Interactions between thin- and thick-skinned tectonics at the western Sichuan Basin, China

This study investigates the geometry, kinematics, and interaction of thin- and thick-skinned tectonics at the western Sichuan Basin adjacent to the eastern margin of the Tibetan Plateau. A two-level detachment system, comprising a shallow Triassic and basal Precambrian detachment, was identified. Three-dimensional (3-D) structural modeling was applied to demonstrate the geometry of the shallow detachment that developed in the Sichuan foreland basin. The shallow detachment forming material is an evaporite sequence deposited in the Middle Triassic, which was subsequently buried beneath the foreland basin and later subsided rapidly during the flexural loading process during the Late Triassic. In the Cenozoic, this set of evaporite rocks developed into an effective shallow detachment, transferring geologic slip from the Longmen Shan range front to the Sichuan Basin. The structure of this shallow detachment exhibits an asymmetrical characteristic, with its deepest location consistent with the Mesozoic foreland depression. This relationship indicates that foreland subsidence in the Late Mesozoic is the main factor controlling the geometry of the detachment. In the southern Cenozoic foreland basin, the development of thrust faults above the Precambrian basal detachment resulted in a local deformation and uplift of the shallow detachment, resulting in a lower basal slope (0.5 degrees-1 degrees) of the sedimentary basin taper and a high internal distribution. In contrast, the sedimentary basin taper in the north has a high basal slope that mainly translates along the shallow detachment, lacking thrusting-related structures. This study reveals that the preexisting stratigraphic architecture of the sedimentary basin can influence the subsequent structural deformation of the foreland basin. This has important implications for other foreland basins with multistage crustal shortening processes.