库车坳陷脆性构造序列及其对构造古应力的指示

Brittle Structure Sequence in the Kuqa Depression and Its Implications to the Tectonic Paleostress

在对野外脆性构造(主要是节理和断层)大量观测的基础上,根据它们与应力的关系,讨论了库车坳陷白垩纪末期以来的古构造应力时空变化.结果表明,在库车坳陷脆性构造中,早期隆升作用形成的主要发育在中生界的NEESWW向系统节理被晚期同构造期的在中生界与上第三系均发育的NNWSSE向和NWSE向节理切割并改造,这是对区域上构造应力场在进入新近纪时从弱伸展变化到强烈挤压这一过程的响应.基于断层滑动分析的古应力反演结果显示,此时盆山边界处以近NS向伸展应力状态占主导,而坳陷内部则表现为近NS向和NWSE向挤压应力状态.说明在进入新近纪后,最大主应力(σ1)方向从垂向变成水平,应力场发生了转变.此后的天山快速垂向隆升是库车坳陷北缘和内部应力状态存在差异的原因.

In order to understand the time-space changes of the Cenozoic tectonic paleostress in the Kuqa depression, detailed field observations and measurements were carried out. Paleostress evolution history is discussed from the Late Cretaceous, according to the relationship between brittle structures and stresses. Their sequence relation is inferred from field investigations and the calculated results indicate that the early ENE-WSW systematic joints caused by regional uplifting were cut and reworked by late NNW-SSE and NW-SE systematic joints. This corresponds to the change of regional stresses from weak extension to strong compression since the beginning of the Neogene. Results of paleostress inversion based on large amounts of fault-slip data display a stress pattern with near N-S extension on the basin margin and NW-SE compression in the basin interior. So at the beginning of the Neogene, the stress field changed and the maximal principal stress σ1 switched from vertical to horizontal. The rapid vertical uplifting of the Tianshan Mountains might be responsible for the stress difference between the basin range and interior.