HAL Id: insu-01574690
https://hal-insu.archives-ouvertes.fr/insu-01574690
Submitted on 16 Aug 2017
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
southern France
Maxime Padel, José Javier Álvaro, Sébastien Clausen, François Guillot, Marc Poujol, Martim Chichorro, Eric Monceret, M. Francisco Peirera, Daniel
Vizcaïno
To cite this version:
Maxime Padel, José Javier Álvaro, Sébastien Clausen, François Guillot, Marc Poujol, et al.. U–
Pb laser ablation ICP-MS zircon dating across the Ediacaran–Cambrian transition of the Mon- tagne Noire, southern France. Comptes Rendus Géoscience, Elsevier, 2017, 349 (8), pp.380-390.
�10.1016/j.crte.2016.11.002�. �insu-01574690�
Petrology, Geochemistry (Geochronology)
U–Pb laser ablation ICP-MS zircon dating across the Ediacaran–Cambrian transition of the Montagne Noire, southern France
Maxime Padel
a,*, J. Javier A´lvaro
b, Se´bastien Clausen
a, Franc ¸ois Guillot
c, Marc Poujol
d, Martim Chichorro
e, E´ric Monceret
f, M. Francisco Pereira
g, Daniel Vizcaı¨no
haUMR8198EEPCNRS,universite´ deLille-1,baˆtimentSN5,avenuePaul-Langevin,59655Villeneuve-d’Ascqcedex,France
bInstitutodeGeociencias(CSIC-UCM),Novais12,28040Madrid,Spain
cUMR8187LOGCNRS,universite´ deLille–universite´ duLittoralCoˆted’Opale,SN5SciencesdelaTerre,59655Villeneuve-d’Ascqcedex, France
dGe´osciencesRennes,UMR6118,universite´ deRennes-1,campusdeBeaulieu,35042Rennes,France
eGEOBITEC/DepartamentodeCieˆnciasdaTerra,UniversidadeNovadeLisboa,Portugal
f18,ruedesPins,11570Cazilhac,France
gIDL/DepartamentodeGeocieˆncias,ECT,UniversidadedeE´vora,Portugal
h7c/oJean-BaptiseChardin,Maquens,11090Carcassonne,France
C.R.Geosciencexxx(2017)xxx–xxx
ARTICLE INFO
Articlehistory:
Received28July2016
Acceptedafterrevision25November2016 Availableonlinexxx
HandledbyMarcChaussidon
Keywords:
Ediacaran Cambrian U–Pbdating MontagneNoire
ABSTRACT
U–Pblaserablationinductivelycoupledplasmamassspectrometrywasusedfordating zircongrainsextractedfrom foursedimentaryand volcanosedimentaryrocks ofthe MontagneNoire encompassingthe presumedEdiacaran–Cambrianboundaryinterval.
MagmaticzirconfromtwosamplesfromthebasalandmiddlepartsoftheRivernous Formation(arhyolitictuff)weredepositedat542.51Maand537.12.5Ma,bracketing the541MaagepresentlyadmittedasbeingattheEdiacaran–Cambrianboundary.Inaddition, apieceofsandstonefromtheunderlyingRivernousFormationcontainingmostlyeuhedral zircongrains,suggestingproximalmagmaticsources,yieldsNeoproterozoicdatesranging from574Mato1Ga,and subsidiaryolderdatesfrom1.25 to2.75Ga.Anotherpieceof sandstonefrom the overlyingMarcoryFormation yielded mostly roundedzircongrains probablyissuedfrommoreremoteareas,withalargespectrumdominatedbyNeoproterozoic datesaswellasolderagesupto3.2Ga.Acomparisonofbothkindsofsandstonesuggestsa significantchangeinprovenance,changingfromarestrictedsourceareaduringtheEdiacaran toamuchlargersourcedomainduringtheCambrianEpoch2thatrecordedcontributions fromdifferentcratonsofGondwana.
C 2017Acade´miedessciences.PublishedbyElsevierMassonSAS.Thisisanopenaccess articleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/
4.0/).
* Correspondingauthor.
E-mail addresses: maxime.padel@etudiant.univ-lille1.fr (M. Padel), jj.alvaro@csic.es (J.J. A´lvaro), sebastien.clausen@univ-lille1.fr (S. Clausen), Francois.Guillot@univ-lille1.fr(F.Guillot),marc.poujol@univ-rennes1.fr(M.Poujol),ma.chichorro@fct.unl.pt(M.Chichorro),eric.monceret@orange.fr (E´.Monceret),mpereira@uevora.pt(M.F.Pereira),daniel.vizcaino@wanadoo.fr(D.Vizcaı¨no).
GModel
CRAS2A-3348;No.ofPages11
ContentslistsavailableatScienceDirect
Comptes Rendus Geoscience
w ww . sc i e nce d i re ct . co m
http://dx.doi.org/10.1016/j.crte.2016.11.002
1631-0713/C 2017Acade´miedessciences.PublishedbyElsevierMassonSAS.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://
creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
The pre-Variscan succession of the Montagne Noire cropsoutasafold-and-thrustcomplexdividedintotwo sedimentary-dominated, northern and southern flanks fringinganessentiallymetamorphic,AxialZone(Arthaud, 1970; Ge`ze, 1949). Several tectonic models have been proposedfortheMontagneNoireandarestillsubjectof debate(BrunandVanDenDriessche,1994;Charlesetal., 2009; Faure and Cottereau, 1988; Fre´ville et al., 2016;
Mattaueretal.,1996;Poujoletal.,inpress;Soulaetal., 2001;VanDenDriesscheandBrun,1992).ThePrecambri- an–Cambrianboundaryhastraditionallybeententatively located in the lowermost formation exposed in the southernMontagneNoire,namelytheMarcoryFormation (A´lvaro et al., 1998). However, recent reviews of the northernsuccessionschallengedtheformerstratigraphic chart (A´lvaro et al., 2014b; Devaere et al., 2013) and establishedalowerstratigraphicpositionforthevolcano- sedimentarysuccessionsoftheGrandmont,Rivernousand Layrac formations, exclusively exposed in the northern MontagneNoire.Theonlypreviousradiometricdatafrom theRivernousFormation(Fm.)yieldedanOrdovicianage, ranging from 47319Ma to 44340 (Rb/Sr method;
Demange, 1982), which was subsequently ruled out by biostratigraphicagesyieldedbyacritarch-bearing,laterally equivalent deposits (the so-called ‘‘Schistes X’’) from the Axial Zone (Fournier-Vinas and Debat, 1970). There, the
‘‘SchistesX’’arecappedbytheSe´rie`sTuff(‘‘Se´rie`s’’isavillage name) tentatively correlated withthe Rivernous Fm. The Se´rie`sTuffwasdatedat54515MabyPb-evaporationon zircon from a metadacite (Lescuyer and Cocherie,1992).
Somescarcezirconcrystalsweresampledinagarnet-grade Cambrianmeta-siltstonefromthesouthernMontagneNoire, givingamaximumdepositionalageof556Mabasedonlyon asinglezircon(Gebaueretal.,1989).Thisageattributionmay lookdisputable,giventhemorerecentstatisticalguidelines for provenance studies (see below) and also taking into accountthemarkedmetamorphiccharacterofthisrock.In fact,inapreviouspaper,GebauerandGru¨nenfelder(1977) admittedthatabout80%oftheprimitiveradiogenicPbmight havebeenlostduetoPhanerozoicthermalevents.Inorderto improvethestratigraphicframeworkoftheNeoproterozoic–
Cambrian boundary interval, and the lithostratigraphic nomenclaturallinksbetweentheAxialZoneandthenorthern andsouthern flanksofthe MontagneNoire,zircon grains weresampledfromtheRivernous,GrandmontandMarcory formationsanddatedbyinsituLA-ICP-MSU–Pbanalysis.Our results place new constraints upon the palaeogeographic affinitiesofthedifferenttectonostratigraphicunitsthatform theMontagneNoire,aswellasonthedetritalprovenanceof theEdiacaran–Cambriansedimentspreservedinneighbour- ingtectonostratigraphicareas.
2. Geologicalandstratigraphicsetting
LocatedinthesouthernpartoftheFrenchMassifCentral (Fig.1A),theMontagneNoirerepresentsasegmentofthe external,southwesterncomponentoftheVariscanBeltin Europe(Demange,1998;Poujoletal.,inpress;Rogeretal., 2004).Assummarizedabove,thisENE–WSW-strikingrange
isdividedintothreetectonicunits:acentralmetamorphic dome,theso-calledAxialZone,fringedbyitsnorthernand southernflanks(Demange,1985;Ge`ze,1949).
TheAxialZoneisessentiallycomposedofmicaschist, minor marble, paragneiss and migmatized orthogneiss (Ge`ze,1949).Theprotolithageoftheorthogneissandits relationshipwiththemetasedimentaryrocks havebeen disputed.Some authorsinterpretedtheorthogneissasa granitic Precambrian basement(Demange, 1975, 1998), whereas others considered it as Palaeozoic intrusions (BardandLoueyit,1978).Recentconventional(ID-TIMS), SHRIMP and LA-ICP-MSU–Pb datings of various ortho- gneisssamples(Cocherieetal., 2005;Pitraet al.,2012;
Rogeretal.,2004)suggestthatthegraniticprotolithwas emplacedduringtheOrdovician.
The southern and northern sedimentary-dominated flanksoftheAxialZoneareafold-and-thrustcomplexof nappes (Fig. 1). The Precambrian–Cambrian boundary interval, only reported in the northernMontagne Noire (A´lvaro et al., 2014b), comprises four formations, from bottom to top, the Grandmont, Rivernous, Layrac and Marcou formations (Fig.2). The Grandmont Fm., about 700m thick, consists of grey to black shales with subsidiary sandstone interbeds (Fig. 2). The Rivernous Fm.,upto200mthick,comprisesslightlymetamorphosed rhyolitictuffsthatincluderarebrecciaandshaleinterbeds (Fig.2). Both formationscropout in theAve`ne–Mendic parautochthon,whichincludestheLode´voisinlierandthe Lacaunethrustslice(Murat,Fig.1B).IntheLacauneunit,a lateral equivalent of the Rivernous Fm. (locally named Murat Fm.), withbase andtop truncatedbyfaults,was datedat53212Ma(U–Pbonzircon;Demangeetal.,1995;
Ducrot etal., 1979). In the Ave`ne–Mendic parautochthon (Fig.1),therhyoliticpalaeoreliefformedbytheRivernous Fm.(uptoabout300mhigh,afterA´lvaroetal.,2014b)is unconformably onlapped by the volcano sedimentary conglomerates andsandstones ofthe Layrac Fm.(Fig. 2).
TheLayracFm.isitselfoverlainbythecarbonate-dominated MarcouFm.,about400mthickandassignedtotheCambrian Stage2byrecentbiostratigraphic studies (Fig.2,Devaere etal.,2013).
Theabove-reportedformationsarenotexposedinthe southern Montagne Noire, where the oldest outcrop is represented by the up to 1000m-thick Marcory Fm.
(Fig. 2), a monotonous alternation of sandstones and shaleswithsubordinatecarbonatenodulesandlayers.The upperpartoftheMarcoryFm.hasbeenassignedtothe CambrianStage2–3transitionduetotheoccurrenceofthe ichnogenera Psammichnites and Taphrelmintopsis(A´lvaro andVizcaı¨no,1999),andtheoldesttrilobitesfoundinthe Montagne Noire, i.e. Blayacina miqueli (Cobbold, 1935;
Geyer, 1992). The Marcory Fm.,although absentin the Ave`ne–Mendicparautochthon,isexposedinotherthrust slicesandnappesofthenorthernMontagneNoire.
3. Materialandmethods 3.1. Material
TheGrandmontandRivernousFormationshavebeen sampledat their stratotype,along theRivernousrivulet
(about4kmtotheeastofLode`ve):asandstonefromthe baseoftheexposedGrandmontFm.(sampleMN1),anda rhyolitictufffromthebaseoftheRivernousFm.(sample MN2).TheRivernousFm.wasalsosampledatitsmiddle partneartheColduLayrac(sampleMN3).MN1toMN3 samplesbelongtotheso-calledAve`ne–Mendicparautoch- thon.InordertoinvestigatetheprovenanceoftheMarcory Fm.,asandstone(sampleMN4)wasalsoselectedfromthe Psammichnitesgigas-bearinglevelinthesouthernMonta- gneNoire (A´lvaroand Vizcaı¨no,1999), along theOrbiel riversectionoftheMinervoisnappe(Fig.1).
3.2. Samplespreparation
Zirconseparationfromfreshsamplesstartedwithrock grindingusingasteelcrusher.Theresultingpowderswere sievedintherangeof50–250
m
m.Grainswereseparated first usinga heavyliquid (sodiumheteropolytungstates, density 2.85gcm–3), then using a Frantz magnetic separator.FollowingSla´maandKosˇler(2012),theselected grainswereobtainedfromrandomhandpickingundera binocularmicroscopewhatevertheirsize,shape,orcolor,inordertoavoidanyoperatorbias.Theywerefinallysetin anepoxyresinpuckandpolishedtoexposetheircore 3.3. LA-ICP-MSinsituU–Pbdating
Toidentifyinternalgrowthtexturesandmorphologies, zircongrainswereimagedbyscanningelectronmicroscopy (SEM) to get cathodoluminescence and back-scattered electron images(at the ‘‘Laboratoired’oce´anologie et de ge´osciences’’,UniversityofLille,France).TheU–Pbagesof zirconsweredeterminedinsituattheGe´osciencesRennes laboratorybyLA-ICP-MS usinganICP-MS Agilent7700x coupled with an ESI laser Excimer system producing a radiationwithawavelengthof193nm(NWR193UC),with ablationspotdiametersof25
m
m,energypulsesof7Jcm–2, andrepetitionratesof 5Hz. Ablationswere operatedon both grain rims and cores. Where necessary, distinct domainsofazircongrainwereanalyzedtocomparetheir ages.TheresultingablatedmaterialwasmixedinaHe,N andArgasmixturebeforebeingtransferredintotheplasma sourceoftheICP-MSdevice.Eachanalysislasted80sand consisted of a first 20-s background measurement Fig.1.SimplifiedgeologicalmapoftheMontagneNoire;modifiedfromDevaereetal.(2014).A,LocationoftheFrenchMassifCentral(grey)andMontagne Noire(rectangle)inFrance.B,Structuralunitsandpreviousradiometricages(a)Demange,1982(Rb/Sr)discardedbyourresults(seetext);(b)Ducrotetal., 1979(U–Pb)inDemangeetal.,1995;and(c)LescuyerandCocherie,1992(U–Pb).M.Padeletal./C.R.Geosciencexxx(2017)xxx–xxx 3
GModel
CRAS2A-3348;No.ofPages11
followed by 60-s ablation with measurements of
204(Hg+Pb), 206Pb, 207Pb, 208Pb, 232Th, and 238U, and a 15swash-outdelaybeforethenextacquisition.Thedata werecollectedinbatchof43analysesdividedinthreesetsof 10unknowns,bracketedbytwomeasurementsoftheGJ-1 primaryzirconstandard(Jacksonetal.,2004)tocorrectfor U–Pb and Th–Pb laser-induced fractionation and for instrumentalmassdiscrimination,followedbyoneanalysis ofthe Plesovicesecondary zirconstandard(Sla´maet al., 2008)inordertochecktheprecisionandaccuracyofthe measurements. During the course of this study, the Plesovice zircon standard yielded a Concordia age of 336.80.67Ma (N=32). The operating conditions for the LA-ICP-MSequipmentcanbefoundinSupplementaryTable 1. For more information on the acquisition protocol, see Manzottietal.(2015).Datatreatmentwasperformedwiththe GLITTERsoftware(VanAchterberghetal.,2001)andplotted using the Isoplot 3.75 software (Ludwig, 2012) in both Wetherill and Tera-Wasserburg Concordia diagrams. For rhyolitictuffs, theages were calculated usingtheTuffZirc Agealgorithm(LudwigandMundil,2002)togetherwiththe SambridgeandCompston(1994)algorithm.Forthesandsto- nes,agedistributioncurveswithprobabilitydensityplotwere obtained using the density plotter freeware proposed by Vermeesch(2004).Fordates>1Ga,wereportedthe207Pb/
206Pbdatesandforages<1Ga,weusedthe206Pb/238Udates.
The analyses out of the [90–110%] concordance interval, calculatedwith 100(207Pb/235Uage)/(207Pb/206Pbage)for ages>1Ga(Meinholdetal.,2011)and100(206Pb/238Uage)/
(207Pb/235Uage) for ages<1Ga, were rejected(Faure and Mensing, 2005 and Talavera et al., 2012). The age of the youngestzirconpopulationisderivedfromaclusterofatleast threeanalysesfromthreedifferentgrainsoverlappinginageat 2
s
(standarddeviation),asproposedbyDickinsonandGehrels(2009) to ensure a statistically robust estimate of the maximum depositional ages. Percentages of concordance, isotopicratiosandageswith1
s
errors,aswellasUandPb concentrations are providedin Supplementary Table 2. In sedimentaryrocksamples(MN1andMN4),about110grains wereanalyzedinordertogetthebestrepresentationofthe detritalzirconpopulations.Fortuffs(MN2andMN3),about 50grainswereanalyzed,followingthesuggestionsofBowring etal.(2006),togivearobustestimateofthebestageforthe relatedvolcanicevent(s).4. Results
4.1. GrandmontFormation(MN1)
ZirconsfromthesampleMN1,medium-grainedsand- stone, are mostly in the 100–250
m
m range, euhedral, facetted,rarelysub-rounded,colourlessandgenerallywell zoned(Supplementarydata,Fig.S1).107ofthe114MN1 analyseswereconcordant[90–110%],amongwhich 94%are Neoproterozoic (101 grains), 3% Mesoproterozoic (3 grains), 2% Paleoproterozoic (2 grains) and 1 grain (1%)isArcheaninage(Fig.4B).Intheintervalrangingfrom 500to1100Ma,theprobabilitycurveshowsadominant Ediacaran groupwithin thecluster 550–850Ma, which displaysamainpeakaround605Maandasecondaryone around 635Ma (Fig. 4B). In this same cluster, four subsidiary peaks are identified around 690Ma, 760Ma, 805Ma and 835Ma. The Tonian-aged zircon grains are characterized by one peak around 906Ma, in an 890–
920Maclusterandanotherpeakaround1Gainthe950–
1050Macluster.Thefouryoungestandconcordantzircon grains from this group ranging from567.26.12Ma to Fig.2. UpperEdiacaran–lowerCambrianstratigraphicchartofthesouthernandnorthernMontagneNoire;modifiedfromA´lvaroetal.(2014b).
579.56.28Ma,yield anaveragedateof5746Ma(95%
conf.,Fig.3E).
4.2. RivernousFormation(MN2andMN3)
Samples MN2 and MN3 are both rhyolitic tuffs.
Accordingly, zircon grainsfromsamples MN2and MN3 areeuhedral, clearand colourless.Rarelycored,internal structures highlighted by the CL-imaging show clear magmaticzoning(Supplementarydata,Fig.S1).
InsampleMN2,59zircongrainswereanalysed,among which 50 gave concordant dates [90–110% as defined above]. Sevenof the 50 analyses were rejected due to possibleleadloss.Thustheyoungestandmainpopulation fromthissamplerepresent65%ofthese43zircongrains with individual 206Pb/238U dates ranging from 534.86.01Mato5466.02Ma.Thesecondgrouprepre- sents23%ofthetotalpopulation,andgives206Pb/238Udates ranging from 576.96.3Ma to 600.86.7Ma (Fig. 3A).
Finally, five inherited core grains were dated at Fig.3.LA-ICP-MSresultsforallsamplesusing206Pb/238Uages.DiagramA:mixtureanalysisforsampleMN2usingSambridgeandCompston’s(1994) approach;theage579.84.3Maisconsideredasinheritedage.DiagramB:mixtureanalysisforsampleMN3usingSambridgeandCompston(1994)approach;
theage5247.2Maisconsideredasgeologicallymeaningless,duetoleadloss.DiagramsCandD:datapointagedistributionforsamplesMN2andMN3,resp., usingTuffZircAge(LudwigandMundil,2002);chosenemplacementagefortherhyolitictuffsoftheRivernousFm.are:5423Ma(2s)forsampleMN2and 5373Ma(2s)forsampleMN3.DiagramsEandF:averageagecalculatedfortheyoungestconcordantzirconpopulationofGrandmontandMarcoryFm.(sample MN1andMN4),derivedfromaclusterofatleastthreeanalysesfromthreedifferentgrainsoverlappinginageat2s(standarddeviation)asproposedbyDickinson andGehrels(2009).
M.Padeletal./C.R.Geosciencexxx(2017)xxx–xxx 5
GModel
CRAS2A-3348;No.ofPages11
651.67.2Ma, 661.87.1Ma, 66237.1Ma, 685.8 7.6Maand704.77.6Ma(Table2).
Lookingattheyoungest population,theTuffZircAge algorithmreturnedadateof542.5+0.7/–0.6Ma,whilethe SambridgeandCompstonalgorithmyieldedacomparable dateof541.92.3Ma(Fig.3AandC).Therefore,choosing between those two within error identical results, we concludethatthisrhyolitictuffwasemplaced542.5+0.7/–
0.6Ma.
InsampleMN3,58zircongrainswereanalysed,among which 52 yielded concordant results [90–110%]: two compositegrainswithcores(Zr1andZr27)yieldingU–
Pbdatesof1837.719.1Ma and583.16.37Marespec- tively. The youngest zircon population suggested by the SambridgeandCompstonapproachforsampleMN3returned adatearound524Ma(Fig.3B),whichispoorlyconstrained, by only one concordant zircon among seven somewhat discordantdatapoints(onaConcordiaplot).Therefore,this dateisinterpretedasgeologicallymeaninglessasitcouldbe linkedtoapossibleleadloss.
Keepingonlyagroupcomprisingthreeconcordantdata points(greybars inFig.3B), theTuffZircAge algorithm yieldeda dateof537.35+2.35/–1.25Ma whiletheSam- bridge and Compston approach returned a comparable date of 537.12.5Ma. This second rhyolitic sample was thereforeemplaced537.12.5Maago(2
s
)(Fig.3BandD).4.3. MarcoryFormation(MN4)
SampleMN4is afine-grainedandmaturesandstone.
Accordingly, its zircon crystals are mostly anhedral, rounded to subrounded, often broken and rarely bi- pyramidal, largely in the 50–100-
m
m size range. They are colourless to yellowish, though the biggest zircon grainsarereddishincolour.Intheanalysedfraction,104of the112MN4analyseswereconcordant[90–110%],among which87% areNeoproterozoic(90 grains),4%Mesopro- terozoic (4 grains), 5% Paleoproterozoic (6 grains), 2%Neoarchean(2grains),onegrainisMesoarcheanandthe oldestoneisPaleoarcheaninageat3.2Ga(Fig.4A).
Theprobabilitydensitycurve(Vermeesch,2004)shows a dominant Ediacaran group (clustered across 550–
850Ma),withamainpeakaround614Maandasecondary peak around 575Ma (Fig. 4A). In this same cluster,six otherpeaksareidentifiedaround651Ma,678Ma,700Ma, 737Ma, 800Ma and 850Ma. The Tonian-aged zircon grainsare characterized by onepeak around 900Ma in an 890–920Ma cluster and another distinctive peak around 1Ga in the 950–1050Ma cluster. The three youngest dates obtained from this sample that are concordantyieldanaveragedateof602.57.3Ma(Fig.3F).
5. Discussion
5.1. TheRivernousvolcanicactivitymarkingthe Precambrian–Cambrianboundaryinterval
Thetwodates (537.12.5Ma and542.5+0.7/–0.6Ma) obtainedfrom theRivernousrhyolitictuffsaremucholder than previously estimated (47319Ma and 44340Ma;
Demange,1982).Theseresultsallowustoconfidentlyidentify the Precambrian–Cambrian boundary (541Ma, Gradstein etal.,2012)inthebasalsuccessionoftheMontagneNoire.
By comparisonwith thepreviouslydetermined ageofthe Se´rie`sTuffsfromtheAxialZone(54515Ma;Lescuyerand Cocherie,1992)andtheRivernous(formerMurat)Fm.inthe Lacaune thrust slice of the northern flank (53212Ma, intercept superior; Demange et al., 1995 and references therein;Figs.1–2),theseresultssupportthelateralequiva- lenceoftheSe´rie`svolcanicepisode(AxialZone)andRivernous rhyolitictuffdeposition(northernflank),asalreadysuggested (Poucletetal.,inpress).
InotherVariscanunitsoftheIbero-ArmoricanArc,some plutonicbodieshaverecentlybeendatedaround540Maby LA-ICPMS(Supplementarydata,Fig.S2;seealsoCasasetal., 2015;Castin˜eirasetal.,2008;Gutie´rrez-Alonsoetal.,2004;
Melletonetal.,2010;Rubio-Ordo´n˜ezetal.,2015):theArc- de-FixandArde´choisaugengneissesintheMassifCentral, with respective Concordia age of 541.83.1 and 542.53.1Ma (Couzinie´ et al., this issue), aswell asthe LaparanorthogneissintheCentralPyrenees,withaConcordia age of 5453Ma (Mezger and Gerdes, 2016). All these plutonicandvolcanicevents,overlappinginagewithinerror, shouldbelinkedtoacommonepisodeassociatedwiththe voluminousmagmaticandanatecticCadomianeventsrepor- tedforWestGondwana,amongothers,byLinnemannetal.
(2007, 2008). According to these authors, the numerous plutonic and volcanic to volcano sedimentary complexes identified in the Ossa-Morena, Saxo-Thuringian and Anti- Atlaszones(A´lvaroetal.,2014a;Bleinetal.,2014)canresult fromaslabbreakoffofasouthwardsubductedoceanicplate endingwiththeCadomiancycleatabout545–540Ma.The endofthePan-African/Cadomiancycleledtotheonsetofa Cambrian magmatic cycle (Supplementary data, Fig. S2), relatedtotheriftingoftheNorthGondwanamargin(A´lvaro etal.,2014a,2014b;Poucletetal.,inpress).
5.2. AgeandpotentialprovenancesoftheGrandmontand Marcoryformations
Depositionalages.Theyoungestgroupofconcordant zircongrainsfromtheGrandmontFm.(sampleMN1)yield anaveragedateof5746Mathatisinterpretedhereasits maximumdepositionalage(i.e.lateEdiacaran;Fig.3E).This resultiscoherentwiththestratigraphicframeworkproposed byA´lvaroetal.(2014b)andtheNeoproterozoicagebasedon acritarchs reportedfromthe‘‘SchistesX’’Fm.oftheAxial Zone (Fournier-Vinas and Debat, 1970). As a result, this maximum age of deposition supports their correlation betweentheGrandmontand‘‘SchistesX’’formations(A´lvaro etal.,2014b).
Theaveragedatecalculatedfromtheyoungestgroupof concordant data for the Marcory Fm. at 602.57.3Ma (Fig.3F)mightbeconsideredasamaximumdepositionalage.
However, it is far from the real depositional age, as mentioned above. Indeed, this sample wasselected from the Psammichnites gigas-bearing level (Fig. 2), andconse- quently must be assigned to the Cambrian Stage 2–3 transition,i.e.itislessthan521Maold.
Sourceofthepre-ca.1Gadetritalzircongrains.The age spectraobtained forthesamples fromtheMarcory
(MN4)and Grandmont(MN1)formationsaresomewhat similar, but display some differences. Although each individualsingleton-dateshouldbetreatedwithcaution, thedistributionsofpre-1Gaagesareplainlydistinct(Figs.
4and5).
Asmentioned above,zircon grainsfromtheMarcory Fm.(sampleMN4)aremuchsmalleranddefinitelymore rounded(Supplementarydata,Fig.S1)thanthosefromthe GrandmontFm.(sampleMN1),suggestingalongdistance oftransportfortheformergrains.Wehaveseparateddata frominheritedcores(whiteboxesinFig.4),meaningless regardingthesourceage,fromdatafromzonedmagmatic
rims(blackboxes,Fig.4)thatrepresentmostprobablythe ageofthesource-rock.Fromthisrespect,theoldestzircon rim from the Grandmont Fm. (MN1) is only Late Paleoproterozoic(180619Ma),andonlytwograinrims are older than 1 Ga. Bycontrast, the presenceof several ArcheanzirconrimsinMN4pointstoamajorchangeinthe sourceareas.MN1zircongrainscouldpossiblybederived, ultimately,fromtheAmazoniancraton(Rhyacian,Orosirian andStatherianevents),moreprobablyfromtheEburnean WestAfricancraton,orfromtheSaharanmetacraton(Fig.5).
Bycontrast, eight pre-1Gazircon rimsfromsample MN4 form a Paleoproterozoic group (cluster ranging from Fig.4. Frequencyandprobabilitydensityplotsofdetritalzircongrainsintherange500–3300MaforsamplesMN1(B)andMN4(A).Agegroupsofeach samplearepresentedinapiediagram.SectionCshowsacomparisonofagegroupswherewhiteboxesrepresentdatesfrominheritedcoreandblackboxes relatetodatesfromzonedrims.
M.Padeletal./C.R.Geosciencexxx(2017)xxx–xxx 7
GModel
CRAS2A-3348;No.ofPages11
210919Mato178720Ma)andanArcheangroup.Those groupsfitmuchbetter withan African sourcecomprising EburneanareasplusArcheanWestAfricancraton(Fig.5).
However,weshouldnotexcludethattheavailabilityof zircon to erosion and transport from either primary crystallineor recycledsources requires that thezircon- bearing rocks be exposed at the appropriate time, and recyclingfromoldersedimentarydepositsmayconstitute a moresignificantsourcethan fromprimary crystalline rocks.
SourcesoftheStenian–Tonian detritalzircons.The clusterpointingtotheStenian–Toniantransition(950to 1100Ma)insamplesMN1andMN4couldshareacommon origin(Fig.4). One shouldexpectan Amazoniancraton affinity (Linnemann et al., 2011) with detrital sources relatedtotheSanIgnacio andSunsas eventsand onits eastern margin (Pereira et al., 2012). However, many studies on sandstones from Lower Palaeozoic peri- GondwananexposuresaroundtheMediterraneanregion (e.g.,Israel,Jordan,Libya,Pyrenees,Sardinia,Greeceand Sicily) rule out an Amazonian provenanceand suggest insteadaneasterntosoutheasternAfricanorigin(Altumi et al., 2013; Avigad et al., 2003; Avigad et al., 2012;
Kydonakisetal.,2014;Margalefetal.,inpress;Meinhold etal.,2011;Meinholdetal.,2013;Williamsetal.,2012).
Therefore,theArabian–Nubianshield,theSaharanmeta- craton, possibly the western edge of the Congo craton (Tacketal.,2001),aswellasitseasternpartrecordingthe
‘‘KibaranEvent’’(Tacketal.,2010)andtheIrumidebelt (Meinhold etal., 2011),fit wellas potentialsourcesfor
MesoproterozoicandStenian–Tonianzircongrains.These zircon-formingevents occurredsimultaneouslywiththe assembly of the supercontinent Rodinia (Grenvillian orogeny). Different hypotheses have been advanced to explainthisinputofMesoproterozoicandStenian–Tonian zircon crystals (Altumi et al., 2013), including: (i) the transportoflargeamountsofsedimentthroughNeopro- terozoicglaciersfollowinganoriginalsouth–northtran- sect, laterreworkedanddeposited(Avigad etal.,2003);
and (ii) a source region linked to theTransgondwanan supermountain range resulting from the East African–
AntarcticOrogenandformedduringtheprotractedLate Neoproterozoic docking of East and West Gondwana (Williamset al., 2012), involving thedevelopment of a super-fan system (Kydonakis et al., 2014; Squire et al., 2006).
SourcesofNeoproterozoicdetritalzircons.Neopro- terozoic grains display similar age distributions in the GrandmontandMarcoryformations:amainNeoprotero- zoic populationof zircon grains(with onepredominant Ediacarangroup)followedbyfivesimilarpeaksacrossthe Tonian–Cryogenianinterval(Fig.4).Potentialsourcesfor thesedetritalzirconsarelocatedintheeastern(Saharan metacraton,Arabian-Nubianshield)andwestern(Trans- Saharan belt,Pan-African sutureoftheAnti-Atlas, early and late Cadomianarcs,and Avalonian Arc)area ofthe North-Gondwanamargin(Fig.5).Theprobabilitydensity curve of the Marcory Fm., as well as the shape and roundnessofitszircongrains,impliesmoreremoteorigins forthemthanfortheGrandmontFm.ones. Therefore,a Fig.5. PotentialsourcesforsamplesMN1andMN4(modifiedafterDrostetal.,2011;Linnemannetal.,2011;Pereiraetal.,2011;Pereiraetal.,2012;Tack etal.,2001;Tacketal.,2010).AC1:SiderianeventoftheAmazoniancraton;AC2:Rhyacian,OrosirianandStatherianeventsoftheAmazoniancraton;AC3:
SanIgnacioandSunsaseventsoftheAmazoniancraton;AC4:easternmarginoftheAmazoniancraton;Av:Avalonia;Cd:Cadomia;Bo:Bohemianmassif;
AA:Anti-Atlas;WAC1:EburneaneventoftheWestAfricancraton;WAC2:LiberianeventoftheWestAfricancraton;WAC3:LeonaneventoftheWest Africancraton;TSB1:Trans-Saharanbelt,Benin-Nigerianshield;TSB2:Trans-Saharanbelt,Tuaregshield;SMC:Saharanmetacraton;ANS:Arabian–Nubian shield;CC:Congocraton.
comparison ofthemorphologicaland agedifferencesof thesezircon grainssuggestsanevolutionof thedeposi- tional basinand it sourcing from a narrowbasinbeing infilledbytheGrandmontFm.,probablyaback-arcbasin resulting from the Panafrican/Cadomian orogeny, to a more evolvedand openedbasininfilled bytheMarcory Formation, represents a more evolved and widespread basinwithwiderpotentialsourceareas,developedduring thebreak-upofWestGondwana.
AcompositezircongrainoftheGrandmontsandstone (sampleMN1;ZR49) demonstratesthat crustwithca.
586Maoldrocksbecamerecycledduringmagmatismat ca. 567Ma,andunderlinestheexistenceof twodistinct Ediacaranmagmaticeventsinthesourcearea.
One should expect to identify the Ediacaran River- nous volcanic event as reworked zircon grains in the overlying Cambrian Marcory Fm. However, this is not the case. A rapid burial of the Rivernous volcano sedimentary palaeorelief, related to high rates of sedimentation andavailableaccommodationspacedue to active thermal subsidence, has been proposed for FurongiantoEarlyOrdoviciantimesinWestGondwana (Linnemannetal.,2011;Pereiraetal.,2012)andthelate Neoproterozoic–earlyCambrianintheANS(Avigadand Gvirtzman, 2009) or post-Cadomian rifting extension (Poucletetal.,inpress;VonRaumerandStampfli,2008), whichshouldprecludereworkingoftheRivernousfrom distal(northern)toproximalareas(southernMontagne Noire).
6. Conclusions
TheEdiacaran–Cambrianboundaryhasbeenconfident- lyidentifiedwithinerror,basedonU–Pbzircondating,into theRivernousFm.of thenorthernMontagneNoire. The Rivernous volcanic event is indicated to be the lateral equivalentoftheSe´rie`sTuffoftheAxialZone.Thisfitswell with a latest Ediacaran depositional age (ca. 574Ma) estimatedwithdetritalzirconU–Pbgeochronologyforthe underlyingGrandmontFm.Thelattershouldbeconsid- ered asa time-stratigraphic equivalentoftheacritarch- bearing‘‘SchistX’’Fm.oftheAxialZone(Supplementary data,Fig.S3).
U–PbanalysisofthedetritalzirconsfromtheEdiacaran GrandmontFm.andtheCambrianSeries2MarcoryFm.
suggestsachangeovertimeinthesourcing.TheEdiacaran sedimentsweredepositedinanarrowback-arcbasinfar from the influence of far cratonic sources, whereas CambrianSeries2 detritalsedimentswerederivedfrom maturesourcerocksinvolvingthedenudationofdifferent Gondwanancratons.
Acknowledgements
The authors thank constructive criticism made by O. Blein and B. Laumonier, and foundingfrom theRGF program of the French Geological Survey (BRGM). This paperisacontributiontoprojectCGL2013-48877-Pfrom SpanishMINECO.
AppendixA. Supplementarydata
Supplementarydataassociatedwiththisarticlecanbe found,intheonlineversion,athttp://dx.doi.org/10.1016/j.
crte.2016.11.002.
References
Altumi,M.M.,Elicki,O.,Linnemann,U.,Hofmann,M.,Sagawe,A.,Ga¨rtner, A.,2013.U–PbLA-ICP-MSdetritalzirconagesfromtheCambrianofAl QarqafArch,central-westernLibya:ProvenanceoftheWestGond- wanansandseaatthedawnoftheEarlyPalaeozoic.J.Afr.EarthSci.
79,74–97.
A´lvaro,J.J.,Vizcaı¨no,D.,1999.Biostratigraphicsignificanceandenviron- mentalsettingofthetracefossilPsammichnitesintheLowerCam- brianoftheMontagneNoire(France).Bull.Soc.geol.France170,821–
828.
A´lvaro,J.J.,Courjault-Rade´,P.,Chauvel,J.-J.,Dabard,M.-P.,Debrenne,F., Feist,R.,Pillola,G.L.,Vennin,E.,Vizcaı¨no, D.,1998.Nouveaude´cou- pagestratigraphiquedesse´riescambriennesdesnappesdePardail- hanetduMinervois(versantsuddelaMontagnenoire,France).Geol.
Fr.1998(2),3–12.
A´lvaro,J.J.,Benziane,F.,Thomas,R.,Walsh,G.J.,Yazidi,A.,2014a.Neo- proterozoic–CambrianstratigraphicframeworkoftheAnti-Atlasand Ouzellaghpromontory(HighAtlas),Morocco.J.Afr.EarthSci.98,1–
15.
A´lvaro,J.J.,Baulus,B.,Clausen,S.,Devaere,L.,Imaz,A.G.,Monceret,E., Vizcaı¨no,D.,2014b.SratigraphyoftheCambrian-LowerOrdovician volcanosedimentarycomplexes,northernMontagneNoire,France.
Stratigraphy11,83–96.
Arthaud,F.,1970.E´tudetectoniqueetmicrotectoniquecompare´ededeux domaineshercyniens:lesnappesdelaMontagnenoire(France)et l’anticlinoriumdel’Iglesiente(Sardaigne).PhD,Universite´ deMont- pellier.Pub.USTELA,Montpellier.SerGeol.Struct.1,175p.
Avigad,D.,Gerde,A.,Morag,N.,Bechsta¨dt,T.,2012.CoupledU–Pb–Hfof detritalzirconsofCambriansandstonesfromMoroccoandSardinia:
implicationsforprovenanceandPrecambriancrustalevolutionof NorthAfrica.GondwanaRes.21,690–703.
Avigad,D.,Gvirtzman,Z.,2009.LateNeoproterozoicriseandfallofthe northernArabian–Nubianshield: therole oflithosphericmantle delaminationandsub-sequentthermalsubsidence.Tectonophysics 477,217–228.
Avigad,D.,Kolodner,K.,McWilliams,M.,Persing,H.M.,Weissbrod,T., 2003.OriginofnorthernGondwanaCambriansandstoneasrevealed bySHRIMPdatingofdetritalzircons.Geology31,227–230.
Bard,J.-P.,Loueyit,G.,1978.Surl’originedesgneissoeille´sdel’Espinouse danslazoneaxialedelaMontagnenoire(Massifcentral);conse´- quencestectoniques.Bull.Soc.geol.France20,751–772.
Blein,O.,Baudin,T.,Soulaimani,A.,Cocherie,A.,Che`vremont,P.,Admou, H.,Ouanaimi,H.,Hafid,A.,Razin,P.,Bouadbelli,M.,Roger,J.,2014.
Newgeochemical,geochronologicalandstructuralconstraintsonthe EdiacaranevolutionoftheSouthSirwa,Agadir-MelloulandIguerda inliers,Anti-Atlas,Morocco.J.Afr.EarthSci.98,47–71.
Bowring,S.A.,Schoene,B.,Crowley,J.L.,Ramezani,J.,Conon,D.J.,2006.
High-precision U–Pb zircon geochronology andthe stratigraphic record:progressandpromise.Geochronology:EmergingOpportuni- ties,PaleontologicalSocietyShortCourse.Paleontol.Soc.Pap.11,23–
43.
Brun,J.-P.,VanDenDriessche,J.,1994.Extensionalgneissdomeand detachmentfaultsystems:structureandkinematics.Bull.Soc.geol.
France165,519–530.
Casas,J.M.,Navidad,M.,Castin˜ eiras,P.,Liesa,M.,Aguilar,C.,Carreras,J., Hofmann,M.,Ga¨rtner,A.,Linnemann,U.,2015.TheLateNeoprote- rozoicmagmatismintheEdiacaranseriesoftheEasternPyrenees:
newagesandisotopegeochemistry.Int.J.EarthSci.104,909–925.
Castin˜ eiras,P.,Navidad,M.,Liesa,M.,Carreras,J.,Casas,J.M.,2008.U–Pb zirconages(SHRIMP)forCadomianandLowerOrdovicianmagma- tism in the Eastern Pyrenees:new insights inthe pre-Variscan evolutionofthenorthernGondwanamargin.Tectonophysics461, 228–239.
Charles,N.,Faure,M.,Chen,Y.,2009.TheMontagneNoiremigmatitic dome emplacement(French Massif Central): newinsights from petrofabricandAMSstudies.J.Struct.Geol.31,1423–1440.
Cobbold,E.S.,1935.LowerCambrianfaunasfromHe´rault,France.Ann.
Mag.Nat.Hist.(ser.O)16,25–48.
Cocherie,A.,Baudin,T.,Autran,A.,Guerrot,C.,Fanning,M.,Laumonier,B., 2005.U–Pb zircon(ID-TIMSand SHRIMP)evidencefortheearly Ordovician intrusion of metagranites in the Late Proterozoic
M.Padeletal./C.R.Geosciencexxx(2017)xxx–xxx 9
GModel
CRAS2A-3348;No.ofPages11
CanaveillesGroupofthePyreneesandtheMontagneNoire(France).
Bull.Soc.geol.France176,269–282.
Couzinie´,S., etal.,2017.C.R.Geoscience.349(thisissue).
Demange,M.,1975.StylepenniquedelazoneaxialedelaMontagnenoire entreSaint-PonsetMurat-sur-Ve`bre(Massifcentral).Bull.BRGMI (2),91–139(2ese´rie).
Demange,M.,1982.E´tudege´ologiquedumassifdel’Agout,Montagne noire(PhD,Universite´ Paris-6)..
Demange,M.,1985.Theeclogite-faciesrocksoftheMontagneNoire, France.Chem.Geol.50,173–188.
Demange,M.,1998.Contributionauproble`medelaformationdesdoˆmes delazoneaxialedelaMontagnenoire:analysege´ome´triquedes plissementssuperpose´sdanslesse´riesme´tase´dimentairesdel’enve- loppe.Implicationspourtoutmode`lege´odynamique.Geol.Fr.4,3–
56.
Demange,M.,Gue´range´-Lozes,J.,Gue´range´,B.,1995.Noticeexplicative, Carte ge´ologie France (1/50 000), feuille Lacaune (987). BRGM, Orle´ans(153p.).
Devaere,L.,Clausen,S.,Steiner,M.,A´lvaro,J.J.,Vachard,D.,2013.Chro- nostratigraphicandpalaeogeographicsignificanceofanEarlyCam- brianmicrofaunafromtheHeraultiaLimestone,northernMontagne Noire,France.Palaeont.Electr.16.2.17A,755–768.
Dickinson,W.R.,Gehrels,G.E.,2009.UseofU–Pbagesofdetritalzirconsto infermaximumdepositionalagesofstrata:atestagainstaColorado PlateauMesozoicdatabase.EarthPlanet.Sci.Lett.288,115–125.
Drost,K.,Gerdes,A.,Jeffries,T.,Linnemann,U.,Storey,C.,2011.Prove- nanceofNeoproterozoicandEarlyPaleozoicsilicicasticrocksofthe Tepla-Barrandianunit(BohemianMassif):EvidencefromU–Pbde- tritalzirconages.GondwanaRes.19,213–231.
Ducrot,J.,Lancelot,J.-R.,Reille,J.-L.,1979.DatationenMontagnenoire d’unte´moind’unephasemajeured’amincissementcrustalcaracte´- ristiquedel’Europepre´varisque.Bull.Soc.geol.France21,501–505.
Faure,M.,Cottereau,N.,1988.Donne´escine´matiquessurlamiseenplace dudoˆmemigmatitiquecarbonife`remoyendelazoneaxialedela Montagnenoire(Massifcentral,France).C.R.Acad.Sci.Paris,Ser.II 307,1787–1794.
Faure,G.,Mensing,T.M.,2005. Isotopes: principlesandapplications.
Wiley,Hoboken(897p.).
Fournier-Vinas,C.,Debat,P.,1970.Pre´sencedemicro-organismesdansles terrainsme´tamorphiquespre´cambriens(schistesX)del’Ouestdela Montagnenoire.Bull.Soc.geol.France12,351–355.
Fre´ville,K.,Cenki-Tok,B.,Trap,P.,Rabin,M.,Leyreloup,A.,Re´gnier,J.-L., Whitney,D.L.,2016.Thermalinteractionofmiddleanduppercrust duringgneissdomeformation:examplefromtheMontagneNoire (FrenchMassifCentral).J.Metamorph.Geol.34,447–462.
Gebauer,D.,Gru¨nenfelder,M.,1977.U–Pbsystematicsofdetritalzircons fromsomeunmetamorphosedtoslightlymetamorphosedsediments ofcentralEurope.Contrib.Mineral.Petrol.65,29–37.
Gebauer,D.,Williams,I.S.,Compston,W.,Gru¨nenfelder,M.,1989.The developmentoftheCentralEuropeanContinental crustsince the EarlyArchaeanbasedonconventionalandion-microprobedatingof upto3.84b.y.olddetritalzircons.Tectonophysics157,81–96.
Geyer,G.,1992.Are-evaluationofBlayacinaCobbold,1932andThora- laspisHupe´,1953(Trilobita:Redlichiida).Paleont.Z.66,99–113.
Ge`ze,B.,1949.E´tudege´ologiquedelaMontagnenoireetdesCe´vennes me´ridionales.Mem.Soc.geol.France62,1–215.
Gradstein,F.M.,Ogg,J.G.,Schmitz,M.D.,Ogg,G.M.(Eds.),2012. The geologicaltimescale2012,Elsevier,Amsterdam(2vols,1144p.).
Gutie´rrez-Alonso,G.,Ferna´ndez-Sua´rez,J.,Jeffries,T.E.,2004.Ageand settingoftheUpperNeoproterozoicNarceaAntiformvolcanicrocks (NWIberia).Geogaceta35,78–82.
Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004. The applicationoflaser-ablation-inductivelycoupledplasma-massspec- trometryto insituU–Pbzircon geochronology.Chem.Geol.211, 47–69.
Kydonakis,K.,Kostopoulos,D.,Poujol,M.,Brun,J.-P.,Papanikolaou,D., Paquette,J.-L.,2014.ThedispersaloftheGondwanaSuper-fanSystem inthe easternMediterranean: newinsights from detritalzircon geochronology.GondwanaRes.25,1230–1241.
Lescuyer,J.-L.,Cocherie,A.,1992.Datationsurmonozirconsdesmeta- dacitesdeSe´rie`s.Argumentspourunaˆgeprote´rozoı¨que terminaldes
«schistesX»delaMontagnenoire(Massifcentralfranc¸ais).C.R.Acad.
Sci.Paris,Ser.II314,1071–1077.
Linnemann,U.,Gerdes,A.,Drost,K.,Buschmann,B.,2007.Thecontinuum betweenCadomianOrogenesis andopening oftheRheic Ocean:
constraintsfrom LA-ICP-MSU–Pb zircon dating and analysis of plate-tectonicsetting(Saxo-ThuringianZone,NEBohemianmassif, Germany).TheEvolutionoftheRheicOcean:fromAvalonian-Cado- mianactivemargintoAlleghenian-Variscancollision.Geol.Soc.Am.
Bull.423,61–96.
Linnemann,U.,Pereira,F.,Jeffries,T.E.,Drost,K.,Gerdes,A.,2008.The CadomianOrogenyandtheopeningoftheRheicOcean:thediacrony of geotectonic processes constrained by LA-ICP-MSU–Pb zircon dating(Ossa-MorenaandSaxo-ThuringianZones,IberianandBohe- mianMassifs).Tectonophysics461,21–43.
Linnemann,U.,Ouzegane,K.,Drareni,A.,Hofmann,M.,Becker,S.,Ga¨rtner, A.,Sagawe,A.,2011.SandsofWestGondwana:anarchiveofsecular magmatismandplateinteractions—acasestudyfromtheCambro- OrdoviciansectionoftheTassiliOuanAhaggar(AlgerianSahara) usingU–PbLA-ICP-MSdetritalzirconages.Lithos123,188–203.
Ludwig,K.R.,2012.UsersManualforIsoplot/Exrev.3.75.BerkeleyGeo- chronologyCenter.Spec.Publ.5,1–75.
Ludwig,K.R.,Mundil,R.,2002.ExtractingreliableU–Pbagesanderrors fromcomplexpopulationsofzirconsfromPhanerozoictuffs.Geo- chim.Cosmochim.Acta66,A463.
Manzotti,P.,Poujol,M.,Balle`vre,M.,2015.Detritalzirconinblueschist- faciesmetaconglomerates:implicationsfortheEarlyPermianpalaeo- topographyoftheWesternAlps.Int.J.EarthSci.104,703–731.
Margalef, A., Castin˜ eiras, P., Casas,J.M., Navidad, M.,Montserrat,L., Linnemann,U.,Hofmann,M.,Ga¨rtner,A.,2017.Detritalzirconsfrom theOrdovicianrocksofthePyrenees:geochronologicalconstraints and provenance. Tectonophysics, http://dx.doi.org/10.1016/
j.tecto.2016.03.015(inpress).
Mattauer,M.,Laurent,P.,Matte,P.,1996.PlissementHercyniensynschis- teuxpostnappeete´tirementsubhorizontaldansleversantsuddela Montagnenoire(sudduMassifcentral,France).C.R.Acad.Sci.Paris Ser.IIa322,309–315.
Meinhold, G.,Morton,A.C.,Avigad,D.,2013. Newinsightsintoperi- Gondwana paleogeography andthe Gondwana super-fan system fromdetritalzirconU–Pbages.GondwanaRes.23,661–665.
Meinhold,G.,Morton,A.C.,Fanning,C.M.,Frei,D.,Howard,J.P.,Phillips, R.J.,Strogen,D.,Whitham,A.G.,2011.Evidencefromdetritalzircons forrecyclingofMesoproterozoicandNeoproterozoiccrustrecorded inPaleozoicandMesozoicsandstonesofsouthernLibya.EarthPlanet.
Sci.Lett.312,164–175.
Melleton,J.,Cocherie,A.,Faure,M.,Rossi,P.,2010.Precambrianprotoliths andEarlyPaleozoicmagmatismintheMassifCentral:U–Pbdataand theNorthGondwanaconnectionintheWestEuropeanVariscanBelt.
GondwanaRes.17,13–25.
Mezger,J.E.,Gerdes,A.,2016.EarlyVariscan(Visean)granitesintthecore ofcentralPyreneangneissdomes:implicationsfromlaserablationU–
PbandTh-Pbstudies.GondwanaRes.29,181–198.
Pereira, M.F., Chichorro, M., Sola´, A.R.,Silva, J.B.,Sa´nchez-Garcı´a, T., Bellido,F.,2011.TracingtheCadomianmagmatismwithdetrital/
inheritedzirconagesbyin-situU–PbSHRIMPgeochronology(Ossa- MorenaZone,SWIberianMassif).Lithos123,204–217.
Pereira,M.F.,Sola´,A.R.,Chichorro,M.,Lope,L.,Gerdes,A.,Silva,J.B.,2012.
North-Gondwana assembly, break-up andpaleogeography: U–Pb isotope evidencefrom detrital andigneouszircons ofEdiacaran andCambrianrocksofSWIberia.GondwanaRes.22,866–881.
Pitra,P.,Poujol,M.,VanDenDriessche,J.,Poilvet,J.-C.,Paquette,J.-L., 2012.EarlyPermianextensionalshearingofanOrdoviciangranite:
theSaint-Eutrope‘‘C/S-like’’orthogneiss(MontagneNoire,French MassifCentral).C.R.Geoscience344,377–384.
Pouclet, A., A´lvaro, J.J., Bardintzeff, J.-M., Gil Imaz,A., Monceret, E., Vizcaı¨no, D., 2017. Cambrian–Early Ordovician volcanism across theSouthArmoricanandOccitanDomainsoftheVariscanBeltin France:continentalbreak-upandriftingofthenorthernGondwana margin.Geosci.Frontiers,http://dx.doi.org/10.1016/j.gsf.2016.03.002 (inpress).
Poujol,M.,Pitra,P.,VanDenDriessche,J.,Ruffet,G.,Paquette,J.-L.,Poilvet, J.-C.,2017.Two-stagepartialmeltingduringtheVariscanextensional tectonics(MontagneNoire,France).Int.J.EarthSci.,http://dx.doi.org/
10.1007/s00531-016-1369-1(inpress).
Raumer(von),J.F.,Stampfli,G.M.,2008.ThebirthoftheRheicOcean— EarlyPalaeozoicsubsidencepatternsandsubsequenttectonicplate scenarios.Tectonophysics461,9–20.
Roger, F.,Respault, J.-P., Brunel,M., Matte, P., Paquette, J.-L., 2004.
Premie`redatationU–Pbdesorthogneissœille´sdelazoneaxialede laMontagnenoire(SudduMassifcentral):nouveauxte´moinsdu magmatismeordoviciendanslachaıˆnevarisque.C.R.Geoscience336, 19–28.
Rubio-Ordo´n˜ ez,A.,Gutie´rrez-Alonso,G.,Valverde-Vaquero,P.,Cuesta,A., Gallastegui,G.,Gerdes,A.,Ca´rdenes,V.,2015.Arc-relatedEdiacaran magmatismalongthenorthernmarginofGondwana:geochronology andisotopicgeochemistryfromnorthernIberia.GondwanaRes.27, 216–227.
Sambridge,M.S.,Compston,W.,1994.Mixturemodellingofmulti-com- ponentdatasetswithapplicationtoion-probezirconages.Earth Planet.Sci.Lett.128,373–390.
Sla´ma,J.,Kosˇler,J.,2012.Effectsofsamplingandmineralseparationon accuracyofdetritalzirconstudies.Geochem.Geophys.Geosyst.13, 1–17.
Sla´ma,J.,Kosˇler,J.,Condon,D.J.,Crowley,J.L.,Gerdes,A.,Hanchar,J.M., Horstwood,M.S.A.,Morris,G.A.,Nasdala,L.,Norberg,N.,Schaltegger, U., Schoene, B.,Tubrett, M.N., Whitehouse,M.J., 2008. Plesˇovice zircon—anewnaturalreferencematerialforU–PbandHfisotopic microanalysis.Chem.Geol.249,1–35.
Soula,J.-C.,Debat,P.,Brusset,S.,Bessie`re,G.,Christophoul,F.,Deramond, J.,2001.Thrust-related,diapiricandextensionaldominginafrontal orogenicwedge:exampleoftheMontagneNoire,southernFrench Hercynianbelt.J.Struct.Geol.23,1677–1699.
Squire, R.J., Campbell,I.H.,Allen, C.M., Wilson, C.J.L., 2006. Did the TransgondwanaSupermontintriggertheexplosiveradiationofani- malsonEarth? EarthPlanet.Sci.Lett.250,116–133.
Tack,L.,Wingate,M.T.D.,DeWaele,B.,Meert,J.,Belousova,E.,Griffin,B., Tahon,A., Fernandez-Alonso, M.A.,2010. The1375 Ma ‘‘Kibaran event’’incentralAfrica:prominentemplacementofbimodalmag- matismunderextensionalregime.Precambr.Res.180,63–84.
Tack,L.,Wingate,M.T.D.,Lie´geois,J.P.,Ferna´ndez-Alonso,M.,Deblond,A., 2001.AnEarlyNeoproterozoicmagmatism(1000–1910Ma)ofthe
Zadinian andMayumbian Groups(Bas-Congo): onset of Rodinia rifting atthewestern edgeofthe Congocraton.Precambr. Res.
110,277–306.
Talavera, C.,Montero, P., Martı´nez Poyatos, D., Williams, I.S., 2012.
EdiacarantoLowerOrdovicianageforrocksascribedtotheSchist- GraywackeComplex(IberianMassif,Spain):evidencefromdetrital zirconSHRIMPU–Pbgeochronology.GondwanaRes.22,928–942.
VanAchterbergh,E.,Ryan,C.G.,Jackson,S.E.,Griffin,W.L.,2001.Data reductionsoftwareforLA-ICP-MS:appendix.In:Sylvester,P.J.(Ed.), LaserAblation-ICP-massspectrometryintheEarthSciences:princi- plesandapplications.MACShortCoursesSeries,Ottawa,Ontario, Canada, pp.239–243.
VanDenDriessche,J.,Brun,J.-P.,1992.TectonicevolutionoftheMonta- gneNoire(FrenchMassifCentral):amodelofextensionaldome.
Geodin.Acta5,85–99.
Vermeesch,P.,2004.Howmanygrainsareneeded foraprovenance study? EarthPlanet.Sci.Lett.224,351–441.
Williams,I.S.,Fiannacca,P.,Cirrincione,R.,Pezzino,A.,2012.Peri-Gond- wananoriginandearlygeodynamichistoryofNESicily:azircontale fromthebasementofthePeloritaniMountains.GondwanaRes.22, 855–865.
M.Padeletal./C.R.Geosciencexxx(2017)xxx–xxx 11
GModel
CRAS2A-3348;No.ofPages11
