Geological and tectonic evolution of the basement in the Qiangtang basin of northern Tibet: Evidence from detrital zircon U-Pb isotope chronology of sandstone in the Jurassic Yanshipin Group

As the largest Mesozoic-Cenozoic basin in the Tibetan Plateau, the Qiangtang Basin is the key area to reveal the evolution of Tethys, and hence its structure and evolution have aroused much interest. However, for a long time the problems concerning the existence or nonexistence of the pre-Cambrian basement in the Qiangtang Basin and its tectonic evolution have been topics of much controversy. Yanshiping Group is the most widely distributed strata which have the most complete set of Jurassic in the Qiangtang Basin, and its detrital sediments contain a lot of important information concerning the tectonic evolution of the Qiangtang Basin. The authors hence selected the sandstone from Yanshiping Group in the east of the Qiangtang Basin, the northern foot of the Tanggula Range in the Wenquan region to perform LA-ICP-MS U-Pb dating so as to provide an important basis for solving tectonic evolution about the basement in the Qiangtang basin. The ages of 429 valid test points from 8 sandstone samples show that the formation of detrital zircons from Yanshiping Group spanned a long period, and the ages of zircons range from New Archean to Late Middle Jurassic (2668-166 Ma), which have evident stage characteristics and can be divided into ten age groups. In combination with regional geology, the authors discussed and analyzed detrital zircon whose ages are greater than 486 Ma. It is held that the Qiangtang Basin has Pre-Cambrian basement, the main period of its formation is approximately 1974-1666 Ma, and the Pre-Cambrian basement also suffered from the post-tectonic reformation, and experienced the tectonic thermal events of the Columbia and Rodinia supercontinent, Greenville-Jinning tectonic movement of magma, Pan-African movement and a series of tectonic evolution. The results obtained by the authors support the opinion that the Qiangtang terrane belongs to the Gondwana.