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Upper Cretaceous Eclogite-Facies Metamorphic Rocks from the Biga

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Upper Cretaceous Eclogite-Facies Metamorphic Rocks from the Biga TurkishJournalofEarthSciences (TurkishJ.EarthSci.),Vol.9, 2000,pp.47-56. Copyright©TÜB‹TAK UpperCretaceousEclogite-FaciesMetamorphicRocks fromtheBigaPeninsula,NorthwestTurkey ARAL‹.OKAY1 &MUHARREM SATIR2 1‹stanbulTeknikÜniversitesi,AvrasyaYerbilimleriEnstitüsü,Ayaza¤a TR-80626‹stanbul-TURKEY,(e-mail:[email protected]) 2UniversitätTübingen,InstitutfürMineralogie,PetrologieundGeochemie,Wilhelmstrasse 56,D-72074Tübingen-GERMANY,(e-mail:[email protected]) Abstract: Medium-grademetamorphicrockscropoutoveralargeareaundertheNeogenesedimentaryand volcanicrocksinthecentralBigaPeninsulainnorthwestTurkey.TheseÇaml›cametamorphicsconsistdominantly ofquartz-micaschistswithminorcalc-schist,marble,quartziteandmetabasite.Someofthemetabasitesinthe Çaml›cametamorphicspreserveanearlyeclogite-faciesmineralassemblageofgarnet+omphacite+glaucophane +rutile±paragonite,stronglyoverprintedbygreenschist-faciesmineralassemblages.Theconditionsofthe eclogite-faciesmetamorphismhavebeendeterminedas510±50°Ctemperaturesandaminimumpressureof11 kbar,basedonthegarnet-clinopyroxeneFe-Mgpartitioningandthejadeitecontentofomphacite,respectively.The highphengitecontentofthepotassicwhitemicasinthequartz-micaschistsandthecloseinterlayeringofquartz- micaschistsandthemetabasitessuggestthatthewholeoftheÇaml›cametamorphicshasundergoneregional eclogite-faciesmetamorphism.Rb-Srphengiteagesfromthreequartz-micaschistsamplesfromtheÇaml›ca metamorphicsrangefrom65to69MaandindicateaMaastrichtianagefortheeclogite-faciesmetamorphicevent. TheÇaml›cametamorphicsprobablyareapartoftheRhodopemetamorphiccomplex,whichexhibitsasimilar lithostratigraphyandmetamorphichistory. KeyWords: Eclogitefaciesmetamorphism,Rb/Srdata,Turkey,BigaPeninsula,RhodopeMassif BigaYar›madas›’ndaGeçKretase’deEklojitFasiyesinde MetamorfizmaGeçirmiflBirBirim Özet: BigaYar›madas›’n›nmerkezikesimindemetamorfikkayalargeniflbirbölgedemostraverir.Çaml›ca metamorfitleriolarakisimlendirilenbukayalaresasolarakkuvars-mikaflistlerdenyap›lm›flt›r.Kuvars-mikaflistler ileardalanmal›olarakazoranlardakalkflist,mermer,kuvarsitvemetabazitlerdeÇaml›cametamorfitleriiçindeyer al›r.Çaml›cametamorfitleriiçindeyeralanbaz›metabazitlerdegranat+omfasit+glokofan+rutil±paragonit’den oluflaneklojitfasiyesiparajenezlerisaptanm›flt›r.Builkseleklojitmineraltoplulu¤udahasonrageliflenamfibolitve yeflilflistfasiyesimetamorfizmas›sonucubüyükölçüdetahripolmufltur.Granatileomfasitaras›ndakiFe-Mg da¤›l›m›,veomfasitlerdekimaksimumjadeitoran›,eklojitfasiyesimetamorfizmas›s›ras›ndas›cakl›¤›n510±50°C, minimumbas›nc›nise11kbaroldu¤unugösterir.Kuvars-mikaflistlerdekibeyazmikalar›nyüksekfengitiçeri¤i,ve metabazitlerilekuvars-mikaflistlerins›ks›kardalanmal›olarakbulunmalar›,Çaml›cametamorfitlerinintümünün eklojitfasiyesindemetamorfizmageçirdi¤ineiflareteder.Üçkuvars-mikaflistnumunesindeneldeedilenfengitRb- Srizotopikyafllar›65ile69Maaras›nadüfler,veeklojitfasiyesindekimetamorfizman›nMaastrihtiyenyafl›nda oldu¤unugösterir.Çaml›cametamorfitleri,benzerlitolojikvemetamorfiközelliklergösterenRodopmetamorfik kompleksininmuhtemelbirparças›d›r. AnahtarSözcükler:Eklojitfasiyesimetamorfizmas›,Rb/Srverileri,BigaYar›madas›,RodopMasifi 47 ECLOGITEFROMBIGAPENINSULA,NWTURKEY Introduction Okayetal. (1991)groupedthepre-Neogenesequences Inthispaperweprovidenewpetrologicalandisotopic oftheBigaPeninsulaintwotectoniczonesseparatedby dataonalargeareaofmetamorphicrocksfromthe adiscontinuousnortheast-trendingbeltofUpper centralBigaPeninsulainnorthwestTurkey,andshow Cretaceousophioliticmélange.Southeastofthemélange thattheserockshaveunderwenteclogite-facies beltliestheSakaryaZone,whichconsistsoftheKazda¤ metamorphismintheLateCretaceous.TheBiga metamorphiccomplexatthebaseoverlaintectonicallyby Peninsulaischaracterisedbyapoorlyunderstood thePermo-TriassicKarakayaComplex(Figures1&2). complexgeologywithoutcropsofvariousmetamorphic, TheJurassicandLowerCretaceoussedimentaryrockslie magmaticandsedimentaryrocks(Bingöl etal. 1975; unconformablyovertheKarakayaComplex.Thepre- Okay etal. 1991,1996;Pickett&Robertson1996). Neogenerocksnorthwestofthemélangebeltare Figure1. TectonicmapofthenorthernAegeanandtheBalkans.TheoutcropsofmetamorphicrocksoftheRhodope,Serbo-Macedonian andStrandjamassifsareshowninblack.Thicklineswithsolidtrianglesindicatesutureswithoriginalsubductionpolarities,thosewithopen trianglesaremajorintra-continentalthrustsandthatwiththehalf-arrowisatransformfault. 48 A. ‹.OKAY&M.SATIR 02040km Figure2. GeologicalmapoftheBigaPeninsulashowingthetectonicsettingoftheÇaml›cametamorphics. 49 ECLOGITEFROMBIGAPENINSULA,NWTURKEY assignedtotheEzineZone(Okayetal. 1991).Theycrop micaschists.IntheeastaroundthevillageofKayac›k,the outwidelynorthofEzineandwestofKarabiga(Figure Çaml›cametamorphicsaretectonicallyoverlainbysmall 2).Thenorth-tonortheast-trendingOvac›kFaultdivides bodiesofserpentinite(Figure3).Contactrelationsof thepre-NeogenerocksnorthofEzineintwodistinct theseultramaficbodiesillustratethattheemplacementof sequences.WestoftheOvac›kFaultthereisathick theultramaficrockspostdatedtheregional epicontinentalPermo-Carboniferoussequenceregionally metamorphismoftheÇaml›cametamorphics.The metamorphosedatlowgreenschist-faciesconditions.This Çaml›camicaschistsarealsocutbysmallgranitoid Karada¤sequenceismadeupofabasalclasticunitof intrusionsmostprobablyofOligo-Mioceneage. shale,quartzite,andsandstoneoverlainbyneritic TheÇaml›cametamorphicshaveanapparentlysimple limestones,~1600mthick.Theupperpartsofthe internalstructure.Thefoliationsurfacesinthe limestoneseriescontainLatePermianfusulinids micaschistsgenerallytrendnorth-southanddiptothe (Kalafatç›o¤lu1963;Okay etal. 1991).Theneritic westat20°to50°(Figure4).Alargenumberof limestonesareoverlainbyasyn-orogenicclasticseriesof mesoscopicisoclinalfoldswithaxialsurfacesparallelto shale,siltstone,calci-turbidite,pelagicchertylimestone thefoliationoccurinthemicaschists.Themetamorphic andolistolithsoflimestoneandbasalt.Alargeslabof rocksalsocontainanorth-tonorth-northeast-trending ultramaficrocks,theDenizgörenophiolite,tectonically subhorizontalminerallineation,definedlargelyby overliesthesyn-orogenicclasticsequence(Figure3).The elongatedquartzgrains.Theminerallineationis Karada¤sedimentarysequencewasinitiallythoughtto particularlystronginthevicinityoftheOvac›kFaultand signifyalatestPermiantoTriassicophioliteobduction becomesweakereastward. (Okay etal. 1991).However,117±2Ma 40Ar/39Ar TheÇaml›cametamorphicsareseparatedinthewest hornblendeagesfromanamphibolitesliverfromthebase fromtheDenizgörenophiolitebytheOvac›kFault,which oftheDenizgörenophiolitepointtoanEarlyCretaceous formsabroadnorth-tonortheast-trendingarc,33km (Aptian)ratherthanaPermo-Triassicophioliteobduction long.Intheextremenorth,wheretheflyschsequence (Okayetal. 1996). cropsoutundertheDenizgörenOphiolite,theOvac›k EastoftheOvac›kFaultthereisanother FaultformsthetectoniccontactbetweentheÇaml›ca metasedimentarysequence,whichdiffersfromthe metamorphicsandtheflyschsequenceoftheKarada¤ Karada¤sequenceinlithologyandmetamorphicgrade. unit(Figure3).TheOvac›kFaultdipswesttonorthwest TheseÇaml›cametamorphics,whichincludeeclogite withthedipangleincreasingfrom30°inthenorthto lenses,formtheobjectofthispaper. 80°inthesouth.Thesteepdipofthefaultplanenorth ofEzineandtheoutcroppatternoftheNeogene sedimentsintheregionsuggestthatthesouthernpartof TheÇaml›caMetamorphics theOvac›kFaultisrejuvenatedasanormalfaultdefining TheÇaml›cametamorphicscoveranareaof~250km 2 thewesternmarginoftheBayramiçNeogenebasin betweentheOvac›kandKar›ncal›faultsandforma (Figure2).InthevicinityoftheOvac›kFaulttheÇaml›ca westwarddippingstructuralsequenceofoverseven metamorphicshaveastrongprotomyloniticoverprint kilometresinthickness(Figure3).Thetypesectionofthe withathicknessof5-6m.Thelineationandfoliationdata Çaml›cametamorphicsisalongtheroadtothevillageof suggesteitherthattheOvac›kFaultisanorth-south Çaml›ca,whichbranchesofffromtheEzine-Çanakkale directedthrustthathasbeensubsequentlystronglytilted highway.Over80%oftheÇaml›cametamorphicsare westward,orthatitisatranspressionalstrike-slipfault. madeupofgrey,brown,greenishbrown,well-foliated ThepoorlyexposedKar›ncal›Faultformthe quartz-micaschistswiththecommonmineralassemblage southeasternboundaryoftheÇaml›cametamorphics. ofquartz+whitemica+carbonate+albite±chlorite± Kar›ncal›Faultisasteeplydippingnortheast-trending clinozoisite±garnet.Apartfromthesemonotonous faultzonethatjuxtaposestheÇaml›cametamorphicswith quartz-micaschists,thereareyellowishcalc-schists, metashalesandmetasiltstones,whichareassigned white,yellow,blackmarbles,whitequartzites, tentativelytotheNilüferunitoftheKarakayaComplex amphibolitesandalbite-chloriteschists,whichoccuras (Okayetal. 1991).Theselow-grademetamorphicrocks onetotenmetrethickhorizonswithinthequartz- comprisethinsliversofserpentinite. 50 A. ‹.OKAY&M.SATIR + + + + + Figure3. Geologicalmapandcross-sectionoftheregionnorthofEzine.SeeFigure2forlocation. 51 ECLOGITEFROMBIGAPENINSULA,NWTURKEY Figure4. StereographicprojectionsofthefoliationandlineationintheÇaml›cametamorphics.Inthecontouredstereonet,thecontoursareat3,5,7, 9and11% EclogitesintheÇaml›cametamorphics matrix,whicharepartiallyreplacedbyfineintergrowths Thinbandsofamphibolitesarefoundsporadically ofgreencalcicamphiboleandalbite.Inonesample,pale throughouttheÇaml›cametamorphics.However,the apple-greenomphaciteispreservedinthepressure mainoutcropsofmetabasicrocksareabout1.5kmwest shadowsofgarnetporphyroblastsillustratinganearly ofthevillageofÇaml›ca.InthislocalityaroundDedetepe, eclogite-faciesmetamorphism.Theinitialeclogite-facies garnet-bearingmetabasicrocksformseverallarge assemblageappearstohavebeengarnet+omphacite+ massiveoutcropsandshowtexturestypicalof
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