School of Earth and Space Sciences,Peking University
The Dabashan tectonic belt is a typical intracontinental orogenic belt in China, located at the transitional zone between the Qinling orogenic belt and the Sichuan Basin. It is the main distribution area for proven reserves of large and medium-sized oil and gas reservoirs in the Sichuan Basin. The study area has developed multiple sets of detachment layers, and the distribution of detachment layers controls the structural deformation. Previous studies have determined the main structural styles of the study area based on the geological outcrop data, 3D seismic data and other technical methods, but there is still a lack of quantitative analysis of the structural deformation process and Kinematics characteristics. This article uses the discrete element numerical simulation method to calculate the differences in structural styles displayed within the same time step using PFC2D software, and conducts discrete element single factor comparative simulation experiments to explore the differences in structural styles in multi detachment layer systems. The experimental results show that (1) The detachment layer plays a controlling role in the development of structures in the cross section. On the one hand, the number of faults in both the double detachment system and the multi detachment system is higher than that in the single detachment system. The introduction of detachment layers makes the structural development in the system more complex; On the other hand, from the analysis of the developed fault properties, it can be seen that as the number of detachment layers increases, the number of forward thrust faults in the system shows a gradual increase. The number of reverse thrust faults in the multi detachment layer system is less than the first two models, and is significantly less than the number of reverse thrust faults in the double detachment layer system. The middle detachment layer has an inhibitory effect on the formation of reverse thrust faults. (2) The introduction of detachment layers accelerates the vertical thrust velocity of faults, and the middle detachment layer plays a role in connecting the basement detachment layer and the upper detachment layer. The phenomenon of structural decoupling is common in the double detachment layer system, and the development of secondary faults and folds is the main feature in multi detachment layer systems. (3) The multi detachment system shows obvious characteristics of secondary folds and faults, which is more consistent with the profile of eastern Daba Mountains. The dual detachment system shows more structural decoupling characteristics, which is more consistent with the profile of western section.