后撤式逆冲推覆断层成因机制及物理模拟——以准噶尔盆地西北缘克-百断裂带为例

Genesis and Physical Modeling of Backward Propagation Thrust Fault:A Case Study of Ke-Bai Fault Belt in the Northwestern Margin,Junggar Basin

位于准噶尔盆地西北缘中段的克-百断裂带,晚二叠世以来发育了一系列后撤式逆冲断层。长期以来,关于克-百断裂带高角度逆冲断层的成因机制一直处于争论当中,后撤式逆冲断层的物理模拟在国内尚未见文献报道。论文通过地震解释研究了克-百断裂带的构造变形特征及其演化阶段;应用断层"活动性系数"理论,半定量地描述了挤压条件下断层"活动性系数"、摩擦系数与断层倾角之间的关系,证明了挤压条件下也能形成高角度逆断层;结合"造山楔"理论解释了后撤式逆冲断层的成因机制。研究认为,克-百断裂带后撤式逆冲断层是印支期、燕山期持续挤压和扎伊尔山隆升效应综合作用的产物:挤压过程中发生"泊松效应",随着断层倾角增大,断层面上的正压力迅速增大、"活动性系数"降低,当倾角增大到一个临界值后断层停止活动,形成高角度的逆断层;同时扎伊尔山隆升造成挤压应力上移,为断层的后撤奠定了基础。最后利用砂箱物理实验模拟了克-百断裂带后撤式逆冲断层的形成过程。

The Ke-Bai fault belt located in the middle segment of the northwestern margin of the Junggar Basin has developed a series of backward propagation thrust faults since the Late Permian.The genesis of the high angle thrust fault in the Ke-Bai fault belt has been a matter of debate for decades.This study focused on the structural deformation features and evolution of the Ke-Bai fault belt on the basis of seismic interpretation.Based on the activity coefficient theory,relationships among fault activity coefficient,fraction coefficient and dip angles were discussed semi-quantitatively.Formation of the high angle thrust faults in the compressional stress field was demonstrated theoretically.Then combed with the wedge theory,explanation of the genesis of backward propagation thrust fault was proposed.It is concluded that the backward propagation thrust fault in the Ke-Bai fault belt resulted from the continuous compression and the uplift of Zaire Mountain during Indosinian to Yanshanian periods.Due to the Passion's effect,the normal pressure increases rapidly with the increase of dip angle and the decrease of fault activity coefficient during the compressional process.The movement of fault stops when the dip angle reaches a critical value.The uplift of the Zaire Mountain triggered the upward movement of the compressional stress,and subsequently,the backward propagation thrust faults.Finally,the genesis of the backward propagation thrust faults was simulated by the sand box experiment on the basis of designed model.