Zircon U-Pb Age, Geochemistry and Geological Implications of Granitoids in Tuerkubantao, Xinjiang

Three types of granitoids were recognized in Tuerkubantao(土尔库班套) district, located on the northwestern margin of the Junggar Block. The zircon U-Pb age of the three types of granitoids suggests that they formed in different orogenic stage in response to the convergence and collision between Siberian and Kazakhstan plates. Biotite granite is similar to the volcanic arc granites in composition, with zircon U-Pb age of 382.8±2.5 and 355.6±2.4 Ma. The former is crystallizing age of the volcanic arc granite, while the later record the time of hydrothermal alteration induced by a later magmatism. The granite is severe altered and its zircon grain get a lower intercept age of 324.4±7.3 Ma, which is possibly coursed by magmatism in syn-collision. The rhyolite with composition similar to A-type granites in adjacent area, crystallized at 295.9±1.4 Ma, is possibly the extrusive phase of A-type granite formed in the post-orogenic tectonic setting. The granitoids in Tuerkubantao area record the evolution of the northwestern Junggar orogen. The area has been in convergence setting from Middle to Late Devonian, and stepped into syn-collisional tectonic setting in Early Carboniferous, finally evolved into the post-orogenic tectonic stage since Early Permian.