逆冲-走滑作用叠加的复合构造变形机制砂箱模拟研究:以张家口-蓬莱断裂带渤海段为例

Sandbox modeling on the reworking of strike-slip faulting from pre-existing thrusts: A case study of Zhangjiakou-Penglai Fault Zone in Bohai area

  • 摘要: 逆冲构造体受走滑作用影响形成新的复合构造体系在自然界中较为常见。新生代以来张家口-蓬莱断裂带渤海段的左旋走滑运动,改造了渤海湾盆地内燕山期挤压运动形成的逆冲构造。北西向的张家口-蓬莱断裂带渤海段受新生代以来太平洋板块俯冲驱动,与共轭的北东向郯庐断裂带共同控制了渤海湾盆地现今的构造样式,同时又是地震多发区和油气聚集区。本文通过砂箱模拟实验,研究不同走滑速率不同基底强度条件下,逆冲推覆构造受走滑作用改造的复合构造演化机制。实验结果显示,在挤压背景下,实验模型中先产生一系列的逆冲断层,形成逆冲推覆构造和冲起构造;叠加走滑作用后,走滑断层切割先存逆冲断层,具有明显的负花状构造特征。剖面上看,走滑速率越大,则断层数量越多,断层断距更大,花状构造更为复杂。在局部塑性基底模型中,无叠加的走滑构造区可形成断陷。结合研究区构造演化过程,模拟结果与张家口-蓬莱断裂带渤海段构造演化过程具有一定相似性,尤其沙北断裂、沙东断裂内部花状构造发育最为典型。走滑断裂对构造圈闭具有一定的控制作用,本模型可对逆冲叠加走滑复合区域的构造演变及动力机制分析提供参考和借鉴。

     

    Abstract: It is common in nature for thrust structures to form new composite structural systems under the influence of strike-slip faulting. Since the Cenozoic, the sinistral strike-slip movement of the Zhangjiakou-Penglai fault zone in Bohai basin altered the pre-existed Yanshanian thrust structure. Driven by the subduction of the Pacific Plate since the Cenozoic, the NW-trending Zhangjiakou-Penglai fault zone fault zone co-worked with the conjugate NE-trending Tancheng-Lujiang fault zone and established the modern tectonic pattern of the Bohai Bay Basin. This area is an earthquake-prone area and also an oil-gas accumulation area. To understand the mechanism of strike-slip faulting from pre-existing thrusts, we conducted sandbox modeling with various strike-slip rates and basement rigidity setting. Results show a series of thrust faults forming thrust imbricate fan and pop-up structures under compression. After the superposition of thrusting by strike-slip motion, some strike-slip faults were formed and they cut through pre-existing thrusts, presenting a flower structure. Seen in the cross-section, the larger the strike-slip rate, the more faults, the larger the fault spacing, and the more complex flower structure. In the local plastic basement model, the strike-slip zone without superposition can form a fault depression. Combined with the tectonic evolution process of the study area, the modeled results showed a similar pattern of the tectonic pattern of the Zhangjiakou-Penglai fault zone, especially those of the flower structures in the Shabei fault and Shadong fault. Therefore, the strike-slip fault played a role in controlling the tectonic trap. This study provided a reference for understanding the dynamic mechanism of tectonic superposition of strike-slip faulting and thrusting.

     

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