Geochemistry, zircon U-Pb ages and tectonic settings of the Dahalajunshan volcanics and granitic intrusions from the Adengtao area in the Southeast Zhaosu, western Tianshan Mountains.
西天山昭苏东南部阿登套地区大哈拉军山组火山岩及花岗岩侵入体的地球化学特征、时代和构造环境

The volcanic rocks of the Dahalajunshan Formation from the Adengtao area (Southeast Zhaosu) in the Chinese western Tianshan Mountains are dominantly composed of basaltic andesites which are characterized by enrichment of large ion lithophile elements (LILE), strong depletion of high field strength elements such as Nb, Ta and Ti and highly fractionation of rare earth elements (REEs). These basaltic andesites are intruded by some K-feldspar granite and granite porphyry dykes. The K-feldspar granite dykes are metaluminous and have high Na2O+K2O, light rare earth elements (LREEs), Zr, Nb and Y contents, high FeOT/MgO and Ga/Al ratios, and both the granitoids are depleted in Ba, Sr, P, Ti and Eu. The granitoids (K-feldspar granite and granite porphyry) give Laser-ICPMS zircon U-Pb ages of 354.2±2.3Ma and 339.5±2.3Ma respectively, indicating that the surrounding Dahalajunshan volcanics were formed no later than the earliest stage of the Early Carboniferous. It is proposed that the volcanic rocks of the Dahalajunshan Formation and the Early Carboniferous A-type granites from the Adengtao area in the Southeast Zhaosu were probably formed in a back-arc extensional environment of an active continental margin, based on a combined analysis of the field observations, regional tectonics, and the geochemistry and ages of the rocks.