Volcanic Rocks Assemblage and Eruption Sequence of Dahalajunshan Formation in Wusunshan Region, Western Tianshan

The volcanic rocks of Dahalajunshan Formation are widespread in the Western Tianshan Mountain, which are mainly exposed at north and south edges and inside of Yili Block. On the basis of previous work, the volcanic rocks of Dahalajunshan Formation exposed in Wusunshan region have been taken as studying objects in this paper. By systematically field geology, profile and petrography, the rock association, stratigraphic sequence and its variation have been determined. The volcanic rocks of Dahalajunshan Formation are overall composed of basalt, andesite, dacite, rhyolite and intermediate-acid pyroclastic rock. At the south part of Yili block, the volcanic rocks in Wusunshan-Tasibashan area are mainly andesite (up to 50%), with a similar proportion of basalt, dacite and rhyolite. In the aspects of lava's eruption sequence, the acid magma was firstly erupted in Wusunshan-Tasibashan area, and then basic and acid magma were erupted in turn, which can be divided into 5~7 eruption cycles, with a character of fissure-central eruption.