Continent-continent collision at the southwestern margin of the Cretaceous Qiangtang terrane: Constraints from granite in the western Bangong-Nujiang Suture Zone

A large number of moderately felsic to basic intrusive rocks in the forms of rock strains or rock branches are distributed in the southwestern margin of the Qiangtang terrane. These intrusive rocks are characterized by petrographic analysis as peraluminous granite with low SiO2 (67.99%-73.32%) and high Al2O3 (12.82%-15.02%) contents, and defined as calc alkaline based on the Ritmann serial indices of 2.09-2.63 (σ<3.3). They show strong enrichment of light rare earth elements (REE) and strong depletion of heavy REE, with a high degree of magma crystallographic differentiation. The geochemical characteristics of the rocks and REE in granite indicate its tectonic environment is mainly type I, with some variability, and its formation and intrusion should be related to the closure of the ancient Tethys Ocean and the expansion of the new Tethys Ocean, which suggests an intracontinental collisional orogenic granite origin. The zircon laser ablation inductively coupled plasma-mass spectrometry (LA-ICPMS) dating of several granite masses in this area yielded a formation age of 107-116 Ma, which is consistent with the time of continent-continent collision at the southern margin of the Qiangtang terrane in the late Early Cretaceous. © 2022, Editorial Office of Earth Science Frontiers. All right reserved.