The JinheaQinghe faultaAn inactive branch of the XianshuiheaXiaojiang fault zone, Eastern Tibet

The XianshuiheaXiaojiang fault zone (XFZ) forms a prominent linear NWaSE trending tectonic feature along the southeastern margin of the Tibetan Plateau. The spatial and temporal evolution of the predominantly strikeaslip movement along the fault remains unclear, as estimates for the initiation age of its different segments range from 5 to 13 Ma. The JinheaQinghe fault (JqF; the south part of the Longmen Shan thrust belt) provides a key for understanding the tectonic role and deformation history of the XianshuiheaXiaojiang fault zone in terms of timing, magnitude of displacement, and spatialatemporal evolution. This paper presents research on the structure and chronology of the JqF. The results of a geometric and kinematic study of the JinheaQinghe fault show it to be a thrust fault with a left-lateral strike slip component; The strike slip offset extends at least 13a18 km to southwest, based on the shortening of its folds and faulting, and based on stream deflection. Ten apatite fission track apparent ages show a pronounced change in age/elevation gradient at ~ 17-2 Ma, consistent with an abrupt increase of exhumation due to uplift of the hanging wall of the JqF at that time. Combined with the age of deformed Tertiary strata in the footwall of the JqF and the geometric relationships of the JqF with the Chenghai fault and the XFZ, this indicates that the JqF was active between 17 and 5 Ma. Based on the fault chronology, geometry, and movement, we suggest that the fault was a transpressional structure at the south end of the XFZ during the period from 17 to 5 Ma.