塔里木盆地皮羌断裂晚期活动ESR年代学证据及其地质意义

皮羌断裂是塔里木盆地北缘柯坪隆起上北西方向的走滑断裂。该断裂在卫星图片上整体表现出以左行走滑为主,南段则为局部右行走滑的特征。位于盆地周缘隆起的皮羌断裂与盆地内巴楚隆起色力布亚断裂具有良好空间对接关系,因此皮羌断裂活动的年代学证据对于塔里木盆地的晚期构造变形研究具有重要意义。野外调查表明皮羌断裂将柯坪隆起古生界错断,并通过拖曳作用牵引至地表。该地区古生界奥陶系主要以碳酸盐岩为主,地层内部经断裂错断以及后期流体结晶充填等综合作用,发育大型的方解石脉体。通过断裂带内方解石脉体的ESR电子自旋共振年龄的测定,发现皮羌断裂在晚期可记录的年龄为(6.2～6.6)×10⁴ a,而中段可记录的年龄为(358.3±35.0)×10⁴ a,南、北段相近的年代学数据说明在晚期皮羌断裂具有同步活动的特点。通过对皮羌断裂方解石脉年代差异的成因分析,认为柯坪隆起在南西向推覆作用之后,仍存在有原地体垂向隆升的可能,而这种隆升作用也是皮羌断裂南、北两端差异调节的结果。

Chronology evidence of ESR dating for the late movements of the Piqiang fault in the Tarim Basin and its geological implication

The Piqiang fault is a NW-trending strike-slip fault in the Keping uplift on the north margin of Tarim Basin.Satellite images of the fault show a left-lateral strike-slip faulting structure with local right-lateral characteristics in the south.The Piqiang fault and Selibu fault on the Bachu uplift in the basin shows well spatial matching relationship.Therefore,chronology evidence of ESR dating of the Piqiang fault bears great significance to the study of late deformation of Tarim Basin.Field surveys shows that the fault offset the Paleozoic in the Keping uplift and dragged it to the surface.The Ordovician in the area is dominated by carbonates and contains well-developed large calcite veins due to faulting and late fluid filling and crystallization.The dating of calcite veins in the fault belt indicates that the age recorded by the Piqiang fault at late stage is 62-66 ka,and that recorded by the middle part of the fault is 3 583?350 ka.The similar chronological age data of the southern and northern parts shows that the Piqiang fault has the characteristics of synchronous activity during the later period.Based on the genetic analysis of the big age differences of the calcite veins in the Piqiang fault,it is suggested that the Keping uplift still possibly experienced vertical uplifting even after overthrusting of Keping Uplift in SW direction.The vertical uplifting in turn is the result of differential modification at the south and north ends of the Piqiang fault.