Oblique convergence drives left-lateral slip on the Altyn Tagh Fault: Evidence from crustal anisotropy

The Altyn Tagh Fault (ATF) system separates the Tibetan Plateau from the Tarim Basin and accommodates the northeastward expansion of the plateau. However, crustal deformation across the ATF remains poorly studied, limiting our understanding of the mechanisms driving plateau uplift and expansion. Using data from a short-period dense array across the ATF system and nearby permanent stations, we determined the crustal anisotropy by fitting the sinusoidal moveout of Pms phases in receiver functions. This approach provides key constraints on intracontinental deformation features. The average fast directions of crustal anisotropy are ENE-WNW in the eastern Tarim Block, nearly E-W in the Altyn Tagh Range (ATR), and NW-SE in the Qaidam Block, corresponding to average splitting times of 0.42, 0.61, and 0.68 s, respectively. In the eastern Tarim Block, the crustal anisotropy aligns with paleotectonic structures, reflecting fossil anisotropy preserved within the craton. The southward underthrusting of the Tarim Block and the NNE-NE extrusion of the northern Tibetan Plateau have generated pure-shear deformation within the crust beneath the northern ATR and the western Qaidam Basin, respectively, producing corresponding E-W and NW-SE crustal anisotropy. The oblique convergence between the Tarim Block and the Tibetan Plateau facilitates left‑lateral strike‑slip shearing along the central segment of the ATF as well as transpressional deformation within the ATR. This process has driven the uplift of the ATR and accommodated the outward extrusion of plateau material, thereby dominating the intracontinental deformation pattern across the northern margin of the Tibetan Plateau.