Indosinian granitoids in the Zhidoi area in the northern segment of the Sanjiang belt, Qinghai: Their petrogenesis and zircon U-Pb dating

Abstract：The regional geological survey at a scale of 1∶250000 in the Zhidoi area in the northern segment of the Sanjiang belt, Qinghai Province, suggests that the extensively exposed intrusive rocks in the area mainly formed in the Late Triassic. According to the single-zircon U-Pb dating, granodiorite and porphyritic monzogranite in the Bayan Har terrane in the northeast of the Zhidoi area have ages of 212.38±7.1 Ma and 196.8±0.3 Ma respectively, and quartz diorite in the Jinshajiang ophiolitic mélange zone in the southwest of the Zhidoi area has an age of 215.4±0.8 Ma. Based on the geology, petrology and geochemistry of the protons, combined with the characteristics of regional tectonic evolution, it may be preliminarily determined that: these late Indosinian-early Yanshanian granitoids formed in a post-collisional stage; the magma has the feature of multiple sources and its formation may be related to lithospheric delamination.