天山南北前陆盆地冲断带沉积砂体对构造逆冲作用响应动力学

通过对中西部前陆盆地冲断带垂直隆升高度与水平挤压缩短的分析,认为前陆冲断带的构造逆冲作用是一种综合作用,是分别由垂直方向的隆升力和水平方向的前展力组成的矢量合力,两种力的联合作用控制了冲断带的沉积充填特征。垂直隆升作用产生逆冲型断层,形成垂向运动位移量,使冲断带山体隆升、盆地沉降、产生可容纳空间。水平前展作用产生走滑型断层,形成水平滑动位移量,使山体前移、物源前进。由此,将天山南北前陆盆地冲断带古近纪—新近纪的构造逆冲作用划分为5个阶段,分别对应着3套粗粒沉积物与2套细粒沉积物。①古近系底部砂砾岩是早喜马拉雅运动初始期逆冲推覆的标志,同时也是以水平前展力为主阶段(垂直隆升力为辅联合作用)陆源碎屑沉积充填的产物;②新近系底部发育的砾质粗碎屑沉积体是中喜马拉雅运动初始期逆冲推覆重新活动的标志,是冲断负载初期以水平前展力为主构造逆冲作用的结果;③新近系顶部库车组/独山子组底部砾质粗碎屑沉积体发育在中喜马拉雅运动晚期,是基底回弹抬升后期、水平前展力作用下大量沉积物供给、砂体进积的产物。古近系与新近系的2套湖相泥岩沉积,是在垂直隆升力为主作用阶段,山体抬升导致山前挠曲沉降加剧,致使湖平面上升而出现广泛沉积的结果。

Kinetics of sedimentary process response to thrusting in the thrust belts of foreland basins in southern and northern Tianshan

A brief analysis of vertical uplifting height and horizontal shortening on the thrust belt in foreland basins of the central and western China reveals that there are two types of forces that controlled the deposition of thrusting belt,one is the horizontal progress force and the other is the vertical uplifting force.The vertical lifting force gave birth to thrust faults.The vertical displacement by the force resulted in the uplifting of mountains and lowering of basins the thrust faults and created accommodation.The horizontal progress force generated strike-slip faults.The horizontal displacement by the force pushed mountains and provenance forward.Based on this understanding,the thrusting during the Paleogene-Neogene in southern margin of Junggar and Kuqa foreland basins can be divided into 5 stages that correspond to three sets of coarse grain deposits and two sets of fine grain deposits respectively.Among them,the conglomerate at the bottom of the Palaeogene was the product of terrigenous clastic deposition in the stage dominated by horizontal progress force (together with auxiliary vertical uplifting force) and also marks the existence of a over-thrusting in the early Himalaya movement;the conglomeratic coarse-grained deposits at the bottom of the Neogene were the result of thrusting under the dominant horizontal progress force in the early thrusting loading period and also marks the renewal activity of over-thrusting during the early-middle Himalaya orogeny;and the conglomeratic coarse-grained deposits at the bottom of the Kuqa-Dushangzi Formation at the top of Neogene were formed during the middle-late Himalaya orogeny when the base rebound and provide large amount of sediments and caused sandbody progradation under horizontal progress force.While another two sets of Paleogene and Neogene lacustrine mudstone deposits were formed in a period with vertical uplifting force predominant when mountain uplifting caused piedmont flexural subsidence being enhanced and lake level rising.