塔里木盆地西北缘沙井子构造带断裂构造分析

Fault analysis on Shajingzi structural belt,NW margin of Tarim Basin,NW China

沙井子构造带位于塔里木盆地西北缘,是分隔阿瓦提凹陷和温宿凸起的边界断裂。它是塔里木盆地研究最薄弱的大型断裂构造带之一。根据系统、精细的地震资料解释,沙井子构造带存在3套断裂体系:深部楔状冲断构造、狭义沙井子断裂和浅部的伸张构造。深部楔状冲断构造形成于志留纪—泥盆纪,由北西倾向的主冲断层和南东倾向的反冲断层形成构造楔;构造楔主要由前寒武纪变质岩组成,冲断前锋楔入于寒武系中部,造成上覆地层向温宿凸起方向的急剧抬升。狭义的沙井子断裂,即通常所说的沙井子断裂,为一条高角度基底卷入型挤压走滑断裂,形成于二叠纪末—三叠纪初,错断了早期的深部冲断楔。浅部的伸展构造形成于第四纪早-中期,为一系列较小规模的正断层,沿狭义沙井子断裂呈右步雁列状排列,构成左行剪切张扭性断裂带。深部的楔状冲断构造和浅部的伸展构造是本次研究的新发现。

Shajingzi structural belt is a boundary structural beh between Awati sag and Wensu uplift at NW margin of Tarim Basin. It is one of the poorest studied large fault structural belts in Tarim Basin. On the basis of fine interpretation of seismic data, Shajingzi structural belt is consisted of 3 sets of fault systems： the deep-buried wedge-shipped thrust system,the narrowsense Shajingzi fault system and the extensional tectonics near the Earth surface. The deepburied wedge-shipped thrust structure was formed by the NW dipped fore-thrust fault and its SE dipped back thrust fault in Silurian-Devonian. The wedge is composed of Precambrian metamorphic rocks. The front of the wedge penetrated into the Cambrian caused the upper rocks lifting toward the northwest and forming a slope. The narrow sense Sahjingzi fault, i. e., the traditionally named Shajingzi fault is a basement-involved compressive strike-slip fault with high dip angle formed from latest Permian to beginning Triassic. It cut off the ancient thrust wedge. The extensional tectonics near the Earth surface was formed in Earl-Middle Quaternary. A series of normal faults arrange in right lateral en echelon along narrow sense Shajingzi fault, and constitute 2 sinistral tenso-shear normal fault zones. The deep buried thrust wedge and the Quaternary extensional tectonics are new discoveries of this paper.