柴达木盆地北缘走滑-冲断构造特征及其油气勘探思路

处于阿尔金左行走滑构造带东缘的柴北缘,过去一致认为是个前陆逆冲带,并对其逆冲构造特征作了大量的研究。通过本次的野外地质勘察和深部地震测线研究,证实柴达木盆地北缘的主要变形样式为走滑-挤压构造,具有挤压推覆特征的同时伴生有走滑构造,并且主要断层系统沿走向滑动的距离远大于沿倾向冲断推覆的距离,从而建立了柴北缘走滑-逆冲构造的地质模型;这对其地震解释有指导作用。从柴达木盆地的构造变形时间序列和演变特征从西向东依次扩展、构造活动从老变新,认为柴北缘的走滑-逆冲构造受阿尔金山大型走滑构造和祁连山剧烈的逆冲挤压构造共同控制。最后研究了柴北缘的走滑-逆冲构造特征对油气勘探的意义,加强勘探评价冷湖—南八仙走滑逆冲构造带的翼部断块圈闭和赛什腾山南缘逆冲推覆体下伏地层。

Strike-thrust structures and petroleum exploration in northern Qaidam Basin

The northern Qaidam Basin, located to the east of the Altyn Tagh sinistral strike-slip belt, has long been considered to be a foreland thrust belt. According to a field geological survey and seismic cross section interpretation, we demonstrate that the main deformational feature of the north Qaidam Basin is a strike-thrust structure. It combines the structural styles of both foreland compression and a lateral displacement parallel to strike. The strike displacement is much greater than that of thrust displacement in the same main fault system. Based on the geometry of deformation, we have established a structural model of strike-thrust deformation in northern Qaidam Basin, that can be used to guide seismic interpretations. The structural time sequence is that deformation in the west is older than that in the east. In terms of structural evolution , deformation progressed gradually from west to east. So, the strike-thrust structures were controlled by both Altyn Tagh strike-slip deformation and by Qilian Mountains contractioned (thrust) deformation. Combining the strike-thrust structures with petroleum pooling, we believe that emphasis should be put on exploring structural lateral wings to discover fault traps in the Lenghu-Nanbaxian strike-thrust belt, and attention should be paid to the Mesozoic formation under the nappe of the southern Saishiteng thrust belt.