Zircon U-Pb dating for the Quxu granitic complex in the Gangdise belt, Tibet, and its geological significance

The Quxu granitic complex is located at the southern margin of the eastern Gangdise tectonic-magmatic belt. Magmatic activities of the Quxu granitic complex were closely related to the northward subduction of the Neotethys and the Indo-Asian collision. In this paper, a systematic study of LA-ICP-MS zircon U-Pb geochronology and petrochemistry have been carried out on the intermediate-acidic granites widely distributed in the Changguo village, east of Quxu county. The results show that the Quxu complex is characterized by three stages of granitoids with different ages and scales. The zircon U-Pb ages of LA-ICP-MS are 95.2 ±1.0 ~ 88.5 ±1.0Ma, 65.2 ±0.6Ma and 48.5 ±0.5 ~ 43.3 ±0.7Ma, respectively. The results of petrochemistry show that the late Cretaceous and Paleocene granites are mainly neutral to intermediate-acidic, calc-alkaline series, with the characteristics of medium aluminum, A/CNK less than 1.1, belonging to I-type granites, which are the products of partial melting of basaltic lower crust formed in the arc tectonic setting during the subduction of the Tethyan oceanic crust. The Eocene granites are mainly high-Kcalc-alkaline series as well as shoshonitic series and are metaluminous to peraluminous, which indicate that the magma was formed in the collisional setting of India-Eurasia plates and mixed with crustal materials at different degrees during the magma underplating processes.