Tectonic Evolution And Genetic Mechanism Of Western Hubei And Eastern Chongqing Area

Since Precambrian,Western Hubei and Eastern Chongqing area has been influenced by plate tectonism and intracontinental orogeny for a long time,which results in great differences between deep and shallow structures.On the basis of the previous geological mapping and surface geological structure research,it is of great significance for the next step of oil and gas exploration to use new seismic data to analyze the deep structure and establish a reasonable structural model.Based on the theory of fault related folds,this study redefines the structural units of the study area by means of the combination of shallow large section and seismic section analysis,and carries out the study of structural geometry and kinematics.Finally,through structural physical simulation test,we discuss the structural evolution and deformation mechanism of the study area since the Indosinian period.The main achievements of this paper are as follows:(1)Through the combination of shallow geological large section and seismic line interpretation,the tectonic units of the whole area have been redefined.The newly divided tectonic units can be divided into Lichuan structural belt,Enshi structural belt,Xuanen structural belt,Nanbeizhen structural belt,Sangzhi-Shimen structural belt and Xuefeng thrust belt from northwest to Southeast.(2)The structural characteristics of the Western Hubei-Eastern Chongqing area are stratified vertically.The basement structural layer is mainly composed of duplexes formed by basement thrust sheet.The lower structural layer is controlled by the lower Cambrian detachment and developed with fault-bend fold and fault-propagation fold.The deformation of middle-upper structural layer is weaker than that of lower structural layer,which is mainly controlled by shale of Longmaxi Formation of Lower Silurian,forming fault-propagation fold.(3)The study area is mainly affected by Yanshan episodic tectonic movement.Its deformation stage can be divided into five stages: 1)before 201 Ma,it's sedimentary construction period;2)from Late Jurassic to Early Cretaceous(201Ma-145Ma),it is the formation period of Sangzhi Shimen structural belt,nannanzhen structural belt and Xuanen structural belt in turn;3)from Early Cretaceous to Middle Late Cretaceous(145Ma-100Ma),Enshi structural belt and Lichuan structural belt began to uplift;4)form Middle Cretaceous to Late Cretaceous(100 Ma-75 Ma),it was the rapid uplift period of the whole western HubeiEastern Chongqing area;5)after Paleogene(65 Ma-32 Ma),the structural style of the Western Hubei and Eastern Chongqing region was basically finalized.(4)The overall deformation of the study area is realized on the premise that the form of basement detachment changes.Since Yanshanian,under the compression stress from the southeast,the deep basement detachment layers have been connected with each other in the longitudinal direction,gradually raised,making the dip angle(?)of the detachment gradually increased.Thanks to that,with the change of the overlying strata,the wedge top angle(?)will become smaller,forming the present pattern of large uplift in the south east side and small uplift in the north west side.Laterally,the study area is limited by Qinling-Dabashan structural belt.Under the action of multi-stage compressional stress with different directions,it has formed the geological form of superimposition of folds in different directions in many periods.