An Evolving Lithospheric-Scale Wrench Fault System Along the Eastern End of the Altyn Tagh Fault: Kinematics and Quaternary Activity of the Heishan Fault System, Western China

The Altyn Tagh fault (ATF) is a major intracontinental strike-slip fault system that defines the northern margin of the Tibetan Plateau. The fault system loses its obvious surface expression north of the Qilian Shan fold-and-thrust belt, but may link eastward with multiple faults in the northern Hexi Corridor and southern Alxa block. To better understand the potential connectivity and displacement transfer between the ATF and the northern Hexi Corridor fault array, we carried out a multidisciplinary field and remote sensing-based investigation of the actively deforming Heishan and Jinta'Nanshan region north of Jiayuguan City. We document Quaternary sinistral strike-slip motion on the Heishan fault (HF) system and active sinistral transpression within a 70-km-long, E-W deforming belt east of the Heishan, which is characterized by multiple left-stepping, en-echelon Quaternary folds and linking faults. Cosmogenic Be-10 dating of displaced terrace surfaces yields a vertical slip rate of similar to 0.2 mm/a for the northern Heishan thrust and a sinistral strike-slip rate of 0.6 +/- 0.2 mm/a for the HF. Within the uplifted core of the Heishan massif, the HF contains ductilely deformed Paleozoic basement lithologies with dextral-sense shear fabrics that indicate that the modern HF has reactivated and inverted an older shear zone. A previously published magnetotelluric profile across the HF system suggests that it roots into a steep, deeply penetrating fault that is unlinked to the Qilian Shan thrust wedge. Instead, we suggest that the active sinistral deformation belt of the Heishan-Jinta'Nanshan represents the eastward-evolving, upper crustal expression of the modern ATF system.