Characteristics And Evolution Of Major Faults In Western Hubei,Eastern Chongqing,Western Hunan And Western Hubei

West Hubei and east Chongqing and West Hunan and Hubei are located in the Midwest of Yangtze plate.They have experienced many stages of structural movements and their deformation differences are large.Marine oil and gas have been adjusted,transformed and even destroyed in many stages.Preservation has become the key to hydrocarbon accumulation in the study area,and fracture is an important factor restricting the differential preservation of oil and gas.Based on outcrop data,seismic data,analysis and test data and regional dynamic background data,guided by the theories of structural geometry,structural kinematics and seismic stratigraphy,this paper makes a detailed interpretation of main structural zone in the study area.In addition,the research on main fault systems and structural evolution analysis has been carried out,the main results are as follows.(1)There are two structural styles in the study area: basement involved type and caprock detachment type.The basement involved type is divided into compressional fault block,extensional fault block and basement thrust fold combination.The caprock detachment type is divided into normal fault combination and thrust fold combination.In addition,according to the characteristics and combination forms of folds and faults,there are back thrust block and hedge thrust block in compressional fault block,horst-graben structure in extensional fault block,large imbricated thrust zone in basement thrust fold combination,listric normal fault and rolling anticline in normal fault combination,and there are six kinds of structural elements in thrust fold combination,which are fault bend anticline,fault-propagation anticline,detachment anticline,triangular-zone structure,imbricate fan and duplex structure.(2)The study area can be divided into three second-order structural units: barrier folds of West Hubei and east Chongqing,trough folds of West Hunan and Hubei,and the Jiangnan-Xuefeng orogenic belt.Among them,barrier folds can be divided into Fangdoushan anticline belt,Shizhu anticline belt and Qiyueshan anticline belt;trough folds can be divided into Lichuan anticline belt,central anticline belt,Huaguoping anticline belt,Yidu-Hefeng anticline belt and Sangzhi-Shimen anticline belt.(3)There are 13 faults in the study area,which are Fangdoushan fault,Qiyueshan fault,jiutaishan fault,Jianshi fault,Chashan fault,Pengshui fault,Xuanen fault,Daping fault,Xianfeng fault,Hefeng Longshan fault,Moshi fault,yantangwan fault and Cili-Baojing fault from northwest to Southeast.On the plane,the strike of 13 faults is nearly parallel,and they are distributed from the southwest to the northeast as a whole.On the section,the formation time of the fault has periodicity,and the whole fault starts from the east and gradually transfers to the west.In addition,there are obvious differences in fault stress and fault growth index.(4)Based on the study of the shortening of the third-order structural units,it is considered that in the early Indosinian-Yanshan period,the Sangzhi-Shimen and Yidu-Hefeng area in the west of Hunan and Hubei are the most active,while the Shizhu area in the east of Chongqing and the west of Hubei is weak,and the intensity of the rest areas is basically the same.From the early Yanshan to the late Himalayan,the structural activities in Sangzhi-Shimen area and Yidu-Hefeng area are weak,and the intensity in other areas is basically the same.Since the late Himalayan,the third-order tectonic units have been shortened very little,which can be ignored.There is no large tectonic activity in this area,and the area is mainly affected by denudation.(5)Combined with the regional tectonic boundary,four seismic sections passing through the main faults are selected in the area from the study area,and the paleotectonic recovery is carried out,and then the tectonic evolution law of the study area is analyzed.The results show that the study area mainly experienced five stages of structural evolution,from early to late: Indosinian,early Yanshanian,middle Yanshanian,late Yanshanian to early Himalayan,late Himalayan to present.