Three-dimensional Structural Modeling In Front Of Micang Mountain In Northeastern Sichuan

The Micangshan is located in the northeast of the Sichuan Basin,and the north is connected with the Qinling orogenic beltj and the Dabashan thrust belt is in the east,and the west is connected with the thrust belt of the Longmenshan.Many studies have been done on the structural style and kinematic characteristics of this area,due to the limitation of the quality of seismic data in front of Micangshan,the geometric pattern of structural deformation in front of Micangshan is controversial,and the kinematic process of its structural formation is not clear.Therefore,it is necessary to further determine the structural deformation characteristics of the front of Micangshan and carry out in-depth research on its kinematicsIn this paper,based on the latest two-dimensional seismic data and constrained by the surface survey data,the structural morphology of the deep and shallow parts is analyzed by using the theory of fault-related folds.On this basis,the forward modeling of structural geometric deformation is used to analyze the kinematics of the typical sections in the study area.At the same time,the rationality of the structural deformation style determined by this study is tested,and the genetic mechanism of the structural deformation characteristics in the front of the Micangshan is analyzed.Based on the above-mentioned studies,the balance cross section of the near east-west main sections of the front belt of Micangshan are restored,and the structural deformation rates of different spatial positions in the Micangshan tectonic belt are analyzed in different periods.Finally,by means of three-dimensional structural modeling,the spatial transverse distribution and combination of faults and folds in the front of Micangshan are analyzed,and the influence of deep and shallow faults on the whole geometric deformation of the front belt in the study area is discussed.The genetic mechanism of structural geometric deformation at different levels is discussedIn this paper,it is shown that the geometric morphology of the front of the Micangshan is a large and gentle monocline,and the structural morphology is a back-spreading fault-propagation fold with triangular shear in the fore-wing,and the deformation is mainly controlled by two detachments,namely,the Sinian mudstone detachment and the pre-Sinian detachment.Five imbricated thrust faults were developed in the late Sinian mudstone delamination in the late Yanshan period,and three large blind thrust faults superimposed northward in the pre-Sinian detachment in the Himalayan period.Two sections of the western and the middle section of the study area were simulated by forward modeling,the total nappe displacement was obtained to be 29km and 25km respectively.The restoration of equilibrium profile shows that the shortening rate of the study area from west to east decreases from 38%to 17.5%,indicating that the folding deformation is weakened.From the three-dimensional structural model,it can be concluded that the faults gradually decrease and disappear from west to east in transverse direction.With the weakening of structural deformation,folds gradually disappear,presenting as monoclinal structure.