Petrological Characteristics And Tectonic Environment Of The Late Paleozoic Volcanic Rocks In Qinghe Xinjiang

Researched area is located at the south margin of the east section of Altai mountain,the southwest margin of Siberia plate,northeast margin of Junggar plate,where is the oblique collision and jointing position of the two plates.Metabasites of Weidong,Qinghe,Xinjiang is selected as the research object of the study.After detailed wild-field geological survey, key section measuring and indoor microscope study, the wild-field distribution, scale, occurrence and assemblage and petrology of the rocks are ascertained.Meanwhile, the petrogeochemistry analysis and isotopic dating of rock samples were tested. So we can discuss the tectonic environment and formation age of metabasites via geochemistry and isotope geochronology. Main cognitions are acquired as follows:The sedimentary environment of Jiangbasitao formation in Weidong Country should be from deep-sea,sub-deep sea to epeiric sea by analysis of the measured profile.The LA-ICP-MS zircon U-Pb isotope age of metadacite of Jiangbasitao formation in Weidong Country.It shows that the formation age of Jiangbasitao is from late devonian to early carboniferous(D3-C1).The geochemical analysis showed that the metabasites have the characteristics with poor alkali, especially poor potassium and low TiO2.So they should be low potassium tholeiite.The distribution model of rare-earth elements is weak LREE enrichment and high∑REE type.The spiderweb figure of trace elements with MORB standardization shows that large ion lithophile elements (K, Sr, Rb, Ba) are enriched,high field strength elements are lossed and Nb, Ta and Hf with negative anomaly. The geochemical characteristics show that the tectonic environment of metabasites is retroarc basin.Altay region is the trench-arc-basin system evolution stage from Late Devonian to the end of Early Carboniferous.Starting from the Late Devonian,due to Junggar ocean subduction under the northern continent,along Eerqisi-Wulungu lake subduction zone,Kalatongke island arc belt and Ashele-Crane retroarc basin belt are formed.Therefore,the formation environment of research area during the late Devonian-Early Carboniferous and the overall regional tectonic environment should be corresponding.