

parallelbeddingandlow-anglecross-bedding,separatedby

mud-supportedconglomerates(withcentimetre-scaleroundedpebbles

of quartz, clasts of volcanic and sedimentary rocks, including

roundedpebblesofblackcherts); (2)interbeddedthinlayersof

ﬁne-grained sandstone withsilt mudstones showingwavy and

lenticularlamination,andripples;(3)coarse-tomedium-grained

greywackes,sandstoneswithparallelbeddingandlow-angle

cross-bedding,alsoshowingchannelgeometriesandincludingfragments

of mudstones and trace fossils from the Late Ediacaran (Vidal

etal., 1994;Pereira etal., 2008b);(4)interbedded ﬁne-grained

sandstonesandgrey-blackmudstoneswithhummockystructures,

ripplesandwavylamination;and(5)grey-blackmudstoneswith

fewintercalationsofsandstones.TheearlyPaleozoicsequencethat

unconformablyoverliestheBeirasGroupsedimentaryrocks

con-sistsofbasal LateCambrian–EarlyOrdovicianarkosicquartzites

andslateswithintercalationsofconglomerates(Sarnelhas

Forma-tion).TheSarnelhasarkosicquartzitesshowparallellamination,

cross-bedding,channelgeometriesandripples.TheSarnelhas

For-mationisoverlainbytheArmoricanQuartziteFormation(Early

Ordovician)which includesmassivebedsof quartzitesand thin

layersofslates.TheearlyPaleozoicsequenceischaracteristicof

shallowmarinesiliciclasticplatformsedimentation.Theangular

unconformitywithEarlyOrdovicianrockslyingdirectlyovertilted

Ediacaranstratadevelopedasresultofamajorcrustalextensionin

theCambrian–Ordovician(Pereiraetal.,2008b).

The Ediacaran and Ordovician sedimentary rocks were

deformed under low-grade metamorphic conditions (Variscan

deformation).TheLateEdiacaransuccessionexhibitsa135–145◦

trendingcrenulationcleavagesuperposedtotighttoopenclosed

foldswithgentlyE-plungingaxis,and110–120◦trendingand

NNE-dipping(62–66◦)spaced orpenetrativeroughtoslatycleavage,

whereastheOrdoviciansequenceshowsclosedtoopenfoldswith

gentlyplungingfoldaxesand135–145◦trendingspacedfractured

cleavageorslatycleavage.

3. U–PbLA-ICP-MSgeochronology

3.1. Samplesandmethods

Foursampleswerecollectedforthisgeochronologystudy

(coor-dinatesdatumWGS84inTables1–4):PNC1andPNC2represent

twogreywackesfromtheBeirasGroup,PNC3isanarkosicquartzite

fromtheSarnelhasFormation,andPNC4isaquartzitefromthe

ArmoricanQuartziteFormation. LensandCL-imaging ofzircons

arepresentedinFigs.3and4andtheresultsobtainedfromU–Pb

geochronologyinFigs.5–8andTables1–4.

Zircon grains were extracted, then mounted in epoxy

resin with zircon standards SL13 (U=238ppm) and TEMORA

(206_Pb*/238_U₌_0.06683)._The_polished_mounts_were_photographed

andthentwoofthem(samplesPNC2andPNC3)wereimagedby

SEMcathodoluminescence(CL)todocumenttheinternalgrowth

zoningofthegrains.ZircongrainswerethenanalysedforU,Th,and

PbisotopesbyLA-ICP-MS(LaserAblationwithInductivelyCoupled

PlasmaMassSpectrometry)attheMuseumfürMineralogieund

Geologie (SenckenbergNaturhistorische SammlungenDresden),

usingaThermo-ScientiﬁcElement2XRsectorﬁeldICP-MScoupled

toaNewWaveUP-193ExcimerLaserSystem.Ateardrop-shaped,

low-volumelasercellwasusedtoenablesequentialsamplingof

heterogeneous grains (e.g. growth zones) during time-resolved

dataacquisition.Eachanalysisconsistedof15sbackground

acqui-sitionfollowedby35sdataacquisition,usinglaser-spotsizesof

15–35␮m.A common-Pbcorrectionbased onthe

interference-andbackground-corrected204_Pb_signal_and_a_model_Pb

composi-tion(StaceyandKramers,1975)wascarriedoutwherenecessary.

Thecriterionforcorrectionwaswhetherthecorrected207_Pb/206_Pb

layoutsidetheinternalerrorofmeasuredratios.Time-resolved

sig-nalsoftheLA-ICP-MSwerecheckedinordertodetectdisturbances

caused by cracksor mineral inclusions.In suchcases, analyses

wereexcludedfromagecalculations.Rawdatawascorrectedfor

background signals, common Pb, laser-induced elemental

frac-tionation,instrumentalmassdiscrimination,andtime-dependent

elementalfractionationofPb/ThandPb/UusinganExcel®

spread-sheetprogramdevelopedbyAxelGerdes(InstituteofGeosciences,

JohannWolfgangGoethe-UniversityFrankfurt,FrankfurtamMain,

Germany).Reporteduncertaintieswerepropagatedbyquadratic

additionoftheexternalreproducibilityobtainedfromthestandard

zirconGJ-1(∼0.6%and0.5–1%forthe207_Pb/206_Pb_and206_Pb/238_U,

respectively)duringindividualanalyticalsessionsandthe

within-runprecisionofeachanalysis.Analyseswithaconcordanceinthe

range90–110%wereusedforconcordiaandprobabilitydensity

distributionplots.Atotalof415analyseswerecarriedoutonfour

samples,while9%(40analyses)revealed>10%discordanceand

werediscarded.DiscordancemayoriginatefromPbloss,addition

ofcommonPborablationofdifferentdomainswithinthezircon.

Concordiadiagrams(2errorellipses),concordiaages(95%

conﬁ-dencelevel)andprobabilityplotswereproducedusingIsoplot/Ex

2.49(Ludwig,2001).The207_Pb/206_Pb_age_was_taken_for

interpre-tationforallzircons>1.0Ga,andthe206_Pb/238_U_ages_for_younger

grains.Forfurtherdetailsonanalyticalprotocolanddataprocessing

seeFreiandGerdes(2009).

3.2. Results

3.2.1. EdiacarangreywackesoftheBeirasGroup(PNC1andPNC

2)

ThezirconpopulationofsamplePNC1isdominatedby

medium-sized grains (90–120␮m; 70%) but also includes larger grains

(180–200␮m;30%).Mostzirconsaretranslucentandpinkish,and

afewarebrownandpurple.Somegrainshavemineralinclusions.

Thezirconsshowawidevarietyofformsrangingfromsubhedral

toeuhedralstubbygrainswithpyramidalormulti-pyramidal

ter-minations,subhedraltoeuhedralelongatedprismsandstrongly

roundedcrystalswithnovisiblecrystallinefaces.

Thezirconagesobtained(Fig.5andTables1and2)arequite

similarinbothsamples,withslightdifferencesforthe

percent-agesofpre-Cryogenianages(Fig.7).ForsamplePNC1,110targets

were analysed, with 110spots showing 90–110% concordance.

ThemaingroupofagesisNeoproterozoic(74%,914–550Ma).The

remainingzirconsareolder,withthefollowingdistribution:

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M.F. Pereira et al. / Precambrian Research 192– 195 (2012) 166– 189 Table1

SamplePNC1– greywacke(BeirasGroup;40◦1816N;8◦1343W).117grainsmeasured,110areconcordantintherangeof90–110%,onlyconcordantgrainsareshowninthetable.206_Pb/238_U_age_(2-error),207_Pb/206_Pb_age

(2-error),degreeofconcordance.

Number 207_Pba_(cps) _Ub_(ppm) _Pbb_(ppm) _Thb_/U 206_Pbc_/204_Pb 206_Pbc_/238_U ₂_(%) 207_Pbc_/235_U ₂_(%) 207_Pbc_/206_Pb ₂_(%) _rhod 206_Pb/238_U ₂_(Ma) 207_Pb/235_U ₂_(Ma) 207_Pb/206_Pb ₂_(Ma) _conc_(%)

a2 129,259 860 83 0.28 705 0.0942 2.1 0.776 2.4 0.0597 1.2 0.88 581 12 583 11 593 25 98 a3 40,516 351 41 0.62 2228 0.1072 2.1 0.921 2.6 0.0623 1.5 0.81 656 13 663 13 686 32 96 a4 11,240 88 10 0.54 2716 0.1049 2.0 0.901 2.8 0.0623 2.0 0.72 643 13 653 14 685 42 94 a5 3154 34 3 0.31 595 0.0911 2.8 0.747 24.9 0.0594 24.7 0.11 562 15 566 114 583 537 96 a6 17,567 184 19 0.13 2285 0.1072 2.7 0.919 3.8 0.0622 2.7 0.70 656 17 662 19 681 58 96 a7 41,106 122 30 0.68 8405 0.2186 1.9 2.476 2.1 0.0822 0.9 0.90 1274 22 1265 15 1249 18 102 a8 493,574 122 112 0.60 161,069 0.7090 2.1 29.355 3.3 0.3003 2.5 0.63 3455 56 3465 33 3472 39 100 a9 482,514 167 129 0.47 9640 0.6469 3.5 23.240 4.1 0.2606 2.1 0.86 3216 90 3237 41 3250 33 99 a10 27,466 239 28 0.82 2307 0.1035 2.0 0.883 3.6 0.0619 3.0 0.56 635 12 643 17 670 63 95 a11 18,874 135 17 0.62 2915 0.1141 2.1 0.982 6.8 0.0624 6.5 0.31 697 14 695 35 689 138 101 a13 234,265 249 107 0.43 30,629 0.3943 1.9 7.251 2.0 0.1334 0.7 0.94 2143 35 2143 18 2143 12 100 a14 161,295 155 62 0.06 64,153 0.4032 2.1 7.454 2.3 0.1341 0.9 0.91 2184 39 2168 21 2152 16 101 a15 13,680 122 13 0.57 22,761 0.0961 2.4 0.800 3.1 0.0604 2.0 0.77 591 13 597 14 617 42 96 a16 96,452 123 50 0.79 3459 0.3464 2.0 5.812 2.2 0.1217 0.9 0.91 1917 33 1948 19 1981 16 97 a17 6632 60 8 0.56 1146 0.1166 2.3 1.010 3.5 0.0628 2.6 0.66 711 16 709 18 701 56 101 a20 14,631 123 16 0.86 3017 0.1110 2.1 0.953 2.9 0.0623 2.0 0.72 679 13 680 15 683 43 99 a21 27,362 294 31 0.53 731 0.1049 2.0 0.885 3.8 0.0612 3.2 0.53 643 12 644 18 646 69 99 a22 9163 86 10 0.84 1206 0.1022 2.2 0.869 2.9 0.0616 1.9 0.75 628 13 635 14 662 41 95 a24 15,377 122 17 1.01 1870 0.1232 2.3 1.092 4.5 0.0643 3.8 0.52 749 16 750 24 752 81 100 a25 23,011 105 20 0.44 2289 0.1923 1.9 2.057 2.4 0.0776 1.4 0.80 1134 20 1135 16 1136 28 100 a26 9277 84 11 0.57 2055 0.1191 2.3 1.058 3.3 0.0644 2.4 0.69 726 16 733 18 755 51 96 a27 32,902 305 30 1.03 241 0.0927 3.3 0.751 6.1 0.0588 5.1 0.54 571 18 569 27 559 112 102 a28 16,882 114 14 0.05 10,674 0.1314 2.1 1.216 2.5 0.0671 1.4 0.82 796 16 808 14 842 30 94 a29 29,753 189 30 1.73 536 0.1306 2.7 1.186 8.2 0.0658 7.7 0.33 791 20 794 46 802 161 99 a30 23,966 188 27 0.80 926 0.1317 2.4 1.200 5.7 0.0661 5.2 0.42 797 18 801 32 810 108 98 a31 5953 59 6 0.28 6510 0.1027 2.0 0.859 3.1 0.0607 2.3 0.67 630 12 630 14 628 49 100 a32 3424 29 5 1.46 540 0.1225 3.0 1.087 6.4 0.0643 5.7 0.46 745 21 747 34 753 120 99 a33 8195 106 11 0.41 661 0.1030 2.0 0.875 4.3 0.0616 3.8 0.46 632 12 639 21 662 81 96 a36 37,395 75 29 0.87 2129 0.3329 1.9 5.574 2.3 0.1214 1.3 0.82 1852 30 1912 20 1977 23 94 a37 56,120 75 32 1.61 4007 0.3423 1.8 6.043 2.5 0.1280 1.7 0.74 1898 30 1982 22 2071 29 92 a38 3595 36 4 0.49 795 0.1108 1.9 0.944 3.8 0.0618 3.3 0.51 678 12 675 19 667 70 102 a39 1386 17 2 0.33 383 0.1242 3.2 1.086 5.6 0.0634 4.6 0.57 755 23 747 30 722 98 105 a40 15,926 157 18 0.77 2824 0.1030 1.9 0.869 4.0 0.0612 3.5 0.49 632 12 635 19 648 74 98 a41 16,089 91 12 0.54 1681 0.1275 2.6 1.144 13.7 0.0651 13.5 0.19 774 19 774 77 776 284 100 a42 42,844 42 19 1.19 7285 0.3481 2.5 6.069 2.9 0.1264 1.4 0.86 1926 41 1986 25 2049 25 94 a43 14,263 106 11 0.39 8055 0.0987 2.1 0.832 2.5 0.0611 1.3 0.85 607 12 614 12 642 29 95 a44 84,857 39 23 0.85 2821 0.4914 3.0 11.233 3.1 0.1658 1.0 0.95 2577 64 2543 30 2516 16 102 a46 1797 11 2 0.94 1620 0.1168 2.7 1.019 7.4 0.0633 6.9 0.36 712 18 713 39 718 147 99 a47 8488 44 5 0.33 2655 0.1177 2.5 1.032 4.1 0.0636 3.3 0.60 717 17 720 21 729 70 98 a48 61,322 239 34 0.07 87,210 0.1519 1.8 1.479 2.2 0.0706 1.3 0.81 912 15 922 14 946 27 96 a49 20,800 130 16 0.80 2563 0.1115 1.8 0.966 2.6 0.0628 1.9 0.70 681 12 686 13 702 40 97 a51 6032 37 5 0.62 320 0.1242 1.9 1.119 4.4 0.0653 4.0 0.44 755 14 762 24 786 84 96 a52 16,107 73 9 0.52 2504 0.1173 1.8 1.024 2.4 0.0633 1.6 0.75 715 12 716 13 719 34 99 a53 61,141 272 30 0.49 349 0.1044 2.1 0.885 4.5 0.0615 4.0 0.46 640 13 644 22 655 87 98 a54 36,466 146 13 0.04 521 0.0945 1.8 0.784 9.0 0.0601 8.8 0.20 582 10 588 41 607 191 96 a55 13,989 3 3 3.41 7574 0.5241 1.8 13.374 20.1 0.1851 20.0 0.09 2716 39 2706 210 2699 331 101 a57 20,948 6 4 1.80 1336 0.4913 2.1 11.584 2.6 0.1710 1.6 0.79 2576 44 2571 25 2568 27 100 a58 6914 22 3 0.39 8050 0.1160 1.9 1.001 3.0 0.0626 2.3 0.63 707 13 705 15 696 50 102 a59 227,567 64 34 0.63 7281 0.4673 2.2 10.949 2.7 0.1700 1.5 0.82 2472 45 2519 25 2557 26 97 a60 17,250 72 7 0.44 853 0.0909 2.2 0.737 5.1 0.0588 4.6 0.43 561 12 561 22 561 100 100 a61 38,915 20 9 1.19 4251 0.3634 2.2 5.931 2.6 0.1184 1.3 0.86 1998 38 1966 23 1932 24 103 a62 13,174 25 5 0.99 6624 0.1773 2.0 1.820 2.5 0.0744 1.5 0.81 1052 20 1053 16 1053 29 100 a63 12,784 36 5 0.80 1237 0.1233 2.7 1.111 4.7 0.0653 3.8 0.59 750 19 759 25 785 79 96 a64 13,399 10 4 0.65 2064 0.3591 2.8 5.947 4.1 0.1201 2.9 0.69 1978 48 1968 36 1958 52 101 a65 8239 18 3 2.48 526 0.1316 2.1 1.203 15.5 0.0663 15.4 0.13 797 16 802 90 816 321 98 a66 2561 7 1 1.36 642 0.1380 2.0 1.272 4.5 0.0669 4.0 0.45 833 16 833 26 834 83 100 2a-2 13,514 70 11 1.98 2798 0.1260 1.9 1.121 2.3 0.0645 1.3 0.83 765 14 763 13 759 28 101

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M.F. Pereira et al. / Precambrian Research 192– 195 (2012) 166– 189 171 Table1(Continued)

2a-3 44,507 13 11 1.29 1185 0.6398 1.7 18.852 1.8 0.2137 0.6 0.95 3188 44 3034 18 2934 10 109 2a-4 7224 42 6 1.40 1425 0.1243 1.9 1.117 3.4 0.0652 2.8 0.55 755 13 762 18 780 59 97 2a-6 11,701 80 10 0.41 2574 0.1197 2.0 1.048 2.7 0.0635 1.8 0.74 729 14 728 14 726 38 100 2a-7 13,399 94 11 0.30 8604 0.1134 1.8 0.975 2.4 0.0624 1.6 0.75 692 12 691 12 687 34 101 2a-8 9005 56 7 0.49 1406 0.1249 1.8 1.113 2.5 0.0646 1.7 0.74 759 13 760 13 762 35 100 2a-9 4853 45 6 1.80 1158 0.1117 1.8 0.993 12.1 0.0645 11.9 0.15 683 11 700 63 757 252 90 2a-10 145,541 37 31 0.65 55,306 0.6941 2.0 25.207 2.2 0.2634 0.9 0.92 3398 54 3316 22 3267 14 104 2a-11 54,493 89 31 0.22 1385 0.3471 2.8 5.664 3.1 0.1184 1.2 0.92 1921 47 1926 27 1932 22 99 2a-13 95,457 34 20 0.49 5131 0.5111 3.0 13.070 4.3 0.1855 3.0 0.71 2662 66 2685 41 2702 49 98 2a-15 10,457 58 7 0.24 2206 0.1166 2.8 1.027 6.4 0.0639 5.7 0.45 711 19 718 33 738 121 96 2a-16 14,458 75 10 0.38 1464 0.1289 2.3 1.160 4.0 0.0652 3.2 0.59 782 17 782 22 782 68 100 2a-17 42,283 13 8 0.69 6197 0.4849 3.0 12.173 3.5 0.1821 1.8 0.86 2548 64 2618 34 2672 30 95 2a-18 25,551 187 20 0.56 3809 0.1025 1.7 0.850 2.8 0.0601 2.3 0.61 629 10 625 13 608 49 103 2a-19 55,382 376 47 0.85 9382 0.1105 2.2 0.946 3.2 0.0621 2.4 0.68 676 14 676 16 677 50 100 2a-20 15,518 113 13 0.77 2039 0.1081 1.9 0.902 5.5 0.0605 5.1 0.35 662 12 653 27 622 110 106 2a-21 146,937 251 70 0.14 47,523 0.2816 2.0 4.025 2.2 0.1036 0.9 0.91 1600 28 1639 18 1690 17 95 2a-24 11,766 102 10 0.52 19,902 0.0896 1.8 0.730 2.1 0.0591 1.1 0.86 553 10 557 9 572 24 97 2a-25 7862 61 7 0.95 7481 0.1089 1.7 0.923 2.7 0.0615 2.1 0.64 666 11 664 13 655 45 102 2a-26 22,076 125 20 1.44 21,292 0.1270 1.7 1.155 1.9 0.0659 0.9 0.88 771 12 779 10 805 19 96 2a-27 6531 61 6 0.50 2762 0.0937 2.0 0.767 3.5 0.0594 2.9 0.57 578 11 578 16 580 64 100 2a-28 8133 78 7 0.52 2818 0.0910 2.0 0.739 2.8 0.0589 1.9 0.72 561 11 562 12 563 42 100 2a-29 12,968 118 12 0.63 7096 0.0965 1.9 0.796 2.9 0.0598 2.2 0.66 594 11 594 13 596 48 100 2a-30 15,967 166 19 0.48 1875 0.1119 1.7 0.961 2.6 0.0623 2.0 0.64 684 11 684 13 683 43 100 2a-31 14,254 68 11 0.50 4649 0.1523 1.9 1.461 2.4 0.0696 1.6 0.77 914 16 914 15 916 32 100 2a-32 14,010 103 13 1.03 3672 0.1080 1.8 0.920 2.5 0.0618 1.8 0.71 661 11 662 12 668 38 99 2a-33 90,219 93 43 0.84 27,187 0.4059 2.0 7.577 2.3 0.1354 1.1 0.88 2196 37 2182 21 2169 19 101 2a-35 56,372 57 24 0.49 19,813 0.3811 1.8 7.035 2.1 0.1339 1.1 0.86 2082 32 2116 19 2149 19 97 2a-36 8946 78 11 1.89 7633 0.1063 2.1 0.889 3.1 0.0607 2.3 0.67 651 13 646 15 627 50 104 2a-37 21,889 201 20 0.51 36,952 0.0961 1.9 0.786 2.3 0.0593 1.3 0.83 591 11 589 10 578 27 102 2a-38 24,200 187 26 1.20 5333 0.1056 1.9 0.911 2.4 0.0625 1.5 0.79 647 12 657 12 692 32 94 2a-39 144,968 159 55 0.20 19,526 0.3405 1.9 5.563 2.1 0.1185 0.9 0.91 1889 31 1910 18 1933 16 98 2a-40 45,555 356 33 0.46 667 0.0890 1.7 0.719 4.2 0.0586 3.9 0.40 550 9 550 18 552 85 100 2a-41 17,118 112 13 0.55 6836 0.1123 1.7 0.958 2.5 0.0619 1.9 0.67 686 11 682 13 671 40 102 2a-42 36,147 21 11 0.78 4338 0.4440 1.7 8.752 2.3 0.1430 1.6 0.71 2368 33 2312 22 2263 28 105 2a-44 3424 20 2 0.45 2250 0.1067 2.6 0.908 4.1 0.0617 3.2 0.63 654 16 656 20 664 68 98 2a-46 13,483 61 7 0.70 4308 0.1123 2.1 0.965 2.7 0.0624 1.7 0.77 686 14 686 14 686 37 100 2a-47 4261 21 3 1.03 6967 0.1087 1.8 0.917 3.3 0.0611 2.8 0.55 665 12 661 16 644 60 103 2a-48 5927 26 3 0.57 1027 0.1355 1.8 1.241 4.2 0.0664 3.8 0.42 819 14 820 24 820 79 100 2a-49 3914 14 2 1.43 6329 0.1048 2.2 0.891 3.9 0.0617 3.3 0.56 642 13 647 19 664 70 97 2a-50 11,282 41 5 0.81 17,840 0.1150 2.2 1.003 3.2 0.0632 2.2 0.71 702 15 705 16 716 47 98 2a-51 10,269 51 6 0.44 970 0.1131 2.3 0.988 8.2 0.0633 7.9 0.28 691 15 697 42 719 168 96 2a-52 9926 23 4 0.55 2177 0.1498 2.0 1.429 2.8 0.0692 1.9 0.74 900 17 901 17 905 39 99 2a-53 14,211 52 6 0.48 11,156 0.1102 2.2 0.936 3.1 0.0616 2.2 0.72 674 14 671 15 659 47 102 2a-54 101,436 58 23 0.48 5151 0.3713 2.6 6.344 2.9 0.1239 1.4 0.88 2035 45 2025 26 2014 24 101 2a-55 21,415 82 8 0.44 6112 0.0982 1.9 0.813 2.5 0.0601 1.7 0.75 604 11 604 12 605 36 100 2a-57 13,728 50 5 0.25 5336 0.1025 2.0 0.861 2.9 0.0609 2.0 0.70 629 12 631 14 635 44 99 2a-58 14,031 43 5 0.79 4111 0.1091 1.7 0.936 2.1 0.0622 1.3 0.80 667 11 671 10 681 27 98 2a-59 14,643 45 5 0.51 4101 0.1123 2.0 0.966 2.9 0.0624 2.1 0.68 686 13 687 15 688 45 100 2a-60 7446 23 2 0.53 2198 0.1035 1.9 0.878 2.6 0.0616 1.8 0.74 635 12 640 12 659 38 96 2a-61 5944 18 2 0.78 1367 0.1104 2.2 0.948 4.5 0.0623 3.9 0.50 675 14 677 22 685 83 99 2a-62 4140 6 1 0.63 5618 0.1745 2.5 1.777 5.3 0.0738 4.7 0.47 1037 24 1037 35 1037 95 100 2a-64 3139 8 1 0.97 498 0.1169 2.2 1.013 5.5 0.0628 5.0 0.40 713 15 710 28 703 107 101 2a-65 3192 9 1 0.46 415 0.1250 2.1 1.123 3.1 0.0652 2.3 0.67 759 15 765 17 780 48 97

a_Within-run_{background-corrected}_mean207_Pb_signal_in_counts_per_second.

b _U_and_Pb_content_and_Th/U_ratio_were_calculated_relative_to_GJ-1_and_are_accurate_to_{approximately}_10%.

c _Corrected_for_background,_mass_bias,_laser_induced_U–Pb_{fractionation}_and_common_Pb_(if_detectable,_see_analytical_method)_using_Stacey_and_Kramers₍₁₉₇₅₎_model_Pb_composition.207_Pb/235_U_calculated_using

207_Pb/206_Pb/(238_U/206_Pb_×_1/137.88)._Errors_are_propagated_by_quadratic_addition_of_within-run_errors_(1SE)_and_the_{reproducibility}_of_GJ-1_(1SD).

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SamplePNC2– greywacke(BeirasGroup;40◦₁₈₁₆_N;₈◦₁₃₄₃_W).₁₁₈_grains_measured,₁₀₂_are_concordant_in_the_range_of_90–110%,_only_concordant_grains_are_shown_in_the_table206_Pb/238_U_age_(2-error),207_Pb/206_Pb_age

(2-error),degreeofconcordance.

Number 207_Pba_(cps) _Ub_(ppm) _Pbb_(ppm) _Thb_U 206_Pbc_/204_Pb 206_Pbc_/238_U ₂_(%) 207_Pbc_/235_U ₂_(%) 207_Pbc_/206_Pb ₂_(%) _rhod 206_Pb/238_U ₂_(Ma) 207_Pb/235_U ₂_(Ma) 207_Pb/206_Pb ₂_(Ma) _conc_(%)

a2 26,233 164 17 0.46 477 0.0983 2.5 0.818 5.1 0.0604 4.5 0.48 604 14 607 24 617 97 98 a3 11,576 63 10 1.22 1672 0.1328 2.5 1.215 13.4 0.0663 13.2 0.19 804 19 807 78 817 276 98 a4 29,813 17 11 1.99 1114 0.4938 2.4 11.487 3.2 0.1687 2.1 0.75 2587 51 2564 30 2545 35 102 a9 11,602 73 11 0.38 15,344 0.1522 2.0 1.416 2.4 0.0675 1.3 0.84 913 17 896 14 853 27 107 a10 57,750 333 44 0.38 2535 0.1321 2.0 1.206 2.6 0.0662 1.6 0.77 800 15 803 14 813 34 98 a13 36,217 237 23 0.14 562 0.1004 1.8 0.836 3.0 0.0604 2.4 0.60 617 11 617 14 616 52 100 a14 16,029 111 13 0.54 24,823 0.1185 2.8 1.043 4.3 0.0638 3.3 0.65 722 19 726 22 736 69 98 a15 2746 12 3 2.29 917 0.1742 1.9 1.778 5.0 0.0740 4.6 0.39 1035 18 1037 33 1042 93 99 a16 25,289 33 13 0.71 1186 0.3591 2.4 6.024 2.8 0.1217 1.5 0.84 1978 40 1979 25 1981 27 100 a17 15,591 140 13 0.38 2385 0.0937 2.5 0.769 13.9 0.0595 13.7 0.18 578 14 579 63 584 297 99 a18 12,511 95 16 0.68 261 0.1663 2.0 1.688 2.4 0.0736 1.3 0.84 992 19 1004 15 1030 26 96 a19 10,266 73 10 0.45 1167 0.1301 2.3 1.182 3.1 0.0659 2.1 0.74 788 17 792 17 804 43 98 a20 14,724 84 10 0.35 1398 0.1169 2.8 1.021 6.2 0.0634 5.5 0.45 713 19 715 32 721 118 99 a21 14,724 84 10 0.34 1618 0.1220 2.6 1.092 5.8 0.0649 5.2 0.44 742 18 750 31 771 109 96 a22 14,144 56 10 0.70 373 0.1583 2.9 1.578 12.3 0.0723 11.9 0.24 947 26 962 79 994 243 95 a24 8816 72 9 0.65 1949 0.1110 2.5 0.950 3.8 0.0621 2.9 0.65 679 16 678 19 676 62 100 a25 13,046 45 10 0.64 979 0.1883 2.4 2.004 5.8 0.0772 5.3 0.41 1112 24 1117 40 1126 105 99 a26 24,083 169 24 1.13 1804 0.1226 2.1 1.089 3.0 0.0644 2.1 0.70 746 15 748 16 754 45 99 a27 42,844 328 40 0.52 623 0.1174 2.3 1.038 3.5 0.0641 2.7 0.65 716 15 723 18 744 56 96 a28 39,513 73 27 0.72 329 0.3146 3.3 4.562 4.8 0.1052 3.5 0.68 1763 50 1742 41 1718 65 103 a29 10,854 46 17 0.28 358 0.3599 2.0 4.760 15.3 0.0959 15.2 0.13 1982 33 1778 138 1546 286 128 a30 47,610 170 32 0.19 765 0.1795 1.9 1.899 6.5 0.0767 6.2 0.30 1064 19 1081 44 1114 123 96 a31 1611 13 2 2.54 2581 0.1102 3.0 0.938 6.9 0.0617 6.2 0.44 674 19 672 34 664 132 102 a32 74,621 58 28 0.42 41 0.3173 3.7 5.068 23.5 0.1159 23.3 0.16 1776 58 1831 222 1893 418 94 a35 8440 40 9 1.32 1014 0.1911 2.0 2.038 6.8 0.0773 6.5 0.30 1128 21 1128 47 1129 129 100 a36 6415 53 9 0.80 460 0.1655 2.0 1.646 3.1 0.0722 2.5 0.62 987 18 988 20 990 50 100 a37 20,341 129 18 0.67 1817 0.1329 2.2 1.221 3.3 0.0666 2.4 0.67 804 17 810 18 827 51 97 a38 3958 53 7 0.87 356 0.1295 1.9 1.172 8.6 0.0656 8.4 0.22 785 14 788 48 795 176 99 a39 21,619 101 14 0.57 264 0.1240 2.1 1.105 7.4 0.0646 7.1 0.28 754 15 756 40 762 149 99 a40 24,344 80 12 0.57 253 0.1288 2.4 1.159 11.8 0.0653 11.6 0.20 781 18 781 66 782 243 100 a43 12,243 51 10 0.71 2218 0.1956 1.9 2.126 3.3 0.0788 2.7 0.58 1152 20 1157 23 1167 53 99 a44 93,499 48 25 0.33 483 0.4659 2.4 10.601 2.7 0.1650 1.3 0.88 2466 49 2489 26 2508 22 98 a46 31,889 14 7 1.04 45 0.3148 2.4 4.545 24.3 0.1047 24.2 0.10 1764 37 1739 225 1709 445 103 a48 6287 38 6 0.42 276 0.1548 2.3 1.575 8.5 0.0738 8.2 0.27 928 20 960 54 1036 166 90 a49 4402 8 2 1.03 242 0.1696 2.1 1.747 16.5 0.0747 16.4 0.13 1010 20 1026 113 1060 329 95 a50 67,607 43 19 0.85 2228 0.3633 3.9 6.377 4.4 0.1273 2.1 0.88 1998 67 2029 39 2061 37 97 a51 44,850 96 15 0.46 167 0.1292 2.7 1.208 9.8 0.0678 9.4 0.28 783 20 804 56 863 195 91 a52 36,472 185 20 0.44 3551 0.1077 2.0 0.913 2.8 0.0615 2.0 0.72 659 13 659 14 656 42 100 a53 29,700 115 16 0.67 1086 0.1303 1.9 1.195 3.6 0.0665 3.1 0.51 790 14 798 20 822 65 96 a54 34,013 121 17 0.75 818 0.1365 2.0 1.228 3.1 0.0653 2.4 0.64 825 16 813 18 783 50 105 a57 45,734 23 11 0.61 1382 0.4276 2.0 8.295 2.5 0.1407 1.5 0.80 2295 39 2264 23 2236 26 103 a58 53,971 68 12 0.09 488 0.1566 2.0 1.521 13.0 0.0704 12.9 0.15 938 17 939 83 941 264 100 a59 37,698 33 7 0.51 84 0.1401 1.8 1.254 9.4 0.0649 9.2 0.20 845 15 825 54 771 193 110 a60 3253 13 2 0.13 485 0.1236 2.9 1.100 4.2 0.0645 3.1 0.68 751 20 753 23 759 65 99 a61 3451 12 2 1.92 527 0.1300 2.3 1.153 4.6 0.0643 4.0 0.51 788 17 778 25 752 84 105 a63 42,808 14 8 0.40 1604 0.5276 3.3 12.546 3.5 0.1725 1.3 0.93 2731 73 2646 33 2582 21 106 a65 14,094 27 4 0.83 584 0.1344 3.1 1.243 7.7 0.0671 7.1 0.40 813 23 820 44 840 147 97 a66 2826 7 1 1.11 227 0.1326 2.7 1.209 14.0 0.0661 13.7 0.19 803 21 805 81 811 287 99 2a-2 20,373 84 11 0.45 277 0.1209 3.4 1.098 10.9 0.0659 10.3 0.31 736 24 752 59 803 216 92 2a-4 2697 21 3 1.60 4448 0.1040 3.2 0.870 5.9 0.0607 5.0 0.53 638 19 636 28 628 108 102 2a-5 15,211 104 16 1.88 1381 0.1174 2.2 1.013 3.7 0.0626 2.9 0.61 715 15 711 19 696 62 103 2a-6 7553 59 7 1.34 679 0.0989 2.3 0.842 3.6 0.0618 2.7 0.64 608 13 620 17 666 59 91 2a-7 13,898 14 7 1.81 2338 0.4039 2.4 6.906 3.0 0.1240 1.8 0.79 2187 44 2099 27 2015 33 109

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Number 207_Pba_(cps) _Ub_(ppm) _Pbb_(ppm) _Thb_U 206_Pbc_/204_Pb 206_Pbc_/238_U ₂_(%) 207_Pbc_/235_U ₂_(%) 207_Pbc_/206_Pb ₂_(%) _rhod 206_Pb/238_U ₂_(Ma) 207_Pb/235_U ₂_(Ma) 207_Pb/206_Pb ₂_(Ma) _conc_(%)

2a-8 10,803 84 9 0.36 3799 0.1097 2.6 0.954 9.4 0.0631 9.0 0.28 671 17 680 48 712 191 94 2a-9 20,450 185 16 0.14 6326 0.0912 2.3 0.747 2.7 0.0594 1.5 0.83 563 12 567 12 582 33 97 2a-10 39,461 322 34 0.63 1898 0.0991 2.4 0.839 2.8 0.0615 1.3 0.88 609 14 619 13 655 28 93 2a-11 14,641 101 12 0.89 1353 0.1023 2.1 0.858 5.0 0.0608 4.6 0.43 628 13 629 24 632 98 99 2a-13 60,766 74 31 0.96 18,723 0.3551 2.2 5.741 2.5 0.1173 1.1 0.90 1959 38 1938 22 1915 20 102 2a-14 43,978 358 37 0.44 2248 0.1000 2.4 0.834 2.8 0.0605 1.4 0.86 614 14 616 13 622 30 99 2a-15 31,027 240 28 0.73 29,135 0.1062 2.3 0.894 2.7 0.0611 1.6 0.82 650 14 649 13 643 34 101 2a-16 16,946 105 14 0.70 2261 0.1275 2.3 1.165 3.5 0.0662 2.6 0.65 774 16 784 19 814 55 95 2a-17 24,525 153 20 0.58 1659 0.1198 2.3 1.028 4.9 0.0622 4.3 0.47 729 16 718 25 682 92 107 2a-18 14,260 120 13 0.54 7441 0.1004 2.4 0.833 3.2 0.0601 2.0 0.77 617 14 615 15 609 44 101 2a-19 17,658 124 14 0.76 7466 0.1027 2.7 0.890 3.4 0.0629 1.9 0.82 630 16 646 16 704 41 90 2a-20 31,090 290 31 0.93 3616 0.0949 2.1 0.771 3.1 0.0589 2.2 0.69 584 12 580 14 565 49 103 2a-21 42,256 280 34 0.44 2170 0.1167 2.7 0.993 3.4 0.0617 2.1 0.78 712 18 700 18 665 46 107 2a-22 30,424 248 27 0.52 6326 0.1057 2.4 0.891 2.8 0.0611 1.5 0.86 648 15 647 14 644 31 101 2a-24 10,705 70 8 1.22 901 0.0952 3.5 0.792 8.3 0.0603 7.5 0.42 586 20 592 38 616 163 95 2a-25 18,340 112 17 1.17 2239 0.1317 2.6 1.209 3.1 0.0666 1.8 0.82 798 19 805 18 825 37 97 2a-26 24,690 214 23 0.72 18,373 0.0983 2.4 0.810 2.8 0.0598 1.4 0.87 605 14 603 13 595 29 102 2a-27 18,189 173 18 0.41 1067 0.1062 2.6 0.894 4.5 0.0611 3.6 0.59 650 16 649 22 643 78 101 2a-28 41,209 306 34 0.65 1148 0.1029 2.6 0.855 4.2 0.0603 3.2 0.63 631 16 627 20 614 70 103 2a-29 29,098 179 25 1.13 865 0.1160 2.7 1.022 4.1 0.0639 3.0 0.67 707 18 715 21 738 64 96 2a-30 11,807 90 15 2.38 18,828 0.1186 2.4 1.032 3.5 0.0631 2.4 0.71 723 17 720 18 711 52 102 2a-31 17,960 20 9 1.09 1973 0.3850 2.5 6.373 3.2 0.1201 2.0 0.78 2100 44 2029 28 1957 35 107 2a-33 3569 28 4 0.62 725 0.1202 2.6 1.068 4.6 0.0644 3.8 0.57 732 18 738 24 756 79 97 2a-35 54,493 338 42 1.22 478 0.1033 3.6 0.852 4.4 0.0598 2.6 0.82 634 22 626 21 597 55 106 2a-36 60,582 70 31 0.81 1030 0.3779 2.4 6.202 2.8 0.1190 1.4 0.86 2066 43 2005 25 1942 26 106 2a-38 13,732 117 12 0.59 4489 0.0983 2.5 0.823 2.9 0.0607 1.4 0.87 605 15 610 13 628 31 96 2a-39 13,078 95 10 0.28 4377 0.1141 2.4 0.962 3.1 0.0611 2.0 0.77 697 16 684 16 643 43 108 2a-40 38,319 204 27 1.06 1071 0.1093 2.8 0.936 4.6 0.0621 3.6 0.61 669 18 671 23 677 77 99 2a-41 220,472 52 44 0.64 6151 0.7178 2.1 27.511 2.1 0.2780 0.3 0.99 3488 57 3402 21 3352 5 104 2a-42 21,959 158 23 1.12 794 0.1333 2.6 1.193 4.2 0.0650 3.4 0.61 806 20 798 24 773 71 104 2a-43 12,561 73 7 0.26 7834 0.0948 4.4 0.787 5.8 0.0602 3.8 0.76 584 25 590 26 612 82 95 2a-44 4223 22 3 2.05 884 0.1113 2.5 0.979 4.0 0.0638 3.1 0.63 680 16 693 20 735 66 93 2a-46 102,619 38 25 0.80 15,122 0.5598 2.4 13.966 2.6 0.1809 1.1 0.91 2866 56 2747 25 2662 18 108 2a-47 44,839 155 22 0.44 7473 0.1369 2.6 1.260 2.9 0.0667 1.2 0.91 827 21 828 17 829 26 100 2a-48 20,656 55 10 1.13 1615 0.1742 2.5 1.783 3.7 0.0742 2.8 0.66 1035 24 1039 25 1047 57 99 2a-49 20,981 92 13 2.23 3363 0.1069 2.4 0.921 3.8 0.0625 3.0 0.63 655 15 663 19 691 63 95 2a-50 12,577 38 5 0.94 1593 0.1281 2.4 1.190 8.4 0.0673 8.0 0.29 777 18 796 47 849 167 92 2a-51 21,473 64 9 0.87 3029 0.1304 2.6 1.214 3.8 0.0675 2.8 0.67 790 19 807 21 853 59 93 2a-52 26,640 89 11 0.98 1307 0.1073 2.2 0.922 4.1 0.0623 3.5 0.53 657 14 663 20 684 75 96 2a-53 47,974 126 18 0.69 4889 0.1348 2.3 1.220 2.7 0.0656 1.3 0.87 815 18 810 15 795 27 103 2a-55 24,130 31 7 1.61 160 0.1561 2.5 1.530 7.5 0.0711 7.1 0.33 935 22 943 47 961 145 97 2a-58 31,473 101 10 0.59 41,683 0.0925 2.2 0.752 3.0 0.0589 2.1 0.73 570 12 569 13 564 46 101 2a-60 25,000 92 9 0.54 5666 0.0952 2.3 0.784 2.9 0.0598 1.7 0.81 586 13 588 13 596 36 98 2a-61 10,750 34 4 0.49 2030 0.1071 2.4 0.934 3.8 0.0633 2.9 0.64 656 15 670 19 717 62 91 2a-62 17,958 48 5 0.45 6055 0.1116 2.4 0.946 2.9 0.0615 1.5 0.85 682 16 676 14 655 32 104 2a-63 17,117 55 5 0.40 5620 0.0946 2.3 0.781 2.7 0.0599 1.5 0.83 582 13 586 12 599 33 97 2a-64 15,558 50 6 0.53 1072 0.1107 2.4 0.973 3.9 0.0638 3.1 0.61 677 15 690 20 734 66 92 2a-65 47,431 99 14 0.09 10,231 0.1435 2.4 1.304 3.8 0.0659 2.9 0.63 865 19 847 22 803 61 108 2a-66 29,840 73 9 0.89 2641 0.1056 2.7 0.879 4.1 0.0604 3.1 0.66 647 17 641 20 618 67 105

(9)

SamplePNC3– arkosicquartzite(SarnelhasFormation;40◦1715N;8◦1538W).120grainsmeasured,113areconcordantintherangeof90–110%,onlyconcordantgrainsareshowninthetable.206_Pb/238_U_age_(2-error),

207_Pb/206_Pb_age_(2-error),_degree_of_concordance.

a3 27,402 80 10 0.46 243 0.1127 2.5 0.966 11.3 0.0621 11.0 0.22 689 16 686 58 679 235 101 a4 125,510 102 46 1.37 14,623 0.3713 1.5 6.061 1.6 0.1184 0.6 0.93 2035 27 1985 14 1932 11 105 a5 7572 42 5 0.56 1591 0.1077 1.6 0.917 2.5 0.0618 2.0 0.62 659 10 661 12 666 43 99 a6 21,381 111 13 0.65 6806 0.1089 1.7 0.938 2.3 0.0625 1.6 0.72 666 11 672 11 691 34 96 a7 20,333 93 12 0.54 17,022 0.1228 2.1 1.064 2.8 0.0629 1.9 0.73 747 15 736 15 704 41 106 a8 27,163 209 25 0.95 1059 0.0793 1.5 0.619 4.8 0.0566 4.6 0.32 492 7 489 19 478 101 103 a9 8865 63 6 0.68 1354 0.0876 1.7 0.709 2.4 0.0587 1.6 0.73 541 9 544 10 556 35 97 a10 12,143 78 10 1.48 19,318 0.0994 1.6 0.828 2.0 0.0604 1.2 0.79 611 9 612 9 618 26 99 a13 9696 58 6 0.86 1602 0.0987 1.8 0.824 2.6 0.0605 1.9 0.70 607 10 610 12 623 40 97 a14 2720 17 2 0.40 987 0.0985 1.8 0.826 4.1 0.0608 3.7 0.45 606 11 611 19 632 79 96 a15 5182 28 4 1.46 1556 0.1128 1.5 0.963 3.7 0.0619 3.4 0.40 689 10 685 19 671 73 103 a16 22,567 120 13 0.88 36,575 0.0940 1.6 0.768 1.9 0.0593 1.2 0.80 579 9 579 9 578 25 100 a17 39,532 269 26 0.55 3295 0.0935 1.7 0.763 2.3 0.0592 1.6 0.73 576 9 576 10 576 34 100 a18 40,310 299 26 0.49 2623 0.0861 1.5 0.692 2.1 0.0583 1.5 0.71 532 8 534 9 541 32 98 a19 42,654 295 28 0.47 8457 0.0925 1.5 0.736 2.2 0.0578 1.6 0.70 570 8 560 10 521 35 109 a20 8565 61 6 0.88 3143 0.0906 1.5 0.727 2.4 0.0582 1.9 0.60 559 8 555 10 539 42 104 a21 15,623 126 12 0.17 565 0.0972 2.0 0.827 3.9 0.0617 3.3 0.51 598 11 612 18 665 71 90 a22 134,033 65 37 0.85 9096 0.4723 1.5 11.010 2.0 0.1691 1.4 0.73 2494 30 2524 19 2548 23 98 a24 46,536 349 38 1.20 3300 0.0932 2.2 0.755 2.4 0.0588 0.9 0.92 574 12 571 10 559 21 103 a25 10,826 88 7 0.58 18,086 0.0823 1.3 0.653 3.0 0.0575 2.7 0.44 510 7 510 12 510 59 100 a26 29,680 219 26 1.34 48,241 0.0991 1.5 0.808 2.0 0.0592 1.4 0.71 609 8 601 9 573 31 106 a27 9759 106 8 0.20 780 0.0808 1.7 0.632 3.3 0.0567 2.8 0.51 501 8 498 13 482 62 104 a28 9388 81 9 2.40 6518 0.0787 2.0 0.619 2.9 0.0570 2.0 0.71 489 10 489 11 493 45 99 a29 27,736 220 20 0.51 20,183 0.0863 1.7 0.693 2.5 0.0582 1.9 0.67 534 9 535 11 538 41 99 a30 37,727 378 31 0.35 18,820 0.0828 1.5 0.654 1.6 0.0573 0.7 0.91 513 7 511 7 505 15 102 a31 36,877 321 29 0.43 7259 0.0877 1.6 0.709 2.7 0.0586 2.2 0.59 542 8 544 11 552 47 98 a33 18,072 144 16 1.24 16,321 0.0946 1.7 0.768 2.2 0.0589 1.3 0.80 583 10 579 10 564 28 103 a35 154,060 212 75 0.69 46,951 0.3217 1.7 4.966 1.9 0.1119 0.8 0.90 1798 27 1813 16 1831 15 98 a36 15,515 125 15 1.48 7770 0.0946 1.9 0.763 2.7 0.0585 2.0 0.68 583 10 576 12 549 43 106 a37 129,056 72 40 0.85 14,323 0.4761 1.8 11.134 2.0 0.1696 0.8 0.92 2510 37 2534 18 2554 13 98 a38 8301 48 6 1.00 12,516 0.1210 1.6 1.064 2.5 0.0638 2.0 0.61 736 11 736 13 734 42 100 a39 46,477 57 22 1.23 43,321 0.3109 1.7 4.417 2.2 0.1030 1.4 0.76 1745 25 1716 18 1680 26 104 a40 12,345 87 8 0.33 3182 0.0880 1.5 0.711 2.5 0.0586 1.9 0.62 544 8 545 11 551 42 99 a41 15,830 105 11 1.02 25,276 0.0937 1.9 0.778 3.5 0.0602 2.9 0.55 577 10 584 16 611 63 95 a42 18,350 122 10 0.39 4373 0.0845 1.6 0.674 2.7 0.0578 2.1 0.62 523 8 523 11 523 46 100 a43 15,567 16 9 3.60 2930 0.3089 2.3 4.601 3.2 0.1080 2.3 0.71 1735 35 1750 27 1767 41 98 a44 3293 16 2 0.83 781 0.1062 2.3 0.882 4.9 0.0602 4.3 0.47 651 14 642 24 612 93 106 a46 3771 19 2 0.05 800 0.1111 1.7 0.955 5.2 0.0623 4.9 0.33 679 11 681 26 686 105 99 a47 18,749 86 10 1.11 6935 0.1035 1.5 0.859 2.1 0.0602 1.4 0.73 635 9 630 10 612 31 104 a48 7125 32 3 0.69 11,513 0.0983 2.1 0.804 3.5 0.0593 2.8 0.59 604 12 599 16 578 61 104 a49 88,981 30 17 0.53 10,999 0.5078 1.8 11.732 2.6 0.1676 1.9 0.69 2647 39 2583 24 2534 31 104 a50 24,791 144 12 0.71 2728 0.0784 2.0 0.622 3.3 0.0575 2.6 0.61 486 9 491 13 512 58 95 a51 8331 38 4 0.85 10,312 0.0907 1.7 0.747 2.5 0.0598 1.8 0.70 560 9 567 11 595 39 94 a52 8160 34 3 0.42 6656 0.0954 1.5 0.771 2.8 0.0586 2.4 0.54 587 9 580 13 554 52 106 a53 9135 43 3 0.25 1678 0.0810 1.6 0.647 2.3 0.0579 1.6 0.71 502 8 506 9 527 35 95 a54 12,233 57 5 0.40 20,159 0.0903 1.8 0.725 2.4 0.0582 1.6 0.74 557 9 554 10 539 35 103 a55 6383 27 2 0.48 1470 0.0844 1.8 0.672 3.4 0.0578 3.0 0.51 522 9 522 14 522 65 100 a57 6861 31 3 0.47 1512 0.0867 1.5 0.694 2.7 0.0581 2.2 0.56 536 8 535 11 533 49 101 a58 52,649 20 10 0.87 26,291 0.4018 1.9 7.205 2.3 0.1300 1.4 0.80 2177 35 2137 21 2099 24 104 a59 45,090 17 8 0.74 4860 0.3902 2.2 7.192 2.6 0.1337 1.4 0.85 2124 40 2136 23 2147 24 99 a60 87,247 38 15 0.85 5487 0.3614 4.1 5.777 4.2 0.1159 1.2 0.96 1989 70 1943 37 1895 21 105 a61 10,893 48 4 0.24 17,173 0.0780 3.2 0.612 4.0 0.0569 2.4 0.80 484 15 485 15 488 52 99 a62 21,808 64 6 0.39 35,607 0.0999 1.6 0.811 2.1 0.0588 1.4 0.75 614 9 603 10 561 30 109 a63 17,243 57 6 0.46 12,828 0.0951 1.7 0.768 2.1 0.0586 1.3 0.80 585 9 578 9 551 28 106 a64 13,769 31 3 0.57 720 0.0895 1.9 0.740 6.6 0.0599 6.3 0.29 553 10 562 29 600 136 92 a65 38,131 9 5 1.30 5508 0.4572 1.7 9.779 2.2 0.1551 1.4 0.77 2427 34 2414 20 2403 23 101 a66 10,167 35 3 0.37 16,551 0.0944 1.5 0.769 2.0 0.0590 1.3 0.74 582 8 579 9 569 29 102

(10)

2a-2 94,760 111 40 0.25 14,458 0.3487 1.7 6.103 2.1 0.1270 1.2 0.81 1928 29 1991 19 2056 22 94 2a-3 41,944 24 17 2.15 2826 0.4779 1.5 12.009 2.1 0.1822 1.5 0.72 2518 32 2605 20 2673 25 94 2a-4 154,031 86 48 0.77 9376 0.4685 1.3 11.579 1.8 0.1793 1.2 0.75 2477 28 2571 17 2646 20 94 2a-5 5540 41 5 1.13 9124 0.1070 1.7 0.891 3.2 0.0604 2.8 0.51 655 10 647 16 617 60 106 2a-6 40,334 385 39 0.55 8110 0.0956 1.0 0.809 1.9 0.0613 1.6 0.56 589 6 602 9 651 33 90 2a-7 22,653 204 16 0.24 2483 0.0822 1.5 0.654 3.1 0.0577 2.7 0.47 509 7 511 13 517 60 99 2a-9 33,436 231 24 0.36 2601 0.0991 1.2 0.806 3.0 0.0590 2.8 0.39 609 7 600 14 567 61 107 2a-10 167,180 77 48 0.61 83,472 0.5295 1.6 14.568 2.2 0.1995 1.5 0.73 2739 35 2787 21 2822 24 97 2a-11 29,927 331 27 0.48 23,731 0.0789 0.9 0.619 1.4 0.0569 1.1 0.64 490 4 489 6 489 24 100 2a-13 3991 33 4 1.23 4853 0.1031 1.8 0.870 3.5 0.0612 3.0 0.51 633 11 636 17 646 64 98 2a-14 14,409 126 12 0.36 2940 0.0939 1.2 0.757 5.2 0.0585 5.0 0.24 578 7 573 23 549 109 105 2a-15 21,139 44 11 1.49 233 0.1693 1.3 1.771 8.4 0.0759 8.3 0.15 1008 12 1035 56 1092 167 92 2a-16 18,024 163 16 0.40 29,941 0.0986 1.2 0.813 1.9 0.0598 1.5 0.62 606 7 604 9 597 32 102 2a-17 35,310 289 38 1.23 10,184 0.1080 1.1 0.910 1.7 0.0611 1.3 0.62 661 7 657 8 643 29 103 2a-18 28,145 247 24 0.24 15,719 0.1022 1.1 0.857 1.8 0.0608 1.4 0.60 627 6 628 8 632 31 99 2a-19 27,934 197 21 0.45 20,288 0.1040 2.0 0.889 2.7 0.0620 1.9 0.72 638 12 646 13 675 40 95 2a-20 22,061 196 22 0.66 35,940 0.1050 1.0 0.882 2.2 0.0609 2.0 0.44 644 6 642 11 637 42 101 2a-21 158,960 165 68 0.32 91,201 0.3915 1.5 6.918 1.8 0.1282 1.0 0.84 2130 28 2101 16 2073 18 103 2a-22 23,555 222 21 0.44 39,634 0.0929 1.1 0.758 1.7 0.0592 1.3 0.65 573 6 573 7 573 28 100 2a-24 26,969 308 33 1.06 20,339 0.0798 1.2 0.635 1.6 0.0577 1.1 0.72 495 6 499 6 520 25 95 2a-25 9387 86 9 0.41 10,034 0.0968 1.1 0.798 2.2 0.0598 1.9 0.51 596 6 596 10 596 42 100 2a-26 21,283 237 23 0.50 2159 0.0940 1.0 0.775 1.8 0.0598 1.5 0.54 579 5 582 8 595 33 97 2a-27 23,127 220 21 0.32 29,947 0.0976 1.4 0.811 1.8 0.0603 1.1 0.79 600 8 603 8 614 23 98 2a-28 154,291 155 70 0.61 52,052 0.4112 1.3 7.627 1.7 0.1345 1.1 0.78 2220 25 2188 15 2158 19 103 2a-29 16,333 150 14 0.17 8855 0.0960 1.0 0.789 2.1 0.0596 1.8 0.49 591 6 591 9 590 40 100 2a-30 12,429 137 15 0.85 3906 0.0971 1.5 0.798 2.5 0.0596 2.0 0.61 598 9 596 11 589 43 101 2a-31 5740 27 5 1.07 7401 0.1512 1.7 1.473 3.0 0.0707 2.5 0.56 908 14 919 18 948 51 96 2a-32 22,055 234 21 0.36 7778 0.0894 0.9 0.724 1.8 0.0587 1.5 0.53 552 5 553 8 557 33 99 2a-33 14,161 94 12 0.93 3643 0.1140 2.0 0.990 5.5 0.0630 5.2 0.35 696 13 699 28 708 110 98 2a-35 1774 19 2 0.43 2903 0.0981 1.4 0.832 6.4 0.0615 6.2 0.23 603 8 615 30 657 133 92 2a-36 3720 29 4 1.43 2191 0.1192 1.9 1.033 4.1 0.0628 3.7 0.46 726 13 720 22 702 78 103 2a-37 27,709 182 24 0.34 43,086 0.1318 1.3 1.165 2.0 0.0641 1.5 0.64 798 10 784 11 745 33 107 2a-38 9566 87 8 0.34 16,226 0.0971 1.1 0.785 2.5 0.0586 2.3 0.43 597 6 588 11 553 50 108 2a-39 18,269 135 16 0.82 18,111 0.1085 1.4 0.916 2.1 0.0612 1.6 0.66 664 9 660 10 647 34 103 2a-40 6019 46 6 0.80 824 0.1215 1.5 1.094 2.7 0.0653 2.2 0.55 739 10 750 14 784 47 94 2a-41 5309 33 4 0.48 8537 0.1075 2.6 0.916 3.9 0.0618 2.9 0.67 658 16 660 19 667 62 99 2a-42 13,720 86 10 0.63 12,157 0.1076 1.2 0.915 2.1 0.0616 1.8 0.55 659 7 660 10 661 38 100 2a-43 114,694 149 56 1.30 524 0.3026 2.9 4.648 3.2 0.1114 1.4 0.90 1704 44 1758 27 1823 26 94 2a-44 68,730 79 28 1.00 3313 0.3012 1.3 4.816 1.5 0.1159 0.8 0.86 1697 19 1788 13 1895 14 90 2a-46 247,560 181 72 0.38 138,853 0.3784 1.7 6.533 2.0 0.1252 1.1 0.85 2069 31 2050 18 2032 19 102 2a-47 13,530 79 8 0.39 22,958 0.0969 1.2 0.783 2.5 0.0586 2.2 0.48 596 7 587 11 551 49 108 2a-48 16,179 67 9 0.83 24,591 0.1239 1.6 1.112 2.8 0.0651 2.4 0.55 753 11 759 15 776 50 97 2a-49 6205 31 4 0.75 5171 0.1040 1.6 0.853 3.2 0.0595 2.8 0.48 638 9 626 15 585 61 109 2a-50 45,009 201 24 0.74 73,911 0.1097 1.3 0.917 1.8 0.0606 1.2 0.73 671 8 661 9 625 27 107 2a-51 25,355 121 12 0.45 11,790 0.0975 1.0 0.804 1.8 0.0598 1.5 0.58 600 6 599 8 597 32 101 2a-52 39,320 173 18 0.43 62,175 0.0996 1.3 0.847 2.1 0.0617 1.6 0.62 612 7 623 10 663 35 92 2a-53 12,232 46 5 0.34 19,528 0.1114 1.4 0.955 2.5 0.0622 2.0 0.58 681 9 681 12 680 43 100 2a-54 10,568 42 5 1.10 3669 0.1042 1.5 0.862 2.7 0.0600 2.3 0.54 639 9 631 13 604 49 106 2a-57 188,894 90 38 0.50 38,939 0.3900 1.6 6.743 1.8 0.1254 0.9 0.87 2123 29 2078 16 2035 16 104 2a-58 29,607 17 7 1.53 1300 0.3302 1.7 5.424 2.5 0.1192 1.8 0.70 1839 28 1889 21 1944 32 95 2a-59 67,619 36 14 0.63 57,912 0.3528 1.3 5.652 1.8 0.1162 1.2 0.72 1948 21 1924 15 1899 22 103 2a-60 255,719 181 64 0.54 16,348 0.3327 1.6 5.629 4.8 0.1227 4.5 0.34 1851 26 1921 42 1996 80 93 2a-61 77,781 32 14 0.74 19,395 0.3932 1.6 7.009 1.9 0.1293 1.0 0.85 2138 29 2113 17 2088 17 102 2a-62 10,777 38 4 0.58 18,195 0.0927 1.3 0.752 2.5 0.0589 2.1 0.54 572 7 570 11 562 45 102 2a-64 21,623 80 7 0.66 9279 0.0773 20.0 0.610 20.1 0.0572 1.7 1.00 480 93 483 80 499 37 96 2a-66 17,198 50 5 0.64 28,548 0.0977 1.1 0.808 1.7 0.0599 1.2 0.67 601 6 601 8 601 27 100

(11)

SamplePNC4–quartzite(ArmoricanQuartziteFormation–Penacova;40◦₁₇₀₃_N;₈◦₁₅₅₀_W).₆₀_grains_measured,₅₀_are_concordant_in_the_range_of_90–110%,_only_concordant_grains_are_shown_in_the_table.206_Pb/238_U_age

(2-error),207_Pb/206_Pb_age_(2-error),_degree_of_concordance.

a2 13,357 76 11 0.64 7763 0.1360 2.6 1.227 2.9 0.0655 1.3 0.90 822 20 813 16 789 27 104 a3 5810 32 4 1.11 1533 0.1190 2.5 1.033 4.5 0.0629 3.7 0.57 725 17 720 23 706 78 103 a5 9844 56 8 0.59 1180 0.1435 2.8 1.372 5.4 0.0693 4.6 0.51 865 22 877 32 909 95 95 a7 6751 62 6 0.30 3855 0.0937 2.3 0.771 3.3 0.0597 2.3 0.71 577 13 580 15 591 51 98 a9 15,264 42 8 1.35 4984 0.1650 2.2 1.637 2.8 0.0719 1.8 0.78 985 20 985 18 984 36 100 a10 15,885 80 8 0.16 360 0.0959 2.5 0.779 6.1 0.0590 5.6 0.40 590 14 585 28 566 122 104 a11 17,896 105 12 0.48 3234 0.1162 2.6 1.012 3.7 0.0632 2.6 0.71 708 17 710 19 714 55 99 a13 11,816 48 8 1.89 334 0.1291 2.1 1.207 5.4 0.0678 4.9 0.39 783 16 804 30 863 102 91 a14 11,486 105 11 1.23 3005 0.0961 2.5 0.775 3.2 0.0585 2.0 0.78 592 14 583 14 548 44 108 a15 9020 71 8 0.43 3563 0.1048 2.7 0.881 3.7 0.0610 2.5 0.74 642 16 642 18 639 53 100 a16 86,694 149 37 0.22 10,539 0.2513 2.4 3.199 2.8 0.0923 1.3 0.88 1445 32 1457 22 1474 26 98 a17 39,696 238 31 0.63 800 0.1212 2.8 1.049 4.1 0.0628 2.9 0.70 738 20 728 21 700 62 105 a18 14,924 116 13 0.42 2540 0.1106 2.2 0.930 3.4 0.0610 2.6 0.65 676 14 668 17 639 55 106 a19 11,002 61 10 1.62 1609 0.1253 2.5 1.122 4.0 0.0650 3.1 0.62 761 18 764 22 773 66 98 a21 11,437 54 9 0.84 16,662 0.1468 2.4 1.383 3.4 0.0683 2.5 0.70 883 20 882 21 878 51 101 a22 9454 45 7 0.62 4779 0.1554 2.6 1.484 3.5 0.0693 2.4 0.73 931 22 924 21 906 49 103 a24 12,394 69 9 1.10 465 0.1042 2.3 0.861 8.1 0.0599 7.8 0.29 639 14 631 39 600 169 106 a25 20,575 32 13 2.29 451 0.3259 3.8 5.504 5.2 0.1225 3.6 0.73 1819 61 1901 46 1992 63 91 a28 22,121 248 24 1.06 1660 0.0872 2.7 0.694 4.7 0.0577 3.9 0.57 539 14 535 20 520 85 104 a29 13,325 89 10 0.41 2992 0.1097 3.1 0.951 3.5 0.0629 1.5 0.90 671 20 679 17 704 32 95 a30 17,270 155 17 0.41 14,367 0.1067 2.7 0.889 4.4 0.0605 3.5 0.61 653 17 646 21 620 75 105 a33 15,396 177 15 0.48 15,101 0.0816 2.4 0.657 3.5 0.0585 2.6 0.68 505 12 513 14 547 56 92 a35 26,514 257 25 0.43 7368 0.0970 2.5 0.826 3.1 0.0617 1.8 0.82 597 15 611 14 665 38 90 a36 7223 43 6 0.55 10,615 0.1347 3.0 1.279 5.4 0.0689 4.5 0.55 815 23 836 31 895 94 91 a37 13,380 106 12 0.79 21,228 0.1022 2.5 0.882 3.3 0.0626 2.1 0.77 627 15 642 16 695 45 90 a38 10,288 85 9 0.29 4421 0.1050 2.5 0.870 3.3 0.0601 2.0 0.78 644 16 636 15 607 44 106 a39 75,529 45 25 0.68 45,925 0.4821 2.3 10.888 3.4 0.1638 2.5 0.68 2536 49 2514 33 2495 42 102 a40 32,432 220 27 0.89 9526 0.1111 2.3 0.936 2.6 0.0611 1.2 0.88 679 15 671 13 644 27 105 a41 7558 70 6 0.22 2853 0.0860 2.4 0.688 4.1 0.0581 3.3 0.59 532 12 532 17 532 71 100 a42 18,606 70 10 0.26 678 0.1395 2.7 1.262 4.1 0.0656 3.1 0.65 842 21 829 24 794 66 106 a43 9182 84 7 0.47 2633 0.0855 2.7 0.688 3.8 0.0584 2.6 0.71 529 14 532 16 544 58 97 a44 8569 62 5 0.45 3698 0.0862 2.2 0.696 2.9 0.0585 1.8 0.78 533 12 536 12 549 39 97 a46 10,113 8 3 0.07 8276 0.3838 2.1 6.439 3.3 0.1217 2.5 0.64 2094 38 2038 30 1981 45 106 a47 5441 39 3 0.82 1277 0.0775 2.6 0.602 4.0 0.0564 3.1 0.63 481 12 479 16 467 69 103 a48 5184 26 3 0.99 1953 0.1056 2.6 0.885 3.9 0.0608 2.9 0.67 647 16 644 19 632 63 102 a50 6193 36 3 0.27 2338 0.0817 2.7 0.634 12.7 0.0563 12.5 0.21 506 13 499 51 465 276 109 a51 5796 26 3 1.46 9177 0.1068 2.5 0.923 4.1 0.0627 3.2 0.61 654 16 664 20 698 69 94 a52 2492 11 2 1.38 3805 0.1268 3.1 1.152 6.3 0.0659 5.4 0.50 770 23 778 35 803 113 96 a53 151,998 79 34 0.39 18,960 0.4027 2.7 7.345 2.8 0.1323 0.8 0.95 2181 50 2154 25 2129 15 102 a54 32,675 159 17 0.86 4171 0.1007 2.3 0.854 3.0 0.0615 1.9 0.78 619 14 627 14 657 40 94 a55 29,805 150 14 0.74 2314 0.0862 2.3 0.692 3.3 0.0582 2.4 0.69 533 12 534 14 538 53 99 a57 7665 38 4 0.35 1391 0.0964 2.7 0.782 5.5 0.0589 4.8 0.49 593 15 587 25 562 104 106 a58 11,911 50 5 0.09 1893 0.0946 2.6 0.790 7.1 0.0606 6.6 0.36 583 14 591 32 624 143 93 a59 7503 41 3 0.32 13,017 0.0824 2.3 0.653 2.8 0.0574 1.6 0.82 511 11 510 11 508 35 101 a60 17,310 35 6 1.27 464 0.1422 2.8 1.282 12.8 0.0654 12.5 0.22 857 22 838 76 787 261 109 a62 13,709 66 6 0.41 3219 0.0869 2.3 0.697 3.2 0.0581 2.1 0.73 537 12 537 13 535 47 100 a63 119,173 65 23 0.87 2784 0.3031 2.5 4.753 2.9 0.1137 1.6 0.84 1707 37 1777 25 1860 29 92 a64 9894 44 4 0.39 992 0.1004 2.3 0.846 3.9 0.0611 3.1 0.61 617 14 623 18 643 66 96 a65 20,535 74 8 0.73 10,216 0.1002 2.5 0.831 2.9 0.0601 1.5 0.86 616 15 614 14 608 33 101 a66 18,823 28 6 1.27 25,546 0.1720 2.4 1.740 2.6 0.0733 1.0 0.92 1023 22 1023 17 1023 21 100

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Fig.3. CLimagingofrepresentativezirconswithanalyticalsitesandtheirresultingagesindicated,ofsamplePNC2(GreywackeoftheBeirasGroup;lateNeoproterozoic). AnalysisspotsandagesarelistedinTable2.

andArchean(9%;c.3.5–2.5Ga)(Figs.5Aand7).The

Neoprotero-zoicpopulationisdominatedby Cryogenianzircongrains (55%,

c.833–632Ma),followedbyEdiacaran(16%,c.630–550Ma)and

fewTonian(3%,c.914–900Ma)ages.Plottedonaprobability

dia-gram,theNeoproterozoicgroupshowstwomainageclustersatc.

686Maandc.637Ma(Cryogenian),andotherlesssigniﬁcantpeaks

atc.763Ma(Cryogenian), c.591Maand c.565Ma(Ediacaran).

Theyoungestzirconprovidedyieldsof549.6±4.4Ma(Late

Edi-acaran;99.5% concordance),theoldestgrainproviding c.3.4Ga

(Paleoarchean). The youngest population averageagewas

esti-mated, using six younger zircon ages, at 560.3±6.6Ma (Late

Ediacaran;2,MSWD=0.87,Probability=0.35)(Fig.5A).

InsamplePNC2,zirconsaremedium-sized(100–150␮m),

rang-ingfrompinktocolourlessandfromprismatictorounded.Theyare

mostlyanhedralandeuhedralgrainsarerare.CLimagingshows

thatmostgrainsarecompositebuttherearealsosimplezircons

(Fig.3).Mostofthecompositegrainshavecoresofvariablesize

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Fig.4. CLimagingofrepresentativezirconswithanalyticalsiteswithanalyticalsitesandtheirresultingagesindicated,ofsamplePNC3(QuartziteoftheSarnelhaFormation; EarlyOrdovician).AnalysisspotsandagesarelistedinTable3.

alsocoressurroundedbymultipleovergrowths(2a-41,a-36).

Sim-plezirconsarestubbyorshowconcentricoscillatoryzoning(2a-52,

2a-63,2a-58),withatypicallowluminescence(highUcontent)

zonesinthecentreofthecrystal.Therearealsostubbyeuhedral

prisms,grainswithweakconcentricgrowthzoning(2a-20,a-53;

2a-61)withaverylowluminescenceandgrainswithfaint

con-centriczoning(a-10,2a-15).Othertypesofelongatedandnarrow

euhedraltosubhedralprisms(a-40;2a-27,2a-24,a-51)showa

bandedzoneinthecentreandconcentriczoningattherims.

InsamplePNC2,118targetswereanalysed,with102zircon

spotsshowing90–110%concordance.Theseﬁndings(Fig.5B)are

quitesimilartothosewithsamplePNC1withslightdifferencesin

percentagesforpre-Neoproterozoicagesandwithintheagecluster

distributionfortheNeoproterozoicpopulation(Fig.7).

ThezirconpopulationofsamplePNC2showsthefollowingage

distribution:Neoproterozoic(77%,c.992–563Ma),

Mesoprotero-zoic(8%,c.1.2–1.0Ga),Paleoproterozoic(10%,c.2.2–1.7Ga),and

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Fig.5. U–PbConcordiaplotsofzircongrainsfromsamplesPNC1andPNC2oftheBeirasGroup(forlocationsofthesamplesseeFig.1).ConcordiaplotsA1andB1showing allanalyses.ConcordiaplotsA2andB2showingtheNeoproterozoicages.A3andB3showtheagesoftheyoungerzirconpopulationsofthelateNeoproterozoicgreywackes.

NeoproterozoicpopulationofsamplePNC2isdominatedby

Cryo-genianzircongrains(52%,845–631Ma),withtwoageclustersatc.

796Maandc.660Ma,andanothersmallerpopulationatc.723Ma.

Tonianages(8%,c.992–865Ma)showanageclusteratc.942Ma

(Figs.5B,7and8).TheEdiacaranpopulation(18%,c.630–563Ma)

populationischaracterisedbytwoageclustersatc.616Maand

588Ma.Theyoungestzirconwasdatedat562.5_±6.1Ma(Late

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Fig.6. U–PbConcordiaplotsofzircongrainsfromsamplesPNC3andPNC4oftheSarnelhaandArmoricanQuartziteformationsrespectively(forlocationsofthesamples seeFig.1).ConcordiaplotsA1andB1showingallanalyses.ConcordiaplotsA2andB2showingtheNeoproterozoic,CambrianandOrdovicianages.A3showstheagesofthe youngerzirconpopulationsoftheSarnelhaFormationquartziteandB3showstheyoungestageyieldedbytheArmoricanquartzite.

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Fig.7.ProbabilityplotsandpiediagramsofdetritalzirconU–PbagepopulationsfromlateNeoproterozoicgreywackes(PNC1andPNC2,atthebottom)andEarlyOrdovician quartzites(PNC3andPNC4,atthetop)ofSWCIZsamplesanalysedinthisstudy.

Theyoungestpopulationwasestimatedat578.5±4.7Ma(Late

Edi-acaran;2,MSWD=0.85,Probability=0.36)(Fig.5B).

3.2.2. OrdovicianquartzitesofSarnelhasandPenacova(PNC3

andPNC4)

ThezirconpopulationofsamplePNC3isdominatedbymedium

tolarge(120–220␮m)grains,rangingfromtransparentcolourless

totranslucentpink,andmorerarelybrown.Twogroups canbe

distinguished:onegroupwitheuhedraltosubhedralprismaticto

pyramidalcrystalforms,andanothergroupwithmoreroundedand

stubbyforms.Thissampleincludesmoreelongatedcrystalswith

novisiblefaceswhencomparedwithgreywackesamplesPNC1

andPNC2.CLimagingrevealsawidevarietyofformsandinternal

structureswithcompositeandsimplegrains(Fig.4).Composite

zir-consincluderoundedorirregularlyshapedcores(a-62,a-33),that

aretypicallyverysmall(a-6,a-54,2a-33).Zoningpatternsinthe

stubbysimplegrainsrangefromclear(a-52,2a-66,2a-18,2a-42),

toweak(2a-16)concentricﬁne(a-31)oscillatoryzoning.Grain

a-57/a-52isasimplecrystalwithsector-growthzoning,affectedby

ahighluminescencerecrystallisationfront.CLimagingalsoshows

prismaticandnarrowcrystalscharacterisedbythinbandedzoning

withmoderateluminescencecontrast(2a-2)truncatedbydiffuse

recrystallisationfronts(2a-11,2a-24)(Fig.4).Mostofthezircons

fromsamplePNC4(95%),aquartzitefromtheArmoricanQuartzite

Formationareﬁne-tomedium-grained(80–110␮m).Zircongrains

rangefromtransparentcolourlesstotranslucentandslightlypink.

Mostareelongatedeuhedraltosubhedralprismsorstubby

subhe-dralwithsmoothcrystallinefaces.

Thezirconagesobtainedfor PNC3 andPNC4areshownin

Fig.6(Tables3and4).Thedistributionofagepopulationsfound

inthearkosicquartziteoftheSarnelhasFormation(samplePNC

3)isdifferentfromthetwosamplesoftheBeirasGroup(samples

PNC1andPNC2).60%ofzirconagesofsamplePNC3are

Neo-proterozoic(outofapopulationof120analysedtargets,113have

90–110%concordance)(Figs.6–8).TheNeoproterozoicpopulation

is dominated by: Ediacaran zircongrains (36%, c.627–544Ma)

withtwomainageclustersatc.609Maand582Ma,Cryogenian

(23%,c.798–633Ma)andrare Tonian(1%, c.908Ma)ages.The

pre-Neoproterozoic record consistsof Paleoproterozoic (17%, c.

2.4–1.7Ga),Archean(5%,c.2.8–2.5Ga)andMesoproterozoic(1%,

only1grain,c.1.1Ga).EarlyPaleozoicagesaredominatedby

Cam-brianages (14%,c.542–489Ma),whereasOrdoviciangrainsare

scarce(3%, c.486–484Ma).Theyoungestzirconprovided yields