TurkishJournalofEarthSciences (TurkishJ.EarthSci.),Vol.14, 2005,pp.185–207. Copyright©TÜB‹TAK PetrographyandPetrologyoftheCalc-AlkalineSar›han Granitoid(NETurkey):AnExampleofMagma MinglingandMixing ZAFERASLAN KaradenizTeknikÜniversitesi,GümüflhaneMühendislikFakültesi,JeolojiMühendisli¤iBölümü, Ba¤larbafl›,TR–29000Gümüflhane,Turkey(E-mail:[email protected]) Abstract: Therearemanyacidicintrusionsofvaryingageinthenorthernandsouthernzonesoftheeastern Pontides,NETurkey,andtheSar›hanGranitoidisoneofthese.TheMaastrichtianSar›hanGranitoidwasemplaced intothepre-Permo–CarboniferousPulurMassif,generallycomprisingmedium-grademetamorphicrocks;the LiassicHamurkesenFormation,thatbeginswiththeDikmetaflconglomerateandcontinuesupwardintovolcano- sedimentaryrocks;andtheMalm–LowerCretaceousHozbirikyaylaFormation,comprisinglimestoneandsandy limestones.TheSar›hanGranitoidcropsoutinanareaofapproximately40km 2,hasanellipsoidalshape,and comprisesmainlyquartzmonzodiorite,granodioriteandlesserquartzdiorite.Theplutoncontainsvolcanicand silicifiedlimestonexenolithsanddioriticmaficmicrogranularenclaves.Theplutonicrocksshowmedium-grained, poikilitic,monzonitic,anti-rapakiviandsometimesmyrmekitictextures,andcontain43–64%plagioclase,6–18% orthoclase,10–29%quartz,5–20%hornblende,1–85%biotite,1–6%opaqueoxides,accessoryamountsof apatite,titaniteandzircon,andsecondaryphasesofcalcite,chloriteandsericite.Sometexturesmaysuggest magmamixing,whereasthepresenceofmaficmicrogranularenclavesindicatesthatmagma-minglingprocesses wereoperativeintheevolutionofthepluton.Theplutonhas65–67%SiO2,1.4–3.1%MgO,4.1–5.5%Na2Oand <1K2O/Na2O.Generally,theplutonisI-type,metaluminousandhascharacteristicsofcafemic-groupgranitoids, suggestingahybridsourcederivedbymixingofsialicandmantlesources.Theplutonhascalc-alkalinecomposition andischaracterisedbyacalc-alkalinegranodiorite-seriestrend.TiO 2,Al2O3,FeO,Fe2O3,MnO,MgO,CaO,P 2O5, BaandNidecreasewhereasNa 2O,K 2O,RbandNbincreasewithincreasingSiO 2 content.Thesegeochemical variationsindicatetheimportanceoffractionalcrystallisation,whichwasmainlycontrolledbyplagioclaseand hornblende.However,someirregularvariationsinmajorandtraceelementsmayberesultsofmagmamixing.Zn, Rb,Sr,La,Pb,ThandZrshowenrichmentwhereasCe,CrandNiexhibitdepletioncomparedtocontinentalcrust values,resemblingthoseofvolcanic-arcgranitoids.Withregardtodiscriminationoftectonicsetting,thepluton representspre-platecollisionvolcanic-arcgranitoids.The 87Sr/86Srratio(0.70504)oftheplutonalsoindicatesa hybridmagmawhichlikelywasderivedbymixingofamantlesourcewithacrustalcomponent.Fieldobservations suggestastopingtypeofascentandemplacementstyle. KeyWords: easternPontides,Sar›hanGranitoid,maficmicrogranularenclaves,magmamixing/mingling,Rb/Sr isotope,petrology,calc-alkalinevolcanic-arcgranite Kalk-AlkalinSar›hanGranitoyidi’nin(KDTürkiye)PetrografisivePetrolojisi: MagmaKar›fl›m›naBirÖrnek Özet: Do¤uPontidler(KDTürkiye)kuzeyvegüneykufla¤›ndade¤iflikyafllardapekçokasidiksokulummevcuttur. Sar›hanGranitoyidibunlardanbiridir.Do¤uPontidgüneykufla¤›ndabulunanMaastrihtiyenyafll›Sar›han Granitoyidi,genellikleortaderecelimetamorfikkayaçlardanoluflanPermo–Karboniferöncesiyafll›PulurMasifi’ni, Dikmetaflkonglomeraüyesiilebafllay›pvolkano-sedimanterkayaçlarladevamedenLiyasyafll›Hamurkesen Formasyonu’nuvekireçtafl›-kumlukireçtafl›ndanoluflanMalm–GeçKretaseyafll›HozbirikyaylaFormasyonu’nu keserekyerleflmifltir.Arazigözlemlerinegöreyükselim-yerleflimmodeli‘ stoping’tipindeolanveyaklafl›k40km 2 biralandaellipsoidalflekildeizlenenSar›hanGranitoyidigenelliklekuvars-monzodiyorit,granodiyoritvekuvars- diyorittenoluflmaktad›r.Sokulum,volkanikvesilisleflmiflkireçtafl›ksenolitleriilediyoritikmafikmikrogranülar anklavlariçermektedir.Ortataneli,poikilitik,monzonitik,anti-rapakivivebazendemirmekitikdokugösterenkalk- alkalinbileflimindekipluton,%43–64plajiyoklas,%6–18ortoklas,%10–29kuvars,%5–20hornblend,%1–8 biyotit,%1–6opakmineralileapatit,titanitvezirkongibitaliminerallervekalsit,kloritveserisitgibiikincil mineralleriçermektedir.Sokulumdatespitedilenbaz›dokular›nbulunmas›magmakar›flmas›na(mixing), 185 ANEXAMPLEOFMAGMAMINGLINGANDMIXING anklavlar›nbulunmas›damagmakar›flmas›na(mingling)iflaretetmektedir.Sokulum%65–67SiO 2,%1.4–3.1 MgO,%4.1–5.5Na2Ove<1K2O/Na2Ode¤erlerinesahiptir.Itipivemetalüminözelli¤indekipluton,kafemikgrup granitlerinözelli¤iniolan,sialikvemantokökenlikaynaklar›nkar›fl›m›ndantüreyenmelezkaynaközelli¤i sunmaktad›r.Kalk-alkalinbileflimindekiplutonkalk-alkalingranodiyoritserilerinyönelimlerinekarfl›l›kgelmektedir. Harkerdiyagram›ndakiSiO2‘yekarfl›TiO2,Al2O3,FeO,Fe2O3,MnO,MgO,CaO,P2O5,BaveNide¤erleriazal›rken Na2O,K2O,RbveNbde¤erlerininartmas›,plajiyoklasvehornblendtaraf›ndankontroledilenkesri(fraksiyonel) kristallenmeyiiflaretetmektedir.Bununlabirlikteanaveizelementlerdekidüzensizde¤iflimlermagma kirlenmesindenkaynaklanabilir.K›tasalkabu¤agörenormalizeedilenizelementlerdenZn,Rb,Sr,La,Pb,ThveZr de¤erlerizenginleflirkenCe,CrveNide¤erlerindebirazalmasözkonusuolupvolkanikyaygranitlerininözelliklerini göstermektedir.Tektonikolarakpluton,volkanikyaygranitlerininözelli¤inisunmaktad›r. 87Sr/86Sroran›n›n 0.70504olmas›magmakökenlikaynakilekabu¤unkar›fl›m›ndanoluflanmelezmagmakökenineiflaretetmektedir. AnahtarSözcükler: Do¤uPontidler,Sar›hanGranitoyidi,mafikmikrogranüleranklav,magmakar›fl›m›,Rb/Sr izotop,petroloji,kalk-alkalinvolkanikyaygraniti Introduction bysedimentaryandmetamorphicrocks(Figure2) Turkeyisdividedintothreemajortectonicregions:the (Adamia etal. 1977).Therocksofnorthernzoneare Taurides,AnatolidesandPontides(Figure1;Ketin youngerthanthoseofsouthernzone(Keskin etal. 1966).TheeasternPontides,risingsteeplyfromthe 1989).ThevolcanicrocksoftheeasternPontideslie BlackSeacoastinlandtoabout200kmsouth,formthe unconformablyonaheterogeneousPalaeozoiccrystalline northernmarginofAnatolia.TheeasternPontideterrane basementcalledthePulurMassif,consistingof isanexampleofpalaeo-islandarcgenerationandlong- metamorphicsequencesofvaryingmetamorphicgrades, termcrustalevolutionfrompre-subductionrifting, andarecross-cutbygranitoidsofPermianage(Y›lmaz througharcvolcanismandplutonism,topost-subduction 1972;Ço¤ulu1975;Gediko¤lu1978;Topuz2000).The alkalinevolcanism(e.g.,Ak›n1978;fiengör&Y›lmaz UpperPalaeozoicsequencehasbeenstudiedbyseveral 1981;Ak›nc›1984).TheeasternPontidesaresubdivided workers(e.g.,A¤ar1977;Okay&fiahintürk1997). intonorthernandsouthernzonesinnortheasternTurkey Liassicvolcanicrocks,tholeiiticincharacter,mostlycrop (Gediko¤lu1978).Thesetwozonesexhibitdistinctive outinthesouthernzone,andarecomposedofbasalt features.Thenorthernzoneconsistsofacidicandbasic withminorandesiticandtrachyandesiticlavas(and volcanicrockswhereasthesouthernzoneischaracterised pyroclasticequivalents).Theseareoverlainconformably ‹stanbul BlackSea N NAFS PONTIDES ANATOLIDES EAFS BORDERFOLDS TAURIDES 0 10 Km NAFS:NorthAnatolianFaultSystem AegeanSea EAFS:EastAnatolianFaultSystem MediterraneanSea studyarea Figure1. TectonicmapofTurkey(fromKetin1966). 186 Z.ASLAN BLACK SEA N RÝZE TRABZON Tonya Kürtün Kaçkar Granitoid Torul GÜMÜÞHANE BAYBURT Þiran Kelkit Sarýhan 0 5 10 km Eocene andesite and basalt Palaeocene trachyandesite Eocene Cretaceous- Upper volcanic rocks Palaeocene Cretaceous volcanic and clastic rocks Palaeozoic Jura-Lower andesite-basalt, GRANITOIDES Cretaceous sandstone and limestone suture zone Palaeozoic metamorphic rocks Figure2. GeologicalmapoftheeasternPontides(fromGüven1993). 187 ANEXAMPLEOFMAGMAMINGLINGANDMIXING byDogger–Malm–Cretaceouspelagiccarbonates.The fiahintürk1997;Y›lmaz etal. 1997;Karsl›etal. 2004). UpperCretaceousseriesunconformablyoverliethese TheMiddleCarboniferousSarayc›kGranodiorite,which carbonaterocks,andisdominatedbysedimentaryrocks hasthecharacteristicsofcalc-alkaline,I-type,cafemic- inthesouthernzoneandbyvolcanicrocksinthe groupgranitoids,cutsthePulurMassif.Duetothis northernpartoftheeasternPontides(Bektafl etal. intrusion,epidotehornfelsandaskarnzonecontaining 1987). magnetiteandhematiteformedlocallyatthecontactwith TheeasternPontidesarealsocharacterisedby countryrocks.TheLiassicHamurkesenFormation,which widespreadacidicintrusionsofvaryingageinboththe unconformablyoverliesthemassif,beginswiththe northernandsouthernzones.Theseintrusionswere Dikmetaflconglomerateandcontinuesupwardwith emplacedinthePalaeozoic,CretaceousandEocenetime volcano-sedimentaryrocks(andesite,basalt,sandstone, intervals,andallhavethegeneralcharacteristicsofcalc- limestone,andcrystal-vitrictuff),allofwhicharecutby alkalinearcgranites(fien&Kaygusuz1998;Aslan& diabasedykes.TheMalm–LowerCretaceous Aslaner1998).Intheregion,magmashadarangeof HozbirikyaylaFormationconformablyoverliesthe agesandcomposition,probablyreflectingemplacement HamurkesenFormationandcompriseslimestoneand intovariablegeodynamicenvironments(Ço¤ulu1975; sandylimestone.TheHozbirikyaylaFormationis Taner1977;Gediko¤lu1978;Boztu¤etal. 2002,2003; conformablyoverlainbytheOtlukbelimélange, Mooreetal. 1980;Van1990;Okay&fiahintürk1997; comprisingredlimestone,pyroclasticrocks,serpentinite, Y›lmazetal. 1997;Aslan&Aslaner1998).Whole-rock radiolarite,limestoneolistolithsandbrecciatedbasalt. compositionsrangefromlow-Ktholeiiticthroughcalc- TheMaastrichtianSar›hanGranitoidcutsallofthese alkalinemetaluminousgranitoidsandperaluminous lithologies(Figure3).Alluviumistheyoungestrockunit leucogranitestosilica-oversaturatedalkalinesyenitesand inthearea. monzonites(Y›lmaz&Boztu¤1996;Boztu¤2001; Intheregion,thefirstdetailedgeologicalstudywas Boztu¤ etal. 2002,2003).Thegeodynamic madebyA¤ar(1977).Accordingtothisstudy,theageof environmentsofemplacementincludearc-collision,syn- Sar›hanGranitoidisPalaeozoicandofgranodioritic collisionalcrustalthickeningandpost-collisional