The East Anatolia-Lesser Caucasus ophiolite:An exceptional case of large-scale obduction,synthesis of data and numerical modelling  

作　　者：Y.Rolland M.Hässig D.Bosch O.Bruguier R.Melis G.Galoyan G.Topuz L.Sahakyan A.Avagyan M.Sosson 

机构地区：[1]Universitéde Nice Sophia Antipolis,UMR Géoazur,CNRS,IRD,Observatoire de la Côte d’Azur,250 Rue Albert Einstein,06560,Sophia Antipolis,France [2]EDYTEM,Universitéde Savoie e CNRS,UMR 5204,Le Bourget du Lac,France [3]Department of Earth Sciences,University of Geneva,Rue des Maraîchers 13,1205 Geneva,Switzerland [4]University Montpellier,Géosciences Montpellier,UMR-CNRS-UM25243,Place Eugene Bataillon,34095 Montpellier,France [5]Institute of Geological Sciences,National Academy of Sciences,24a Baghramyan Avenue,Yerevan 0019,Armenia [6]Istanbul Teknik Universitesi,Avrasya Yer Bilimleri Enstitüsü,34469 Istanbul,Turkey

出　　处：《Geoscience Frontiers》2020年第1期83-108,共26页地学前缘（英文版）

基　　金：supported by the MEBE (Middle East Basin Evolution) and DARIUS programs jointly supported by a consortium including oil companies,UMPC and the INSU,CNRS.G.Topuz acknowledges TüBITAK grant (#114Y226) for support in field works

摘　　要：We present new,geological,metamorphic,geochemical and geochronological data on the East Anatolian-Lesser Caucasus ophiolites.These data are used in combination with a synthesis of previous data and numerical modelling to unravel the tectonic emplacement of ophiolites in this region.All these data allow the reconstruction of a large obducted ophiolite nappe,thrusted for>100 km and up to 250 km on the Anatolian-Armenian block.The ophiolite petrology shows three distinct magmatic series,highlighted by new isotopic and trace element data:(1)The main Early Jurassic Tholeiites(ophiolite s.s.)bear LILEenriched,subduction-modified,MORB chemical composition.Geology and petrology of the Tholeiite series substantiates a slow-spreading oceanic environment in a time spanning from the Late Triassic to the Middle-Late Jurassic.Serpentinites,gabbros and plagiogranites were exhumed by normal faults,and covered by radiolarites,while minor volumes of pillow-lava flows infilled the rift grabens.Tendency towards a subduction-modified geochemical signature suggests emplacement in a marginal basin above a subduction zone.(2)Late Early Cretaceous alkaline lavas conformably emplaced on top of the ophiolite.They have an OIB affinity.These lavas are featured by large pillow lavas interbedded a carbonate matrix.They show evidence for a large-scale OIB plume activity,which occurred prior to ophiolite obduction.(3)Early-Late Cretaceous calc-alkaline lavas and dykes.These magmatic rocks are found on top of the obducted nappe,above the post-obduction erosion level.This series shows similar Sr-Nd isotopic features as the Alkaline series,though having a clear supra-subduction affinity.They are thus interpreted to be the remelting product of a mantle previously contaminated by the OIB plume.Correlation of data from the Lesser Caucasus to western Anatolia shows a progression from back-arc to arc and fore-arc,which highlight a dissymmetry in the obducted oceanic lithosphere from East to West.The metamorphic P-T-t paths of the obduction sole lithologWe present new,geological,metamorphic,geochemical and geochronological data on the East Anatolian-Lesser Caucasus ophiolites.These data are used in combination with a synthesis of previous data and numerical modelling to unravel the tectonic emplacement of ophiolites in this region.All these data allow the reconstruction of a large obducted ophiolite nappe,thrusted for>100 km and up to 250 km on the Anatolian-Armenian block.The ophiolite petrology shows three distinct magmatic series,highlighted by new isotopic and trace element data:(1) The main Early Jurassic Tholeiites(ophiolite s.s.) bear LILEenriched,subduction-modified,MORB chemical composition.Geology and petrology of the Tholeiite series substantiates a slow-spreading oceanic environment in a time spanning from the Late Triassic to the Middle-Late Jurassic.Serpentinites,gabbros and plagiogranites were exhumed by normal faults,and covered by radiolarites,while minor volumes of pillow-lava flows infilled the rift grabens.Tendency towards a subduction-modified geochemical signature suggests emplacement in a marginal basin above a subduction zone.(2) Late Early Cretaceous alkaline lavas conformably emplaced on top of the ophiolite.They have an OIB affinity.These lavas are featured by large pillow lavas interbedded a carbonate matrix.They show evidence for a large-scale OIB plume activity,which occurred prior to ophiolite obduction.(3)Early-Late Cretaceous calc-alkaline lavas and dykes.These magmatic rocks are found on top of the obducted nappe,above the post-obduction erosion level.This series shows similar Sr-Nd isotopic features as the Alkaline series,though having a clear supra-subduction affinity.They are thus interpreted to be the remelting product of a mantle previously contaminated by the OIB plume.Correlation of data from the Lesser Caucasus to western Anatolia shows a progression from back-arc to arc and fore-arc,which highlight a dissymmetry in the obducted oceanic lithosphere from East to West.The metamorphic P-T-t paths of the obduction sole litho

关 键 词：OPHIOLITE OBDUCTION SUBDUCTION NEOTETHYS 

分 类 号：P581[天文地球—岩石学] P548[天文地球—地质学] P597