The tectonic setting of volcanic rocks for dahalajunshan formation in wusun mountain region, west tianshan mountain

Dahalajunshan formation volcanic rocks are mainly volcaniclastic rocks of the continental, clipping a small amount of volcanic lava, and transitional land-sea sedimentary environment. Basalt volcanic rocks are alkaline basalt sequence, with low silica, high-Al, Ca, K2O/Na2O ratio and rich iron-magnesium mineral. Mg values of the Basalt are 0.34 ∼ 0.69, averaging 0.53, lower than the primary magmatic but greater than its scope of crustal material. Trace elements is greater than the averaging value of the lower crust but higher than the upper crust. On the whole,the basalt volcanic rocks have the feature of enriching Rb, Th, U, Ta, P, Ti, with the lower content of transition metal elements of Cr, Ni, Co, showing that there had been involved in crustal material during the process of forming magma. The studies have shown that dahala Junshan Formation basaltic magma formed in the intraplate rift environment, maybe related to the slab collapsing of the ancient Tianshan ocean during the early Carboniferous. (authors)