Lhasa-Qiangtang collision: Constraints from Late Cretaceous red beds in Asa, Tibet

The continent-continent collision between Lhasa plate and Qiangtang-Baoshan plate has been a spotlight in the study of Tibetan Plateau's formation and evolution.In Asa area, Late Cretaceous Jingzhushan Formation and Mamole Formation are the most representative deposits in that time.However, the limited research on their ages and sedimentary environment has limited the understanding of the regional tectonic background.This paper reports the studies on the age and sedimentary environment of the Late Cretaceous Jingzhushan Formation in Asa of Tibet.The detrital zircon LA-ICP-MS U-Pb dating results show that the smallest single grain zircon obtained from the Jingzhushan Formation yields age of 89±5 Ma.The diorite dyke intruding into the south part of Jingzhushan Formation gives a zircon U-Pb age of 88 Ma, which further indicates that the sedimentary age of the Jingzhushan Formation in this area should be around 90 Ma.Combined with the research results of the contemporary Mamole Formation in this area, it is suggested that the Jingzhushan Formation was deposited in the alluvial fan environment, while the Mamole Formation in the braided river-delta environment.In terms of sediment sources, the source of Jingzhushan Formation tends to be an island arc provenance under converging environment, while the Mamole Formation has a more complicated source.The Jingzhushan Formation and the Mamole Formation, as the sedimentary response of the Lhasa-Qiangtang plate collision orogeny on the surface, jointly record the crustal uplift process in the Late Cretaceous.