摘要
West Qinling is located at the tectonic transition from transpression to transtension in NE Tibet,and thus it is a key locality for understanding the outgrowth of the Tibetan Plateau in the late Cenozoic.As a consequence of the northeastward expansion of NE Tibet,the Neogene basins developed along West Qinling recorded the information of this tectonic outgrowth.In this paper,we chose the Anhua-Chengxian Basin as an example for detailed analysis of the sedimentation and tectonic deformation.A two-stage tectonic evolution history was distinguished for this Neogene basin.During the early stage at 10-4 Ma,transtensional sinistral strike-slip occurred along the Diebu-Bailongjiang-Chengxian-Taibaishan fault resulting in the formation of the Anhua-Chengxian Basin.At the same time other basins such as the Hanzhong,Wushan,Tianshui and Xihe basins were initiated respectively along the Qingchuan fault,the northern Qinling fault,the Lixian-Luojiabao fault and the Xihe fault.These strike-slip faults might have propagated eastward and controlled the NW-SE extension in the Weihe graben at 10-4 Ma and fast uplift of the Mts.Huashan and Taibaishan along the southern margin of the Weihe graben.During the time span of 4.2-2.5 Ma,due to the kinematic adjustment of the regional tectonics stress field,the Neogene basins in West Qinling were tectonically inverted by NE-SW compression.Thus,the formation and deformation of Neogene basins in West Qinling obviously recorded the process of tectonic extrusion of NE Tibet in the late Neogene.
