Structural coupling between the Qiman Tagh and the Qaidam Basin, northern Tibetan Plateau: a perspective from the Yingxiong Range by field mapping, seismic imaging and physical analogue

Abstract:

The Qiman Tagh and the Qaidam Basin within the Tibetan Plateau are contrasting in geomorphological, geological and geophysical features. The Yingxiong Range is the largest anticlinal belt in the SW Qaidam Basin and hold a key in understanding the relationship between these two tectonic units. Herein, we investigated the geometries, shortening, timing and mechanism of the structural deformation across the entire Yingxiong Range by integrated field mapping, interpretation of 3D/2D seismic reflection data and physical analogue modeling. The structural interpretation demonstrate that the Yingxiong Range was overall controlled by SW-dipping basement-involved reverse faults. These faults likely soled into a decollement layer at ~15-16 km depth through excess area – depth analysis. This pattern was complicated by the development of local salt layers that resulted in intense strain localization and deformation decoupling, as indicated by physical analogue modeling. Deformation initially occurred at ~8.1 Ma but strengthened at ~2.5 Ma, with a total shortening of ~5 km in the northwestern part. Together with published results, our findings revealed a NE-directed thrust system involving the Qiman Tagh and the SW Qaidam Basin, and that the Yingxiong Range likely constituted the front of this system. We further inferred that this NE-directed thrust system in the upper crust, together with a SW-directed deep reverse fault offsetting the Moho in the lower crust and upper mantle, may form southwestward-tapering wedge tectonics between the Qaidam Basin and the Qiman Tagh – East Kunlun Shan, which likely resulted from the lithospheric heterogeneities between these two units.