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Mineralogy and Geochemistry of Melilite Leucitites

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Mineralogy and Geochemistry of Melilite Leucitites TurkishJournalofEarthSciences (TurkishJ.EarthSci.),Vol.12, 2003,pp.215-239. Copyright©TÜB‹TAK MineralogyandGeochemistryofMeliliteLeucitites, Balç›khisar,Afyon(Turkey) CÜNEYTAKAL DokuzEylülÜniversitesi,MühendislikFakültesi,JeolojiMühendisli¤iBölümü,TR-35100Bornova,‹zmir-Turkey (e-mail:[email protected]) Abstract: TheMiddleMioceneAfyonvolcaniccomplexcropsoutinwest-centralAnatoliaandcomprises productsofextensivepotassic-ultrapotassicvolcanicactivitythatintrudeand/orcoverthesedimentaryformations ofthewesternTaurides.Basedontheirstratigraphicsetting,threestagesofpotassicandultrapotassicvolcanism aredistinguishable.Melilite-leucititelavasaretheproductsofthefirststageandfollowedbylamproitesthat representthesecondstageofvolcanism.Theleucititeblock-andfragment-richBalç›khisarvolcaniclasticsuccession overliestheproductsofthefirstandsecondstagevolcanism.Lacustrinesedimentaryrockscovertheproductsof firstandsecondstagevolcanism.LacustrinesedimentaryrocksaregradationallyoverlainbytheToklukvolcano- sedimentarysuccession.Phonotephriticlavadomes,dykes,andflowsrepresentthethirdstageofvolcanicactivity. MeliliteleucititesfromtwooccurrencesintheAfyonvolcanicprovincewerestudied.Themeliliteleucititescrop outassmalllavadomesandspatiallylimitedlavaflows.Themelilite-leucititelavastypicallyhaveporphyritictexture andarecomposedofleucite,nepheline,bariumfeldspar,melilite,diopside,melanite,calcite,apatite,andopaque minerals.Melilitecrystalsarerelativelygehlenite-toakermanite-rich.Thediopsidicclinopyroxenephenocrystsare partiallyand/orcompletelytransformedtomeliliteaggregates. Geochemically,theSiO2 contentofthemeliliteleucititesvariesfrom44%to47%andtheyareultrapotassic withK2Ocontentsof9.5to11.8%andaverageNa 2O/K2Oofabout2.TheAl 2O3 andCaOcontentsarerather high(18%),whereasTiO 2 contentsarelow(1.22%).MeliliteleucititeshavehighlyfractionatedREEand incompatibleelementcompositions.TheBa(8745ppm),Rb(670ppm)andSr(4802ppm)contentsareenriched relativetoprimitivemantleandchondrites.Themeliliteleucititesweregeneratedbypartialmeltingofaprimitive mantlesourceoranenrichedsourcenearasubductionzoneandcollisionprocessesrelatedtoanactiveplate margin. KeyWords: leucite,melilite,leucicite,ultrapotassic,Afyonvolcanicregion,west-centralAnatolia MelilitLösititlerinMineralojisiveJeokimyas›,Balç›khisar,Afyon(Türkiye) Özet: Bat›-OrtaAnadolu’dayüzlekverenveBat›Toroslar’aaitsedimanterformasyonlar›kesenve/veyaörtenOrta Miyosenyafll›Afyonvolkanikkompleksigeniflyay›l›msunanpotasik-ultrapotasikaktiviteninürünlerinden oluflmaktad›r.Stratigrafikkonumlar›nadayal›olarakpotasikveultrapotasikvolkanizman›nüçevresigörülebilir. Melilit-lösititlavlar›ilkevrevolkanikfaaliyetinürünleridir.Lamproitleriseikincievrevolkanikfaaliyetitemsil etmektedirler.Lösititblokveparçalar›ncazenginolanBalç›khisarvolkaniklasitikserisibirincievrevolkanik aktiviteninürünleriniörtmektedir.Birinciveikincievrevolkanizman›nürünlerigölselsedimanterkayalarile örtülmektedir.BugölselsedimanterkayalardereceliolarakToklukvolkano-sedimanterserisitaraf›ndan üstlenmektedir.Fonotefritiklavdomlar›,dayklar›velavakmalar›çal›flmaalan›ndakiüçünçüevrevolkanik faaliyetlerioluflturmaktad›r. Afyonvolkanikkompleksindeyeralanvehacimselolarakküçüklavdomlar›velavakmalar›fleklindeyüzlek verenikimelilitlösetitoluflumuçal›fl›lm›flt›r.Tipikolarakporfiritikdokusunanmelilit-lösititlavlar›lösit,nefelin, baryumfeldspat,melilit,diyopsid,melanit,kalsit,apatitveopakminerallerdenoluflmaktad›r.Melilitkristallerinde genelliklegehlenit-akermanitbileflimibask›nd›r.Diopsidbileflimindekiklinopiroksenfenokristallerik›smenve/veya tamamenmelilittanelerinedönüflmüfltür.Jeokimyasalolarak%9.5–11.8aras›ndakiK 2OveNa 2O/K2Ooran›n›n ortalama2de¤erleriileultrapotasikkarakterdekimelilit-lösititlerinSiO 2 bilefleni%44ile%47aras›ndad›r.Al 2O3 veCaObileflenleri%18de¤erineulafl›rkenortalamaTiO 2 bileflenleri%1.22de¤erindedir.Melilitlösititleryüksek ayr›mlaflmagösterennadirtoprakvedurays›zelementbileflimlerinesahiptirler.Ba(8745ppm),Rb(670ppm)ve Sr(4802ppm)bileflenleriilkselmantovekondritleregörezenginleflmifltir.Melilitlösititler,dalma–batmave çarp›flmasüreçleriningeliflti¤iaktifk›takenar›nayak›nortamdakismiergimeilemeydanagelmiflilkselbireri¤iyin üstkabuktank›smenkirlenmesiileoluflanbirmagman›nürünleridir. AnahtarSözcükler:lösit,melilit,lösitit,ultrapotasik,Afyonvolkanikbölgesi,bat›-ortaAnadolu 215 MELILITELEUCITITESFROM AFYON Introduction (2000)assumedthattheultrapotassicvolcanicrocks Potassiclavashavetraditionallyattractedscientific werederivedfromamantleenrichedincompatible attentionthatisinverselyproportionaltotheir elementsthroughmantlemetasomatism. abundances.Prevalentinterestinpotassicrocksfocuses Keller(1983)suggestedthattheAfyonvolcanicarea ontheirunusualmineralogy,spectacularchemistry, isapartofaNeogenevolcanicbelt,whichfollowsthe mantlesourcecompositions,andtectonicevolutionofthe Tauridefoldchains,relatedtoLateTertiarycollisionand lithospherebeneathpotassiclavafields.Potassium-rich subductionprocessesalongtheCypriot-Taurusarc.Keller volcanicrocksarelimitedvolumetricallybutare &Villari(1972)suggestedthatthemainvolcanicactivity widespreadinseveraltectonicenvironments,suchas intheAfyonprovincedevelopedattheMiocene–Pliocene intraplateriftzonesinupliftareasorbehindconvergent boundary.Inadditiontothesegeodynamic platemarginsand,toalesserextentinoceanicintraplate interpretations,Besang etal. (1977)reported10K/Ar settings.IntheMediterraneanregion,ultrapotassicrocks agesfromhighlypotassicvolcanicrocksofthesouthern formedalongtheAlpinechainduringtheNeogeneto partofAfyonregionthatrangesbetween8.6Maand Quaternaryperiod.Themostwell-known 14.75Ma.TheproductsofthisMiddleMiocenepotassic- potassic–ultrapotassicvolcanicrocksaredistributednear ultrapotassicvolcanicactivityoverlieandintrudethe continentalandconvergentplatemarginsalongtheAlpine sedimentaryformationsinthenortheasternpartof chain,andtheseincludetheCalatravavolcanicprovinceof westernTaurides,includingtheGeyikDa¤Unitandthe centralSpain(Cebria&Lopez-Ruiz1995),theRhönarea Bozk›rUnit(Özgül1984).GeyikDa¤Unitisthe ofGermany(Jung1995),theRomanco-magmaticregion autochthonousunitofthecentralTauridesandconsistsof (Beccaluvaetal. 1991;Peccerillo1992),andtheAeolian platform-typesedimentsstartingwithaLowerPalaeozoic Islands(Clift&Blusztajn1999)inItaly. (CambrianandOrdovician)basementrocks,followedby InTurkey,potassictoultrapotassicvolcanicrocksare Mesozoic–LowerTertiaryrocks,madeuplargelyof locatedintheAfyonvolcanicprovince,theIspartaarea carbonates.TheBozk›rUnitwhich,correspondstothe (Francalancietal. 2000),andtheSivrihisararea(Özgenç Beyflehir-Hoyran-HadimNappesofPoissonetal. (1984), 1993)(Figure1).Therocksuitesfromtheseareasshare comprisesamélangeofpelagicsediment,spilite,diabase manycharacteristicsand,ingeneral,showthat andultramaficblocksofvarioussizesandages;theage petrogenesisofpotassicmagmaisnotasingularevent spanoftheblocksisbetweenLateTriassicandLate butmustberelatedtoanoverallorgeneralprocessor Cretaceous.TheBozk›rUnittectonicallyoverliesthe processes.Theoccurrenceofpotassium-richvolcanic LutetianflyschoftheGeyikDa¤Unitasaresultoflater rocksintheAfyonvolcanicprovince(Turkey)hasbeen Eocenemovements(Özgül1984).Detailedinvestigation knownsincetheearly1970s(Keller&Villari1972),but andmappingofthesedimentarybasementrocks,ranging inspiteofextensivestudiesbyseveralresearchers,there inagefromTriassictoTertiary,wassetforthbyÖztürk havebeennorecentmineralogicalandstratigraphic &Öztürk(1989).Thatstudyshowedthatthe examinationsoftheseparticularrocks. northeasternmostpartofthewesternTauridesconsists ofanumberoftectonostratigraphicrockgroupswith Basedongeochemicaldatafromdifferentlocalitiesin distinctivestratigraphicalandstructuralfeatures.Asseen theK›rka-Afyon-Ispartavolcanicareas,Francalanci etal. fromthegeologicalmap,theBalç›khisarGroupandthe (1990,2000)andSavaflç›n etal. (1995)indicatedthat Çölovas›allochthonousunits,whichrepresentthe therocksfromtheK›rka-Afyonareahaveanorogenic basementrocksofthestudyarea,weremappedandthen affinity,whereasthosefromtheIspartaareaexhibit comparedandcorrelatedwiththeclassificationofÖztürk orogenicandwithin-plateaffinities.Theultrapotassic &Öztürk(1989).Eachgroupwassimplifiedcomparedto suiteisaproductofaresidual,lithosphericmantle thoseofÖztürk&Öztürk(1989). probablymetasomatisedbyfluidsand/ormeltsof differentorigin(subduction-relatedforK›rka-Afyon Thepurposeofthispaperistopresentwhole-rock rocks;deepasthenosphericoriginforIspartarocks).A major,traceandrare-earthelementchemistryofthe morefertileandprobablydeepermantle,enrichedby potassicsuiteandthemineralchemistriesofthemelilite subduction-relatedcomponents,wasthesourceofthe leucitites,todeterminatetheirgeochemicalaffinities potassicrocks.Aydar etal. (1996)andÇoban etal. relativetoprobablesourcesandtectonicsetting. 216 C.AKAL GeologicalSetting linebetweenAfyontoIsparta,namedtheAntalyafault RegionalTectonics zone.Alongthefaultzone,silica-saturatedtostrongly silica-undersaturatedK-richvolcanicrocksand ThenorthwardsubductionoftheAfricanPlateunder ultrapotassicrockserupted(Savaflç›n etal. 1995; EurasiaPlateresultedinanimportantcontinental Francalancietal. 2000). collisionthatoccurredduringtheMiddle–LateMiocene (Fytikasetal. 1984).Thiscollisionalphasewasfollowed byanextensionaltectonicregime(Koçyi¤it1984; FieldDescription Savaflç›n1990;Savaflç›n&Güleç1990).Thearealocated Thestudyareaislocatedinthesouthernmostpartofthe betweentheeasternpartofwesternAnatoliaandthe Afyonvolcanicprovince(Figure2),~6-kmsouthwestof westernpartofcentralAnatoliaisdominatedbycomplex thetownofBalç›khisar.Thestratigraphicframeworkof structuralelements(Figure2).Koçyi¤it(1984)indicated thestudyisrepresentedby(1)melilite-leucititelavas:
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