www.geologicacarpathica.skGEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA, OCTOBER 2013, 64, 5, 375382 doi: 10.2478/geoca-2013-0025IntroductionProvenancestudiesbasedondatingofdetritalmineralsen-ablestheestablishmentofthesource,especiallywhenthehinterland is distinct in the age of crystalline basement rocks(e.g. Dallmeyer & Takasu 1992; Capuzzo et al. 2003; Hodgesetal.2005;Neubaueretal.2007;vonEynatten&Dunkl2012 for review). Such studies also allow monitoring of tec-tonic processes in the source region as well as their tectono-thermalhistorywhensufficientdataareknownintherespective source regions (Ruhl & Hodges 2005).The results of recent field work and collaborative 40Ar/39ArdatingofdetritalwhitemicafromthesynorogenicUpperCretaceousSinaiaFlyschFormationintheSouthernCar-pathianorogenhaveenabledconclusionsastotheoriginofsedimentsdepositedinthatsynorogenictrench.ThesenewdatademandsignificantrevisionofpreviousinterpretationsofthetectonothermalevolutionoftheSouthernCarpathianorogen, and provide constraints for regional Late Cretaceousgeodynamics.Geological settingThe Southern Carpathian orogen is comprised of a sequenceof metamorphic basement nappe complexes structurally sepa-rated by variably metamorphosed intercalations of Upper Pa-leozoic and Mesozoic cover sequences (e.g. Burchfiel 1976,1980; Krutner et al. 1981, 1988; Sndulescu 1984; KrutnerOrigin of sediments during Cretaceous continentcontinentcollision in the Romanian Southern Carpathians:preliminary constraints from 40Ar/39Ar single-grain datingof detrital white micaFRANZ NEUBAUER and ANA-VOICA BOJARDepartment of Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria;franz.neubauer@sbg.ac.at(Manuscript received January 7, 2013; accepted in revised form June 5, 2013)Abstract: Single grains of detrital white mica from the lowermost Upper Cretaceous Sinaia Flysch have been datedusingthe 40Ar/39Artechnique.TheSinaiaFlyschwasdepositedinatrenchbetweentheDanubianandGeticmicrocontinental pieces after the closure of the Severin oceanic tract. The Danubian basement is largely composed of aPanafrican/Cadomian basement in contrast to the Getic/Supragetic units with a Variscan-aged basement, allowing thedistinction between these two blocks. Dating of detrital mica from the Sinaia Flysch resulted in predominantly Variscanages (3293 and 2884 Ma), which prove the Getic/Supragetic source of the infill of the Sinaia Trench. SubordinateLate Permian (2638 and 25510 Ma), Early Jurassic (1854and 1833 Ma) and Late Jurassic/Early Cretaceous(1493 and 1403Ma) ages as well as a single Cretaceous age (984Ma) are interpreted as representing the exposureof likely retrogressive low-grade metamorphic ductile shear zones of various ages. Ductile shear zones with similar40Ar/39Ar white mica ages are known in the Getic/Supragetic units. The Cretaceous ages also show that Cretaceousmetamorphic units were already subject to erosion during the deposition of the Sinaia Flysch.Key words: provenance study, nappe stacking, retrogressive shear zone, Ar-Ar dating, white mica.1993;Berza&Iancu1994;Iancuetal.2005;Schmidetal.2008;Balintonietal.2010,2011;Balintoni&Balica2012).TheirpalinspasticoriginswerebetweentheEuropeanplate(Moesian promontory) and the Vardar-Mure oceanic domain(awesternextensionoftheTethys)exposedtothewestandnorthofthepresent-daySouthernCarpathians(Fig.1)(e.g.Channel & Kozur 1997).ThetectonostratigraphicsuccessionexposedwithintheSouthernCarpathianorogencomprisesfourmajornappecomplexes(Iancuetal.2005andreferencestherein).Fromstructurallylowertohigherparts,theseinclude(Figs.1,2):(1) The Danubian nappe complex (with Cadomian granitoids,andmedium-grademetamorphicsequenceswithgranulite-likegneisses,orthogneissesandmeta-granitoidsLiegoiset al. 1996; Balintoni et al. 2011; Balintoni & Balica 2012);(2)theJurassic/CretaceousSeverinophiolite-bearingunit;(3) the Getic nappe complex (with mainly Variscan medium-grademetamorphicsequenceswithorthogneiss,paragneissand garnet-micaschist); and (4) the Supragetic nappe complex(mainlyVariscanmedium-grademetamorphicsequences).The Danubian nappe complex is locally structurally separatedfrom the Getic nappe complex by the Severin Nappe that in-cludesJurassicriftandCretaceousdeep-watersedimentarysequences,namelytheso-calledSinaiaFlysch(Burchfiel1976;Sndulescu1984;Iancuetal.2005).Sedimentaryse-quences have been interpreted as records of the Jurassic sepa-rationofanoriginallycombinedDanubian/Geticcontinentalbasementandcompriseseveralfaciesrealms(Fig.2).Thechronology of the assembly of the present nappe architectureUnauthenticatedDownload Date | 8/3/15 1:57 PM376 NEUBAUER and BOJARGEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA, 2013, 64, 5, 375382generally resembles that of Austroalpine units in the EasternAlpsandWesternCarpathians,andresultedfrommid-LateCretaceous nappe assembly (e.g. Burchfiel 1980; Sndulescu1984; Dallmeyer et al. 1996, 1998; Bojar et al. 1998; Neubauer2002).In detail, the Danubian nappe complex comprises severalAlpinenappes(Berzaetal.1994;Iancuetal.2005).Tec-tonically lower nappes consist of Cadomian medium-grademetamorphicsequences(Lainici-PiuGroup)intrudedbydiscordant granitic plutons also of Cadomian age. Structur-allyhigherAlpineDanubiannappesincludetheDrganAmphiboliteGroup,whichisalsointrudedbygranitoids(Berza & Iancu 1994). The Drgan Amphibolite is tectoni-callyjuxtaposedwithOrdoviciantoMississippian,low-grademetasedimentaryunitsalongductileshearzones.Structural relationships within the contrasting upper Danu-biannappeshavebeeninterpretedtoatleastpartiallyrecordaVariscantectonicevolutionbecauseJurassicse-quenceslocallystratigraphicallyoverlieallcrystallinenappeunits(e.g.Iancuetal.2005;Ciulavuetal.2008).ThreecoverdomainsaredistinguishedintheDanubianrealm.Thesearefromwesttoeast:theSvinia-Svinecea,Fig.1. Simplified tectonic map of the Southern Carpathian orogen (modified after Bojar et al. 1998 and mainly based on Berza et al. 1994).b. basin, k. klippe.PresacinaandCerna-Jiudomains.ThePresacinadomainincludesriftvolcanics.PreviousgeochronologicalresultsofmineraldatingreportedfromtheDanubianbasementsequencesincludeLateProterozoicU-Pbzirconagesofaugengneissandgranitoidsrangingfrom811.32.2to5827Ma, and an 825156Ma Sm-Nd whole rock age fortheDrganAmphibolite(Grnenfelderetal.1983;Pave-lescuetal.1983;Liegeoisetal.1996;Balintoni&Balica2012). K-Ar ages reported for whole-rock samples and con-centratesofamphibole,muscoviteandbiotitedisplayarange between ca. 550 and 70Ma (Grnenfelder et al. 1983;Krutner et al. 1988; Ratschbacher et al. 1993; Dallmeyer etal. 1996, 1998; Bojar et al. 1998). Considered together, theavailableradiometricresultshavebeeninterpretedasarecordoftheeffectsofpenetrativeCadomian/Baikalian(latePrecambrian)tectonothermalactivity(e.g.Balintoni&Balica2012),whichhasbeenvariablyandonlylocallyoverprinted by retrogressive Variscan (Late Paleozoic) and/or Alpine tectonothermal events (e.g. Krutner et al. 1988;Bojar et al. 1998; Willingshofer et al. 2001). The exact ageoftheAlpinemetamorphicoverprintisstillunresolved,andisgenerallywithinverylow-gradeconditionstoatUnauthenticatedDownload Date | 8/3/15 1:57 PM377 ORIGIN OF SEDIMENTS DURING CRETACEOUS COLLISION: Ar/Ar DATING OF WHITE MICA (S CARPATHIANS)GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA, 2013, 64, 5,375382mostuppergreenschistfaciesmetamorphicconditions(Iancuetal.2005;Ciulavuetal.2008;Bojaretal.2010).Age data for Alpine metamorphism are scarce (Krutner etal. 1988; Ratschbacher et al. 1993). The 40Ar/39Ar and K-Arages argue for a succession of events starting at ca. 100Mawith ductile shear zone formation and continuing with exten-sionshearzones,whichformedat80Mainnorthernmostareas(Neubaueretal.1997).Theyoungestagesareataround70Ma(Grnenfelderetal.1983;Ratschbacheretal.1993)displayingterminaltectonicevents.Combiningradiometric ages with the stratigraphic ages of sedimentarycoverunits,atwo-stagehistoryofAlpinenappeassemblywas presented (Bojar et al. 1998; Schmid et al. 1998; Iancuet al. 2005).TheSeverinophiolitecomprisesJurassicriftandophiolitesuccessions.TheophioliteisoverlainbytheSinaiaFlyschdisplayingtheoverthrustingbytheGeticNappe.TheSinaiaFlyschrangesinstratigraphyfromLateJurassictoAptian(Pop1996)andcomprisesmainlyturbiditiclimestoneandsandstone beds and marly/shaly interlayers. Bojar et al. (1998)found zircon fission track ages ranging between 22027 and18819Ma in sandstones from the Sinaia Flysch.The Getic Nappe largely comprises Variscan medium-grademetamorphic sequences (locally eclogite-bearing paragneissesandmicaschistsintrudedbypegmatites)andminorgranites(Krutner et al. 1988; Iancu & Mariuntu 1994). Published ra-diometricresultsincludeanupperintercept,11001000MaU-Pbzirconageforgneiss,andalowerintercept310MaU-Pb zircon age for granite (Pavelescu et al. 1983). A discor-dant granite yielded a U-Pb zircon age of ca. 350Ma (Stan etal. 1992). K-Ar ages range between 350 and 70Ma (Grnen-felderetal.1983;Krutneretal.1988;Ratschbacheretal.1993).Conventionalmulti-grain 40Ar/39ArdatingofwhitemicarevealedaVariscanageofthepenetrativeamphibolite-grade metamorphism with white mica ages of ca. 320290Ma(Dallmeyeretal.1996,1998),whichrepresenttheageofcooling through the Ar retention temperature of white mica atca. 425C according to Harrison et al. (2009).TheSuprageticNappeincludesmedium-grademetamor-phic sequences that have been partially retrogressed along dis-tinct,locallypenetrativeductileshearzones.Low-gradesequencesincludefossiliferousCambriantoSilurian,andUpper Devonian to Mississippian successions in north-west-ernsectorsoftheregion(Krutneretal.1988).VastareasFig.2. Simplified stratigraphic sections of individual units exposed within the Danubian and Getic nappe complexes within the SouthernCarpathian orogen (modified after Bojar et al. 1998).UnauthenticatedDownload Date | 8/3/15 1:57 PM378 NEUBAUER and BOJARGEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA, 2013, 64, 5, 375382arecharacterizedbymonotonousmicaschist,plagioclase-richparagneissandaugengneiss.Conventionalmulti-grain40Ar/39ArdatingofwhitemicarevealedtheVariscanageofthepenetrativeamphibolite-grademetamorphismwithwhitemicaagesofca.320290Ma(Dallmeyeretal.1996,1998).Retrogressed ductile shear zones were dated and interpretedasrecordsofaneventatca.200Ma(ca.Triassic/Jurassicboundary(Dallmeyeretal.1998)).Low-grademetamorphicPennsylvaniancoversuccessionsalsoargueforanAlpinemetamorphism dated to ca. 119Ma (Early Cretaceous) (Dall-meyer et al. 1996). Dragusanu & Tanaka (1999) found similarK-Ar mineral ages of 1883 and 1192Ma in the Suprageticdomain in the east.40Ar/39Ar analytical methodsPreparationofthemineralconcentrateswasperformedatthe University of Graz. Preparation for irradiation, 40Ar/39Aranalyses,andagecalculationswerecarriedoutattheARGONAUTLaboratoryoftheGeologyDivisionattheUniversityofSalzburgusingmethodssimilartothosede-scribed in Ilic et al. (2005). Mineral concentrates were packedinaluminium-foilandloadedinquartzvials.ForcalculationoftheJ-values,flux-monitorswereplacedbetweeneach45unknownsamples,whichyieldedadistanceofca.5mmbe-tween adjacent flux-monitors. The sealed quartz vials were ir-radiatedintheMTAKFKIreactor(Debrecen,Hungary)for16 hours. Correction factors for interfering isotopes were cal-culated from 10 analyses of two Ca-glass samples and 22 anal-yses of two pure K-glass samples (Wijbrans et al. 1995), andare: 36Ar/37Ar(Ca)=0.00026025, 39Ar/37Ar(Ca)=0.00065014,and 40Ar/39Ar(K)=0.015466.Variationsinthefluxofneu-tronsweremonitoredwiththeDRA1sanidinestandardforwhicha 40Ar/39Arplateauageof25.030.05Mahasbeenreported(Wijbransetal.1995).Afterirradiationtheminer-als were unpacked from the quartz vials and the aluminium-foilpackets,andhandpickedinto1mmdiameterholeswithin one-way Al-sample holders. 40Ar/39Aranalyseswerecarried out using a UHV Ar-extraction line equipped with acombined MERCHANTEKTM UV/IR laser ablation facility,and a VG-ISOTECHTM NG3600 Mass Spectrometer.Total fusion analyses of single grains were performed usinga defocused (~1.5mm diameter) 25W CO2-IR laser operatingin Tem00 mode at wavelengths between 10.57 and 10.63m.The laser is controlled from a PC, and the position of the laseron the sample is monitored through a double-vacuum windowon the sample chamber via a video camera in the optical axisofthelaserbeamonthecomputerscreen.Gasclean-upwasperformed using one hot and one cold Zr-Al SAES getter. GasadmittanceandpumpingofthemassspectrometerandtheAr-extractionlinearecomputercontrolledusingpneumaticvalves. The NG3600 is a 18cm radius 60 extended geometryinstrument, equipped with a bright Nier-type source operatedat4.5kV.Measurementwasperformedonanaxialelectronmultiplierinstaticmode,peak-jumpingandstabilityofthemagnet are controlled by a Hall-probe. For each increment theintensities of 36Ar, 37Ar, 38Ar, 39Ar, and 40Ar were measured,thebaselinereadingsonmass35.5areautomaticallysub-tracted.Intensitiesofthepeakswereback-extrapolatedover16 measured intensities to the time of gas admittance either byastraightlineoracurvedfit.Intensitieswerecorrectedforsystemblanks,background,post-irradiationdecayof 37Ar,andinterferingisotopes.Isotopicratios,agesanderrorsforindividualstepswerecalculatedfollowingsuggestionsbyMcDougall&Harrison(1999)usingdecayfactorsreportedby Steiger & Jger (1977). Age calculations were carried outusing ISOPLOT/EX (Ludwig 2001).Petrography of investigated samplesTwosamplesfromdifferentlocalitieswereinvestigated(seeFigs.1and2forsamplelocations).Bothsamplesarefrom the Sinaia Formation of the Severin Nappe exposed totheeast(sampleAVB-194)andwest(sampleAVB-195)oftheGeticBahnaklippe.TheareabelongstotheCerna-Ciudomain. According to geological maps, sample AVB-194 isa Turonian to Senonian sandstone of the cover of the Danu-bianUnit(location:N445408,E224109).SampleAVB-195 is likely an Aptian sandstone close to the Severinophiolites (location: N445238, E224156) representingthe cover of the Severin Nappe.Sample AVB-194 is an immature arkose arenite with angu-larclastswithagrainsizerangingfrom0.1to0.5mm.Themain constituents are quartz, K-feldspar, plagioclase and somewhitemica,degradedchloriteandgarnet.K-feldspar(inpartmicrocline)andplagioclase(inpartoligoclaseaccordingtoopticalproperties),arebothonlyslightlysericitizedandto-getherconstituteca.30percent,withaslightdominanceofK-feldspar. White mica is sometimes intergrown with slightlydegradedbiotite.Garnetclastsareoftenchloritized.Lithiccomponentsarerareandasericitechloriteoccursinseveralsigns.Thesubordinatematrixiscomposedoffine-grainedquartz/feldspar, sericite and chlorite.Sample AVB-195 is a carbonate sandstone with a low per-centage of siliciclastic material and calcite cement. The clastsare 0.1 to 0.4mm in size. Among the limestone clasts, micriticclastsaredominant,whilemicrospariteandmonocrystallinecalcite clasts are rather rare. The siliciclastic fraction (