Development and growth of basement-involved structural wedges in the northwestern Qaidam Basin, China

Abstract

Structural wedges contain two connected fault segments, a fore thrust and back thrust, that bound a triangular- or wedge-shaped fault block. Coeval displacements on both faults drive the wedge into surrounding rock, causing distinctive patterns of uplift and folding. We identified a series of thick-skinned structural wedges in northwestern Qaidam Basin, China, where syntectonic strata record deformation timing and kinematics. The Qaidam Basin is located at the northern margin of the Tibetan Plateau and contains more than 100 large anticlinal structures, many of which exhibit characteristics of structural wedges. We interpreted and modeled these structures using seismic reflection data, well logs, surface geological exposures, remote sensing images, and digital elevation data. These wedge structures are distinguished by having elevated and deformed strata in the footwalls of the back thrusts and synclinal folds that extend upward from the wedge tips. With the constraints of fold shape, growth strata, structural relief, and shallow fault geometry, we developed a series of forward models that describe the geometry and kinematic evolution of these wedge structures. The analysis suggests that some of the wedge structures reactivate preexisting normal faults. Our results provide a better understanding of how to identify thick-skinned wedge systems and model their geometry and kinematic evolution, which has implications for studying the tectonic history of the basin. Understanding the geometry and kinematics of the wedge structures is also crucial for petroleum exploration because both hanging-wall and footwall traps constitute an important component of current exploration targets.