库车坳陷第三纪断层滑动分析与古构造应力恢复

TERTIARY FAULT-SLIP ANALYSIS AND PALEOSTRESS RECONSTRUCTION OF THE KUQA DEPRESSION, NORTH TARIM BASIN

研究构造应力场的时空变化对于认识和理解褶皱冲断带的构造变形过程和油气构造圈闭的最终定型具有重要意义。基于对库车坳陷内第三系和同时卷入变形的白垩系中发育断层的野外观测 ,采用断层滑动数据反演方法 ,对库车坳陷的第三纪构造古应力进行恢复。结果表明 :库车坳陷第三纪的构造应力方向在空间位置上变化不大 ,在时间上经历了从NNW—SSE向到NWW—SEE的转变 ,构造挤压变形经历了两个阶段 :即NNW—SSE向逆冲挤压变形和相对较晚的NWW—SEE向逆冲挤压变形。结合库车坳陷油气成藏期 ,第二阶段的构造挤压变形发生在库车组沉积期间 ,为坳陷内油气的聚集提供了良好的圈闭条件。文中还探讨了造成库车坳陷内挤压应力场的两种可能动力成因。

A study on spatio-temporal changes of tectonic paleostress is helpful to recognize and understand structural deformation of fold-and-thrust belt and final formation of structural trap of hydrocarbon accumulation. The observations and measures on many faults in the Tertiary as well as in the Cretaceous rocks in the Kuqa Depression, Tarim Basin, could help us to reconstruct Late Tertiary tectonic paleostress field by inversing a lot of fault-slip data. The inversion results combining with field observations showed that the direction of compressive stress underwent a change from NNW-SSE to NNW-SSE, and the Tertiary structural compression of the Kuqa Depression had two stages: NNW-SSE compressive deformation in the earlier stage and NWW-SEE compressive one in the later stage. Meanwhile, the results from varied structural belts indicated that the paleostresses had consisted each other. According to the period of hydrocarbon accumulation in the Kuqa Depression, we thought that the two stages of compressive deformation played a critical role in the final formation of structural trap, specially, the later stage of deformation supported a good situation for the trap. In addition, two possible causes of Tertiary compressive deformation were discussed in the paper.