Geochronology And Geochemistry Features Of Mafic In The Precambrian Strata Of The ASku Area,in The NW Tarim

The Tarim craton is one of the three ancient cratonic craton in China,with a complete Precambrian crystalline basement and a good Neoproterozoic unmetamorphosed sedimentary cover.Based on the basic rocks in the Precambrian strata of the Aksu area,the northwest margin of the Tarim block,this paper determines the formation age depend on the zircon of LA-ICP-MS U-Pb dating,and discusses the source area of the magma and the tectonic undergrand of its formation by the study of the characteristics of the main and trace elements of the basic rocks.Through fi eld investigation in Aksu area and laboratory analysis,we found that there are basic rocks in the Precambrian strata in the Aksu region,it developed a large-scale mafic dyke and the outcrop of the diabase dyke in the Changcheng System-Akesu group and basalt in the Sugetbrak formation.According to the characteristics of microscope and zircon LA-ICP-MS U-Pb dating results,it is shown that the zircon age of the mafic dyke in the southern Aksu group of southern Wushi area is 354±6.8Ma(Early Carboniferous),the zircon age of the diabase vein is 290.5±4.7Ma(Early Permian),it maybe a product of Permian Large Igneous Province in Tarim Basin.The rock classification of the mafic dyke belongs to subalkaline gabbro.The geochemical characteristics are the enrichment of the large ion lithotony element Rb,the loss of high field elements such as Nb,Ta and Th,the magma comes from the interaction of the mantle plume source and the lithosphere mantle,and the tectonic background is the intraplate basalt.The diabase rocks are classified as subalkaline gabbro.The geochemical characteristics are LILE Ba and high field strong elements(HFSE)Nb,Ta and Th,which are relatively loss of large ion litholitic elements K and Sr.The magma may be derived from the enriched mantle and the tectonic background is in the basalt.The basalt of the Sugetbrak formation in the Yuermeinak area has different properties from the basic dyke of the Aksu group in the southern Wushen area.The basalt in Sugetbrak formation is a transitional basalt between the tholeiite and alkaline basalt,the geochemistry is characterized by the obvious enrichment of the Ba and the a sight loss of large ion lithophile element Sr.The magma source area of basalt is probably asthenosphere mantle plume,and the tectonic setting is intraplate rift environment.Based on the previous geochronological data,the age of formation should be around 615Ma,which is a response to Rodinia supercontinent pyrolysis.