The Effect of Wedge Structure on Displacement Subduction of Piedmont Thrust Structure:A Case Study of the Southern Margin of Junggar Basin

The foreland thrusting belts in the southern margin of Junggar Basin,lying between the stable Junggar craton and rejuvenated Tianshan orogen,is the product of long distance effect of collision between India plate and Eurasia plate in the Cenozoic,and also the directive result from the Tibet plateau uplifting and pushing toward north.The structure on one side of the craton tended to be stable after the foreland fold and thrust belts absorbed the thrust structural displacement resulted from orogen.The southern margin of Junggar basin shares similar geological characteristic as many other foreland thrusting belts in the world.Through analyses of fine geometry and kinematics of structural geology in south Junggar basin,it is found that the unique wedge structure is one of major approaches to absorb thrust displacement within the foreland thrust faulting zone and controls the scope of thrust distribution and deformation style.The structural deformation in the basin is dominated by northward overthrusting of the Tianshan orogenic belt in south,but most displacement was consumed by backward movement of the wedge structure.During northward expansion of the wedges along the Jurassic Xishanyao Formation coal seam in the deep foreland close to the Qigu-Kalazha-Jichang structural zone in north Tianshan Mts,part of displacement was absorbed southward along overthrusting layer at top of structural wedge and cut overlying strata to form the first row of anticline zone.And part of displacement propagated northward and deformed,triggering folding deformation at faulted slope and forming the Huo-Ma-Tu structural zone(the second row) and Anjihai-Hutubi the anticline zone(the third row).Within the Cenozoic of the second and third structural zones of the southern margin of Junggar Basin developed many small structural wedges.These superimposed wedges have limited horizontal extension,and this adds much difficulty in complexity of structural deformation and identification of structural traps.