Tectonic Evolution of the Thrust-Nappe Belt in the Southwestern Ordos Basin (China): New Constraints from Exploration Seismic Data

The thrust-nappe belt in the Western Ordos Basin is located in the northern segment of the North‒South structural belt in the mainland China. It is the junction of different tectonic units. The structural evolution of the region is significant to the knowledge of regional geology as well as to oil and gas exploration initiatives. However, due to insubstantial data, the structural evolution of the region is still controversial. In our study, the stratigraphic age was constrained via new drilling data, which allowed newly acquired 2D high-precision seismic data to be interpreted, revealing the tectonic evolution history of the thrust-nappe belt on the Southwestern Ordos Basin. Our results show that the thrust-nappe belt originated from the south‒north trending aulacogen developed during the Meso-Neoproterozoic age. The main fault in the aulacogen experienced two stages of compressional inversion deformation at the end of Triassic and in the Late Jurassic. At the Late Triassic, pre-existing extensional faults experienced the low intensity compressional inversion, and the low-amplitude fold deformation occurred on the western margin of the basin, which was strong in the south and it was weak in the north. The Late Jurassic compression deformation resulted in the large-scale inversion and thrust-decollement of preexisting main faults, and produced a large number of new thrust faults and several thrust nappes, resulting in the strong uplift and denudation on the front of the nappes. Comparing the two stages of compression, we reveal that the Late Jurassic compression was the main tectonic event that created the thrust-nappe system and the present basin-mountain system in the southwestern Ordos Basin.