From Left Slip to Transpression: Cenozoic Tectonic Evolution of the North Altyn Fault, NW Margin of the Tibetan Plateau

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.

Lower Crustal Rheology Controls Strain Partitioning and Mode of Intracontinental Deformation

“…Conversely, the eastern Tarim Basin does not display thick Cenozoic sediments, which is more consistent with strike‐slip deformation without significant thrust‐induced loading. Just north of the Altyn Tagh Range is minor subsidence and related sedimentation observed in the gravity and sediment maps (∼3 km) that reflects loading of the Tarim Basin caused by the transpressional deformation observed within this bend in the ATF (e.g., Cowgill et al., 2004; Gao et al., 2022). These observations suggest that the ranges around the western Tarim Basin have experienced more shortening and foreland‐loading throughout the Cenozoic, and thus the present‐day strain patterns have persisted throughout the Cenozoic.…”

Limited Northward Expansion of the Tibetan Plateau in the Late Cenozoic: Insights From the Cherchen Fault in the Southeastern Tarim Basin

“…The kinematic model of the North Altyn fault suggests it is a lift‐slip transpressional fault since ca. 17–15 Ma (Cowgill et al., 2000; Gao et al., 2022). Thus, the post‐Miocene vertical and strike‐slip rates of the North Altyn fault are ∼0.13 mm/a and ∼1.67 mm/a, respectively.…”

“…Based on field observations and seismic data, Gao et al. (2022) determined that ∼2 km vertical uplift and ∼25 km strike‐slip displacement have been absorbed by the North Altyn fault. The kinematic model of the North Altyn fault suggests it is a lift‐slip transpressional fault since ca.…”

“…The Altyn Tagh fault system may initiate in the Eocene (ca. 49 Ma) (Cheng et al., 2015; Yin et al., 2002), with a possible tectonic reorganization in the middle Miocene (Darby et al., 2005; Gao et al., 2022; Wu et al., 2019; Yue & Liou, 1999). The total displacement along the Altyn Tagh fault may be over 450 km (Cowgill et al., 2003; Yue et al., 2005).…”

Jurassic sedimentary migration characteristics and their geodynamic implications in the Dunhuang Basin and adjacent regions, Northwestern China

“…Wang et al, 2005;Yin et al, 2002;Yue & Liou, 1999;Yue et al, 2010;Zhou & Graham, 1996). Based on the apatite fission track data obtained from the Altyn Tagh Range and its neighbouring basins, recent studies suggested the primary strike-slip motion occurred along the North Altyn Fault instead of the ATF during the Paleogene (Gao et al, 2022;Wu et al, 2019). However, there is little research on the Mesozoic, espe-…”