DEM MODELING OF KUQA SALT-RELATED FOLD-AND-THRUST BELT, CHINA

Shortening in the southern foreland of the Central Tienshan resulted in a representative thin-skinned compressive structure: Kuqa Cenozoic fold-and-thrust belt (FTB), which comprises northern monocline, Kelasu anticline, Baicheng syncline, and Qiulitake anticline. Field and seismic investigations show that widely distributed Paleogene rock salt has a significant impact on the deformation in this area. Structural styles are quite different in the strata beneath and above salt. Strata above salt are mainly deformed by broad folding, while strata beneath salt are mostly deformed by closely-spaced thrusts. However, our understanding of the structural evolution and deformation mechanism of Kuqa FTB is very limited, but is of great interest due to the hydrocarbon exploration. In this research, we ran a series of discrete element method (DEM) simulations to explore the geometric patterns, structural evolution, and deformation mechanisms of Kuqa FTB. Numerical models are initially 80 km long and 5 km high, comprising sub-salt Jurassic to Cretaceous strata, Paleogene salt layer, and Paleogene to Neocene strata. The numerical strata were deformed by displacement of one wall, simulating horizontal compression and total shortening of 30 km. After 8 km of shortening, growth sediments were added. The DEM models reproduced major structural features observed in the Kuqa FTB. The sub-salt Mesozoic strata were mainly deformed by closely spaced imbricate thrusts. The Cenozoic strata above the salt layer were deformed by broad folding and low-angle thrusts. The modeling results indicate that salt structures near the back end, i.e. Kelasu anticline, were the result of regional compression, whereas salt structures near the front end, Qiulitake anticline, were controlled by growth sedimentation in the nearby Baicheng syncline. With insights from DEM results, we suggest that Kuqa FTB is mostly thin-skinned with Paleogene salt as decollement, except near the backstop, where Mesozoic strata below salt are faulted and folded, and hence form structural traps for oil and gas. The prospects for finding Kelasu-type structural traps in Qiulitake are limited.