Abstract: Positive inversion structures are prevalent in many basins in our country and even all over the world. The deformation simulation of positive inversion structures can deepen the understanding of the main controlling factors, identify the degree of fault inversion and help the exploration and development of oil and gas. In this paper, the discrete element numerical simulation method is used to study the effects of the presence or absence of detachment layer, the thickness of detachment layer, the strength of detachment layer, and the longitudinal depth of detachment layer on the deformation characteristics and deformation mechanism of folded thrust fault zones containing pre-existing rift traps, and we observe the reversal time of the pre-existing rifttrapped
bounding faults in the simulation results, as well as the final degree of reversal. The experimental results show that there is a regional extensive detachment layer in the upper part of the pre-existing rift, which transform the fold-thrust belt from a forward thrust imbricate structure to a more rheological crumple structure with the progress of extrusion. and the strata above the detachment layer slides along the detachment layer for a long distance. The regional extensive overburden detachment layer has a strong inhibitory effect on the inversion of the underlying pre-rift boundary fault. When the thickness of the regional extensive detachment layer is larger, the capability is weaker and the longitudinal depth is deeper, the inhibitory effect on the underlying pre-existing rift boundary faults is stronger, the inversion of the boundary fault occurs later and the final degree of inversion is smaller or even no inversion occurs. The gypsum layer of the Lower Triassic Jialingjiang-Leikoupo Formation in Sichuan Basin has a strong inhibitory effect on the activation of the underlying preexisting faults. The boundary fault of the underlying Deyang Anyue rift did not have obvious activation inversion under the extrusion of the Himalayan Movement, good preservation conditions of oil and gas are obtained.

Key words: Positive inversion structure, discrete element method, detachment layer, structural deformation, Deyang-Anyue rift