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

Abstract

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‐échelon Quaternary folds and linking faults. Cosmogenic 10Be dating of displaced terrace surfaces yields a vertical slip rate of ∼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.

Diachronous Quaternary Development of the Jiayuguan Fault and Implications for Strain Compartmentalization and Modern Earthquake Hazards in the NW Hexi Corridor, China

“…Another interesting point is that the youngest onset age for the JYGF is ∼0.4 Ma as suggested by the age of the deformed Qf1 fan. This is compatible with the reported 0.6∼2 Ma initiation of deformation along the Jinta'Nanshan and Heishan faults to the N and NE (Hetzel, Tao, Niedermann et al., 2004; Pan et al., 2021; H. Yang et al., 2023; W. J. Zheng, Zhang, Ge et al., 2013).…”

“…To characterize the apparent structural relief along the length of the JYGF, we subtracted the elevation on the footwall profile QQ′ from the hanging wall profile PP′ at corresponding positions (cf., Ellis & Barnes, 2015; H. Yang, Yang, Huang et al., 2018). We note that these displacement values represent a minimum vertical separation due to significant sediment accumulation on the footwall of the fault as revealed by footwall topography and visible on satellite imagery (Figure 3b, cf., H. Yang et al., 2023; H. Yang, Yang, Huang et al., 2018). The along‐strike variations in cross‐fault relief reveal that the bedrock and alluvial sections both show a linear SE‐ward decrease in fault‐related uplift, but with different slopes (Figure 6b).…”

“…The profiles show that vertical separation ranges from ∼38.6 m in the northwest to ∼12.5 m in the southeast (Figure 3b). We note that these displacement values represent minimum tectonic vertical offsets because of sediment accumulations on the JYGF footwall, as shown by the footwall topography and visible on airborne imagery (Figure 3b, cf., H. Yang et al., 2023; H. Yang, Yang, Huang et al., 2018). This southeastward decrease in relief across the JYGF is consistent with the SE‐directed decrease of structural relief in Figure 6b.…”

“…The low strike‐slip rate at the east end of the ATF contrasts with the higher contractional strain rate along the Northern Qilian Shan Thrust. This suggests a first‐order partitioning of regional strain between sinistral transpression along the ATF‐Heishan‐Jinta'Nanshan system and dominantly contractional strain at the Northern Qilian Shan thrust front and in the immediate Qilian Shan foreland (Hetzel et al., 2019; Tapponnier et al., 1990; Y. Wang et al., 2020; H. Yang et al., 2023). At a more regional scale, compartmentalized faulting in the northwestern‐most Hexi Corridor defines a triangular block of active deformation where NE‐directed contractional deformation of the Qilian Shan foreland interacts with E‐W left‐lateral displacement along the Altyn‐Tagh‐Heishan‐Jinta'Nanshan sinistral strike‐slip system (H. Yang et al., 2023; W. J. Zheng, Zhang, Zhang et al., 2013).…”

“…In addition, left‐lateral displacement along the ATF is also transferred into crustal shortening in the Qilian Shan and eastward block extrusion along the Changma and Haiyuan strike‐slip faults (Hetzel et al., 2019; Hetzel, Tao, Stokes et al., 2004; Hu et al., 2015; Meyer et al., 1998; Shao et al., 2022; Q. Xu et al., 2021; X. Xu et al., 2005, H. Yang, Yang, Huang et al., 2018; H. Yang, Yang, Zhang et al., 2018; P. Z. Zhang et al., 2007; W. J. Zheng, Zhang, He et al., 2013). Although the surface trace of the ATF ends west of the Kuantanshan (Figures 1a and 1b, W. J. Zheng, Zhang, Zhang et al., 2013), Quaternary sinistral strike‐slip displacements have been accommodated further east and along‐strike in the Heishan‐Jinta'Nanshan fault array (Figure 1b; B. Zhang et al., 2016; H. Yang et al., 2023).…”