New Geochronologic and Paleomagnetic Results From Mesozoic Rocks of the Qiangtang Terrane: Implications for the Pre-collisional History of the Central Northern Tibet

The Qiangtang terrane of Tibet is a critical region for tectonic reconstruction of Asia. Our knowledge about tectonic history prior to India-Asia collision is limited as most studies focused on post-collisional history of the region. Here, we report our new geochronologic data from 3 localities of volcanic rocks in northern Qiangtang and summarize paleomagnetic results from these volcanics and relevant sedimentary rocks. 40Ar/39Ar dating by step-heating shows that the volcanic rocks and a subvolcanic granite in Wudaoliang area are coeval with the basaltic rocks in Kaixingling region to the south, revealing that volcanism in this province of Qiangtang began at least 210 Ma ago. Whether these melts are the product of collision between the Qiangtang and Kunlun blocks or intracontinental rifting remains a topic of active research. Our new 40Ar/39Ar age for a basalt flow at Tuotuo He region indicate the lava flow erupted around ca. 135 Ma, signifying they may relate to Lhasa-Qiangtang convergence in Late Jurassic/earliest Cretaceous time. Our paleomagnetic data from these dated rocks suggest that the Qiangtang terrane did not occupy its current position in terms of paleolatitude in both Triassic and Jurassic times, and suggest significant separation between Qiangtang and surrounding Asian blocks during Triassic through Late Jurassic.