No abstract

No abstract

The Cenozoic North Altyn Fault (NAF) is a major splay of the Altyn Tagh Fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India‐Eurasia collision is highly debated. Here, we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km of the NAF. Seismic surveys reveal minimal Cenozoic shortening in the subsurface of the Southeast Tarim Basin and support for large‐scale (>120 km) left slip on the NAF. Based on the satellite imagery, two new faults are identified to define the northern boundary of the NAF system, which together with the NAF to the south constitute a narrow transpressional shear zone comprised of three basement‐cored, fault‐bound slivers. Fission track data and thermal modeling indicate that the NAF zone experienced broad reburial during early Cenozoic that was locally interrupted by ∼40 to 35 Ma exhumation proximal to the NAF, followed by widespread but heterogeneous exhumation since ∼17 to 15 Ma associated with ∼9 to 11 km of total shortening across the NAF system via thick‐skinned faulting. We conclude that the NAF initiated as a left‐slip fault at ∼40 to 35 Ma and then became transpressional at ∼17 to 15 Ma during the middle‐Miocene reorganization of the Altyn Tagh Fault system. We find no evidence to support prior inferences of large‐scale (∼100 km) underthrusting of the Tarim Basin beneath the Tibetan Plateau along the NAF.

The northern margin of the Tibetan Plateau is defined by the left‐lateral Altyn Tagh fault. It remains unclear whether the Cenozoic deformation related to the India‐Asia collision has remained stationary along the Altyn Tagh fault or propagated northward into the southeastern Tarim Basin. The Cenozoic Cherchen fault is located in the southeastern Tarim Basin, ∼90–120 km north of the Altyn Tagh fault, and thus, may play a critical role in addressing this issue. Here, we used a densely‐spaced two‐dimensional seismic reflection survey to investigate the geometry and kinematics of the Cherchen fault and understand its role in the expansion of the northern margin of the Tibetan Plateau. Our seismic study shows that the Cenozoic Cherchen fault is a high‐angle left‐lateral transpressional fault. Kinematic analysis of the Cherchen fault suggests that a restraining bend structure has formed along its central segment. Stratigraphic records suggest that the Cherchen fault initiated in the Paleozoic and reactivated during the middle Miocene (ca. 17–15.7 Ma). We infer that the dip‐slip and strike‐slip rates of the Cherchen fault are ∼0.09 mm/a and ∼1.66 mm/a, respectively. A regional cross section reveals that the northward expansion of the plateau is ongoing, but the range is limited to ∼90–120 km. We interpret that middle Miocene tectonic activity throughout the region was also concentrated along the northern plateau margin, defined by both northeast‐directed crustal shortening and northward expansion of the plateau.