Geochronology, Geochemistry and Geological Significance of the Late Carboniferous Bimodal Volcanic Rocks in the Eastern Junggar

The study region locates in the southwest margin of Central Asian Orogenic belt, which recorded several volcanic events of different tectonic environment. The volcanic rocks from Late Carboniferous Batamayineishan Formation includes the alkaline series and sub-alkaline series, which formed in 320.2±4.2 Ma. They have a SiO₂ interrupt ranging from 56% to 67.5%. The basaltic rocks and the felsic rocks are closely associated. They show a typical characteristic of bimodal volcanic rocks. Their geochemistry and isotope characteristics suggesting that the basaltic rocks come from a depleted mantle source whereas the felsic rocks come from a source due to anatectic melting of the lower crust and show characteristic of A-type granites. The assemblages of volcanic rocks and the geochemical information of volcanic rocks from Batamayineishan Formation indicate they formed in apost-collision environment. Combining the research results ofthis region, the authors consider the Batamayineishan Formation were generated mainly in the end stage of post-collision of Kalamaili orogenic, which began after cessation of collision, and involved extensional detachment of the thickened lithosphere, leading to extension and thinning of the crust.