Late Cenozoic tectonic events in east Tibetan Plateau and extrusion-related orogenic system

This paper revised the chronology of major late Cenozoic tectonic events in east Tibetan Plateau, mostly based on records of stratigraphy in the basins and magmatism and deformation along active fault zones, with the purpose of establishing an evolution history of extrusion-related orogenic system. It is shown that the most important event, as previously named the Qingzang movement, was initiated at 12-8 Ma and lasted to early Pliocene, with a duration of 6-8 Ma. The crustal fragments in east Tibet, such as the Chuan-Dian, Chuan-Qing, Longzhong blocks, were orderly extruded eastward accommodated by large-scale sinistral strike-slip faults like the Xianshuihe, East Kunlun and Haiyuan faults. This eastward extrusion was concomitant with thrusting, which resulted in fast uplift of the ranges along its eastern edges, and went beyond this margin through decollement, generating folds of the cover rocks like the Longquanshan, Daliangshan in the Yangze craton. The deposition of late Pliocene conglomeratic layer, namely the Dayi conglomerates along the eastern foreland zone, the Jishi conglomerates and the Wuquan conglomerates at the northeast corner of Tibet, marked the emergence of contrast geomorphology in this region. Late Pliocene to early Pleistocene (3.6-1Ma) corresponds to a period of tectonically quiescence or relaxation, during which a set of N-S trending rift basins, such as Yuanmu, Yanyuan, and Anninghe, were developed along the eastern margin, and accumulated a series of fluviao-lacustrine facies deposits in these basins. This relaxation stage was followed in Early-Middle Pleistocene (1.0-0.6 Ma) by an important compressional event named the Kun-Huang or Yuanmu event, which caused further uplift of east Tibet. Active faulting pattern in east Tibet has been changed greatly since the late Pleistocene (about 120 Ka), featured along its southwest part by clockwise rotation around the east Himalaya syntax of two sinistral strike-slip fault zones, and along its central north part by a counter clockwise rotation accommodated by dextral strike-slip motion in the Longmenshan fault zone and eastward push of the Qinling range. The lower crustal flow could be a major driven mechanism for the deformation of this most recent stage.