Structural Geometrics And Kinematics Of Eastern Margin Of Sichuan Basin

The eastern margin of Sichuan basin is located on transition zone position of trough folds in West Hubei and Hunan and the barrier folds in the eastern Sichuan basin,which is influenced by Dabashan tectonic belt in its north.The east border is Qiyueshan anticlinal belt and the west border is Fangdoushan anticlinal belt.The tectonic deformation of the study area is complicated and it has experienced multi-stage tectonic activity.And so far we cannot confirm structural style,the stages of tectonic evolution and formation mechanisms in study area.So this paper's goal is to research the key periods of geotectonic transformation,the structural geometry and3 D structure in different tectonic belts,kinematics and formation mechanisms and so on.On the basis analysis,the theory of fault-related folds etc,we want to get the models of geometry and kinematics,and research the formation mechanisms of different tectonic belts in study area by analysis of geo-physics,2D/3D seismic,well logging and drilling and field data etc.Now,we achieve the following results:(1)Through the analysis of geophysical data,we summarize: eastern Sichuan and western Hubei and Hunan area is a unified whole and basement detachment interface uplift form east to west,and basement detachment interface under Qiyueshan anticlinal belt is a ramp.In the middle Yangtze region there is a low velocity decollement in the depth of ~20 km.The Moho surface's depth from east to west deepens and the Moho surface under Xuefengshan tectonic belt uplifts and is leaped.And I infer that it's because of the deep mantle upwelling;(2)The tectonic deformation's characteristic is form east to west,form center to sides.Qiyueshan anticline(~ 140 Ma)begins to uplift and then Fangdoushan anticline uplift.And Fangdoushan anticline uplift form transition in middle part to the north and south.Based on the research about AFT in western Hubei and Hunan area and Wanxian synclinorium,regional unconformity's analysis,uplift and erdsion in study area etc,we can find that tectonic deformation is from Xuefengshan tectonicbelt,western Hubei and Hunan area to Chuandong area;(3)Structural deformation on basement detachment interface controls reginal tectonic uplift in study area.Deep detachment is gypsum-salt rock of Middle and Lower Cambrian;middle detachment is mud shale of Longmaxi Formation;shallow detachment is gypsum-salt rock of Jialingjiang Formation,and it protects shallow stratum deformation;(4)Fangdoushan anticline belt can be divided into three sections: in the sourth section,its main deformation is tectonic wedge in the deep part,and tectonic wedge's inside is duplex.There are huge back thrusts on Longmaxi Formation to surface;in the middle section,its main deformation is tectonic wedge in the deep part and duplex in the middle part;in the north section,its main deformation is duplex in the deep part and stacking tectonic wedges on Longmaxi Formation;(5)Qiyueshan anticline belt can be divided into two sections: in the south section,deep huge duplex controls overlying strata uplift,and we can find that the surface is Sinian Formation in the eastern Qiyueshan anticline belt;in the north section,its main deformation is duplex in the deep part,but its scale is smaller than north section,and there are two main different tendency thrust faults in the middle part;(6)In the Shizhu synclinorium,basement thrust faults control deformation of Jiannan anticline,and the huge back thrusts on Longmaxi Formation control deformation of Longjuba anticline.In Huanglianxia area,its main deformation is duplex in deep part and stacking tectonic wedges in the middle part;(7)In the middle Yangtze region(Hunan tectonic belt to east Sichuan),its tectonic deformation is ultra-large type tectonic wedge and it's movement is from east to west.So the main tectonic stress' direction is EW.And the SN tectonic stress is because that the south Dabashan tectonic belt thrusts southward.And the WE tectonic stress is from resist of Chuanzhong block;(8)In northern part of the study area(Jinanan anticline),the thickness of the soft layers is thicker than the southern part.So displacement from east to west more easilytransmits in north part.And this different displacement in different part of study area leads formation of hinge zone in the middle Qiyueshan tectonic belt and Fangdoushan tectonic belt.And hinge zone in the north Fangdoushan tectonic belt is because of thrust from the south Dabashan tectonic belt.