东昆仑东段沟里地区洪水川组火山岩夹层锆石U-Pb年代学、岩石成因及对古特提斯洋演化的制约OA

The East Kunlun Orogenic Belt is an important part of the Paleo-Tethys domain,and there are still disagreements regarding the closure time limit of the Paleo-Tethys Ocean in this area.Volcanic rock interlayers in the Hongshuichuan Formation in the Gouli area of the eastern segment of this region were selected for zircon U-Pb isotopic age and petrogeochemical studies.The results show that this suite of volcanic rocks is composed of basaltic andesite,dacite,and rhyolite.The selected zircons in the dacite and rhyolite samples all exhibit mag-matic rhythmic zoning,and most of them have a high Th/U ratio,indicating that they are of magmatic origin.The LA-ICP-MS zircon U-Pb ages are(250±2.1)Ma(MSWD=4.9)and(248±4.5)Ma(MSWD=1.2),represent-ing that the volcanic rocks were formed during the Olenekian period of the Early Triassic.Petrogeochemical analysis shows that this suite of volcanic rock interlayers belongs to the calc-alkaline series,showing the charac-teristics of enrichment in large ion lithophile elements(LILE)such as Rb,Ba,Th,and U,depletion in high field strength elements(HFSE)such as Nb,Ta,P,and Ti,and no obvious anomalies in Zr and Hf,exhibiting the char-acteristics of arc magmatic rocks related to the subduction zone.The basaltic andesite is a magma from the man-tle source area metasomatized by subduction fluids,formed through later crystallization differentiation and crustal material contamination;the dacite and rhyolite have a homologous evolutionary relationship and are products of crustal melting induced by the upwelling of mantle-derived magma,formed in the environment of northward subduction of the Paleo-Tethys Ocean.The study on the age and sedimentary environment of the vol-canic rock interlayers in the Hongshuichuan Formation limits that the closure time of the Paleo-Tethys Ocean in the East Kunlun area is not earlier than 248 Ma.