Abstract: The Qiangtang Block has become a geological research hotspot in recent years, however, its tectonic attributes, as well as the existence of ArcheanProterozoic basement in the block, have been controversial. In this work, using LAICPMS zircon UPb technique, we performed detrital zircon dating for the sedimentary samples from the Rigain Pünco Formation in the Niu Mountain in Rongma, Tibet. The results show: (1) The youngest age of detrital zircon is 215±2 Ma, equalling the maximum deposition age for the Rigain Pünco Formation. Combined with regional geological data, the deposition period was determined to be coincide with the Late Triassic NorianRhaetian stage. (2) The zircon grain age ranges between 580±6 and 212±2 Ma. The age peak at 298±2 Ma indicates the area was affected by the crustal thinning extensional stage magma activities during the PaleoTethys evolution in the Early Paleozoic. The age peak at 442±3 Ma shows that the area was affected by the magmatic activity due to the collision and accretion of the Caledonian Yangtze and Cathaysian plates in the Middle Paleozoic, and the provenance of the clastic rocks was the Yangtze continental margin. There is only one age occurrence at 650500 Ma, suggesting the provenance region was almost unaffected by the panafrican magmatism. (3) Clastic zircon appears in relatively small amount and ages from 1091±6 to 757±6 Ma, showing that the area was affected by the tectonic magmatic thermal events of the GrenvilleJinningian in the southern Qiangtang Block. (4) A large number of detrital zircons are dated between 3214±7 and 1380±15 Ma, they account for 60% of total zircon samples from the Rigain Pünco Formation. The age peaks at 1875±5 and 2531±6 Ma show that, the Qiangtang block was affected by the Proterozoic crystalline basement main stage tectonicthermal events, and the late Archean supercontinent split global events, hence providing a strong evidence for the existence of ArcheanProterozoic basement rocks in the Qiangtang Block.

Key words:  Niu Mountain of Rongma Area, Tibet, Rigain Pünco Formation, clastic zircon dating, sedimentary age, provenance, Archean-Proterozoic basement