An Analysis of Distributed Strike-Slip Shear Deformation of the Qaidam Basin, Northern Tibetan Plateau

The interior structure of the Qaidam Basin records kinematic information related to the regional deformation of the northern Tibetan Plateau. Based on balanced cross sections and depth structure maps covering two individual anticlines in the western Qaidam Basin, we calculate shortening and strike-slip amounts on the structures. Strain analyses reveal a complex deformation mechanism for them, comprising similar to 7 degrees-10 degrees clockwise rotation and oblique convergence, with block rotation having contributed more to the sinistral slip than has oblique convergence. Considering the similarities in geometry, kinematics, and onset time of the pervasive northwest trending structures within the basin, we propose that they were developed during distributed dextral shear that has affected the Qaidam Basin since the early Miocene. The bulk shear strikes at similar to N55 degrees E, which is consistent with the northeastward decrease in gravitational potential energy away from the central Tibetan Plateau, and is facilitated by the movement on the Altyn Tagh and eastern Kunlun faults. Plain Language Summary The conceptual model of distributed strike-slip shear deformation has been tested in analog experiments and is thought to be relevant to regions affected by major strike-slip faults. However, whether this phenomenon is taking place on the Tibetan Plateau during continental collision remains uncertain, due mainly to insufficient kinematic constraints on local structures. We examine faults and anticlines in the western Qaidam Basin on the northern Tibetan Plateau. We find that the pervasive northwest trending structures in the basin show similarities in structural architecture and onset time. We retrace the deformation process based on kinematic calculations for the structures using subsurface exploration data. The results reveal that both clockwise rotation and oblique convergence have contributed to deformation of the structures and that block rotation has contributed more to the sinistral slip than has oblique convergence. We infer that this scenario reflects the outward decrease in gravitational potential energy away from the central Tibetan Plateau since the early Miocene, which gives rise to the northeastward dextral distributed strike-slip shear deformation of the Qaidam Basin. The Altyn Tagh fault acts as a relatively free boundary to the Qaidam Basin, while the eastern Kunlun fault transfers continuous, but laterally changing strain to the Qaidam Basin.