Abstract:

Based on kinematic and geochronologic analyses of the strike slip thrust deformation system in eastern Qinghai Tibet plateau, and in combination with the study of neotectonic deformation characteristics in North China,this paper proposes a 3-stage kinematic model of east-ward squeezing-out tectonism in eastern Qinghai-Tibet Plateau during the late Cenozoic,describes the presentation of tectonic deformation and pattern of block movement occurring in each squeezing-out stage,and discusses the control of squeezing out tectonism on late hydrocarbon accumulation in rift basins in eastern China.The first squeezing-out stage that occurred during the middle and late Miocene(12～5 Ma)was remarkably characterized by tectonic deformations of strong left-lateral strike-slip movement of Xianshuihe fault zone,right lateral strike slip movement of Honghe fault,and east-ward squeezing-out of Chuan Dian(Sichuan-Yunnan)block.This tectonic squeezing-out stage resulted in counterclockwise rotation of South China Block,and led to the development of right-lateral extensional-shear stress field in the northern shelf of South China Sea and reactivation of the near E W trending extensional fault system in Pearl River basin.The second squeezing out stage that occurred during the Qinghai-Tibet movement in Pliocene and Early Pleistocene(about 4～0.8 Ma),was characterized by prominent tectonic deformations,such as strong left-lateral strike-slip movements of Kunlun-Qinling fault system and Haiyuan fault,counterclockwise rotation of the sub-blocks in North China,extensional deformation of the graben system in periphyery of Ordos block,right-lateral shear movement of the NNE faults in Bohai Bay basin, and right-lateral strike slip movement of Tanlu fault.This tectonic squeezing-out stage led to the clockwise rotation of South China block.The third squeezing-out stage that occurred since middle and late Pleistocene resulted in the clockwise and turbine like rotation of Chuan-Dian block around the late Himalayan east tectonic belt,strike-slip movement of Minshan-Longmenshan tectonic belt with weak crust shortening,and weakening of eastward squeezing-out of South China Block.These three Cenozoic tectonic squeezing out stages have heavily influenced the development of fault basins and late hydrocarbon accumulation in the offshore shelf in eastern China.

Key words: squeezing-out tectonism, Qinghai-Tibet Plateau, South China Block, North China area, Tanlu fault, Late Cenozoic, late hydrocarbon accumulation