关键词: 库车坳陷, 先存被动盐底辟, 离散元, 应力应变, 构造变形

Abstract:

Kuqa fold-thrust belt is a typical complex salt-bearing fold-thrust system. In this paper, based on seismic interpretation, two discrete element models are designed to explore the influence of pre-existing passive salt diapir on the structural geometry and evolution of double-detachment fold-and-thrust belts, as well as the causes behind the different salt structural deformation characteristics and mechanism of the strike segment in Keshen 5 structural area, and the slip displacement of subsalt faults are analyzed finely. The simulation results show that the pre-existing salt diaper, as the priority location of compressional structural deformation and the priority area of stress release, affects the sequence of faults in subsalt layer and the slip displacement of subsalt faults, proceeding to control the differential evolution of structures along the strike. Comparing the simulation results and structural features of Keshen 5 structural area in Kuqa depression, we suggest that the Tuzimazha anticline is the result of the subsequent compressional deformation of the pre-existing passive diapir in the salt basin. The Tuzimazha anticline absorbs most of the shortening, resulting in a significant uplift of the adjacent subsalt fragments, and a wide and gentle syncline is formed on the north side of the anticline under the influence of syntectonic deposits, which suppresses the formation of disordered faults in the syncline. The pre-existing salt diapir structure is the main controlling factor controlling the tectonic deformation in Keshen 5 area. There is no pre-existing salt diapir in the eastern part of the study area, Kumugelemu anticline and Kasangtuokai anticline are developed in turn, the amplitude of which decreases towards the basin, and the slip intensity of subsalt faults weakens towards the basin. The western part of the study area contains pre-existing passive salt diapir. Tuzimaza anticline is developed, and the activity intensity of subsalt faults under pre-existing passive salt diapir is stronger than that of adjacent faults.

Key words: Kuqa depression, pre-existing passive salt diaper, discrete element method, stress and strain, structural deformation