Brittle Structure Sequence in the Kuqa Depression and Its Implications to the Tectonic Paleostress
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摘要: 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NEE-SWW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NNW-SSE向和NW-SE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N-S向伸展应力状态占主导, 而坳陷内部则表现为近N-S向和NW-SE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.Abstract: 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.Resultsof 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.
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Key words:
- brittle structures /
- joint /
- fault /
- paleostress /
- Kuqa depression
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图 1 库车坳陷构造简图
Fig. 1. Simplified structural outline of the Kuqa depression, northern Tarim basin
图 2 库车坳陷野外观测点上节理走向玫瑰花图
Fig. 2. Rose diagrams of joint and shear fracture orientation at each site on the structural map of Kuqa depression
图 3 库车坳陷库车河地区脆性断层运动方向与古应力状态(断层滑动数据采用斯密特下半球投影)
Fig. 3. Fault-slip direction and calculated paleostress along the Kuqa river in Kuqa depression
图 4 库车坳陷主干地震剖面KC-Z90构造地质解释剖面图
Fig. 4. Interpretation profile of the KC-Z90 seismic line in the Kuqa depression
图 5 库车坳陷系统节理、剪切破裂方位与水平应力轴之间的关系
Fig. 5. Relationship between the orientation of systematic joint and shear fracture and horizontal principal stresses in the Kuqa depression
图 6 库车坳陷脆性构造变形序列及其对应的古应力方位
Fig. 6. Schematic illustration of sequence of brittle structures and the evolution of correspondent stress in the Kuqa depression
表 1 系统节理与共轭剪切破裂的序列关系及其可能的应力场状态
Table 1. Sequence of systematic joints and shear fractures and possible paleostress state they correspond to
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