Cenozoic Structural Deformation And Spatial Variation Of The Wensu Uplift And Its Northern Margin,Tarim Basin

Wensu Uplift and its northern margin is mainly developed four structural belts with distinct deformation characteristics,including Awate structural belt,Gumubiezi structural belt,Shenmuyuan structural belt and Wushixi structural belt,which is important part of the Cenozoic Southern Tian Shan Thrust Belt.This paper analyzes the 2D seismic reflection data,well drilling materials and field outcrops,four structural belts of Wensu Uplift and its northern margin taken as a whole group,the Cenozoic deformation characteristics of the Wensu uplift and its northern margin are studied systematically,and analyzes the spatial differences and the structural transformation between each structural belt of the study area,and the differential deformation mechanism and controlling factors of the Wensu uplift and its northern margin are discussed,the following conclusions are drawn:(1)The Awate structural belt shows the characteristics of stratified deformation style with the gypsum-salt bearing Kumugeliemu Group detachment layer as the boundary.The upper part is the salt diapir and related structures,while the lower part develops southward imbricate thrust system;the Shenmuyuan structural belt includes southward imbricate thrust system and the duplex structural system under the Wushi sag;the Wushixi structural belt is a low-angle basement involved imbricate thrust system;the Gumubiezi structural belt can be divided into east and west segments.The east segment is composed of the Gumubiezi fault,Gumubiezi anticline and Wensubei fault,the west segment is composed of the Wensubei fault and anticlines are formed by the en echelon arrangement.(2)From the Awate structural belt,Shenmuyuan structural belt to Wushixi structural belt,the deformation affected by the detachment layer becomes weaker.Structural deformation controlled by the gypsum-salt bearing layer of the Kumugeliemu Group in the Awate structural belt,the duplex structure takes the gypsum bearing mudstone in the Jidike Formation as the roof thrust in the Wushi sag in the southern Shenmuyuan structural belt,and there is no thrust system affected by the detachment layer in the Wushixi structural belt.The adjustment of the three structural belts is mainly through the structural transformation between structural belts through large strike-slip fault and vertical(gradual change)transformation.(3)Gumubiezi Fault(GF)in the Gumubiezi structural belt starts to move as a decollement along the Neogene gypsum-bearing mudstone layer in the Jidike Formation at the Early Quaternary and breaks southward to the ground surface at the northern margin of the Wensu Uplift and formed Gumubiezi anticline on the hanging wall of the GF.The displacement of the GF decreases gradually from 1.21 km in the east C1?C? transect to 0.39 km in the west HH? transect,and the GF completely disappears in the west of the Gumubiezi anticline.One part of the displacement in the GF is converted into the forward thrust,and another part is absorbed by the Gumubiezi anticline.The formation of the GF is related to the gypsum-bearing mudstone layer in the Jidike Formation and existence of the Wensu Uplift,the lateral variation of deformation style from east to west is controlled by the difference of gypsum-bearing mudstone layer in the Jidike Formation.Gypsum-bearing mudstone layer in the Jidike Formation is thick in the east,where deformation of the duplex structure in the north of the transect transfers to the basin by gypsum-bearing mudstone layer.However,the thickness of Gypsum-bearing mudstone layer decreases shortly in the west part of the Gmubiezi structural belt,which results in deformation of the duplex structure weaker transformation of gypsum-bearing mudstone layer to the basin.However,the gypsumbearing mudstone is not developed in the II? transect in the west,the deformation in the west cannot be transformed along the Jidike Formation into the basin,the deep thrust fault breaks to the surface and the GF disappeared completely.The displacement of the GF to the west eventually disappeared because of the lateral ramp acting as the transitional fault.(4)Balance the 6 cross sections of the study area,the shortening amount and shortening ratio of each evolution stage were obtained.It shows that the shortening amount and shortening ratio of the Wensu Uplift and its northern margin decreases gradually from east to west.Cenozoic structural evolution can be divided into three stages,namely the early Miocene(? 23 Ma),the early Pliocene(? 5.2 Ma)and the early Quaternary(? 2.6 Ma),in which the deformation in the early Pliocene(? 5.2 Ma)was the strongest one,and the average shortening of the 6 balanced cross sections are 11.30 km;in the second place was 5.53 km since the early Quaternary(? 2.6 Ma).The structural deformation of the Wensu uplift and its northern margin is influenced by two factors:(1)Wensu paleo uplift and pre-existing faults that controlling Wensu paleouplift;(2)detachment layer and syn-thrusting sedimentation.