Deformation Model of Contraction Structure of West Kunlun Piedmont Thrust Belt in Southwestern Depression of Tarim Basin

Through comprehensive analysis of the surface geology,seismic profile and continuous electromagnetic profile(CEMP) data in west Kunlun piedmont thrust belt in southwestern depression of Tarim basin,a non subduction-like contraction structure interpretation model with the layering contraction and vertically stacking style is proposed,which means that different styles of structural contraction and deformation occur in shallow and mid-deep layers owing to the detachments caused by the salt-gypsum rocks of Upper Cretaceous-Paleocene and competent strata's distribution in vertical direction.It seems that the detachment fault could not be stacked with another regional detachment fault whose horizontal displacement is great.The Cenozoic competent strata above the shallow salt layer are dominated by decollement fold deformation,which appears near perpendicular and symmetrical long-axis anticline,being parallel to the orogenic belt.The Mesozoic of middle subsalt layer and the deep basement rock formation in this basin are dominated by tenacious contraction deformation,and a series of basement-involved thrust faults with high-angle dipping to West Kunlun are developed.Thrust uplift may be formed in the upper wall,and a series of branch synthetic faults which constitute the imbricate wedge fan are developed in the foot wall.Finally,these thrust faults terminate in the gypsum-salt rocks below the back-thrust fault.The high-angle basement-involved thrust faults have been formed by the reverse displacement of pre-existing normal faults,which dominate the local structural deformation in the foot wall.The occurrence of high-angle thrust and the reverse of the pre-existing normal fault may be related to the vertical shearing caused by the uplift of West Kunlun.