Differences in east-west thermo-rheological structure and lithospheric deformation in the Qaidam Basin, Northern Tibetan Plateau, China

Abstract

To investigate the differences in east-west lithospheric deformation in the Qaidam Basin, we present thermo-rheological models of two profiles across the western Qaidam Basin (WQB) and eastern Qaidam Basin (EQB). The differences in east-west geodynamic deformation styles are also described, involving GPS motions, focal mechanisms (P axes), seismic anisotropy (SKS-wave splitting), and low-velocity zones (LVZs). The WQB is characterized by a warm destabilized cratonic basin with a weak lower crust, and the rheological structure changes from a rather weak crème brûlée-1 regime into a strong jelly sandwich-1 regime, from the Altyn-Qaidam boundary to the northeastern corner of the WQB. Combined with the limited distribution of the LVZs and the strong crust-mantle decoupling revealed by the unmatched pattern between P axes (N20ºE) and SKS-wave splitting (N110°E), the crust-mantle mixing related to the under-thrusting of the Tarim Basin along the Altyn Tagh Fault is suggested as the primary tectonic dynamic inducement of the destabilized WQB craton, which weakens the lithospheric strength greatly and contributes to the shallow brittle deformation. However, the EQB performs as a typical cold and rigid cratonic basin characterized by a jelly sandwich-2 rheological regime, which is sufficiently strong to maintain crust-mantle coupling. The LVZs beneath the EQB revealed by recent wide-angle seismic profiles have only a small effect on the lithospheric strength drop. The EQB could be regarded as a solid basin, anchored in the NE Tibetan Plateau, which shows a strong resistance to NE extrusion of the weak plateau material, leading to clockwise rotation.