城口–房县断裂带的构造变形分析

Analysis of Structural Deformation of the Chengkou-Fangxian Fault Zone

城口–房县断裂带位于上扬子板块北缘,以其为界可进一步将大巴山构造带划分为南大巴山弧形构造带(南大巴山)和北大巴山逆冲推覆构造带(北大巴山)。城口–房县断裂带不仅控制着该地区的岩浆活动和沉积作用,同时对大巴山的构造演化起到了重要的主导作用。综合大量的野外调查、构造解析和显微构造观察,对城口–房县断裂带进行了分段性的构造解析,厘定出城口–房县断裂带发育两条不同走滑性质的走滑断裂带,并追踪其展布范围。右行走滑断裂带自西向东贯穿城口–房县断裂带,与扬子板块相对华北板块的斜向俯冲碰撞有关;左行走滑断裂带发育于城口–房县断裂带东段,形成于陆内造山阶段,并改造了东段早期的右行走滑构造。在板块碰撞造山之前,早期的城口–房县断裂带处于伸展环境中呈线状分布。在陆内逆冲推覆过程中,由于东西两侧砥柱的阻碍作用,城口–房县断裂带发生弧形弯曲呈现SW向弧形展布。

The Chengkou-Fangxian fault zone is located in the northern margin of the Yangtze Block. The fault zone divided the Dabashan orogenic belt into two units：the South Dabashan orocline （i.e. the South Dabashan） and the North Dabashan thrust belt （i.e. the North Dabashan）. The Chengkou-Fangxian fault zone played a key role in regional magmatism and sedimentation, and the tectonic evolution of the Dabashan area as well. Based on detailed field investigations, structural analyses and microscopic observation, two strike-slip fault zones, which are characterized by its dextral and sinistral strike-slipping, respectively, were recognized along the Chengkou-Fangxian fault zone. The dextral strike-slip faulting affected the whole fault zone was resulted from the oblique collision between the Yangtze Block and the North China Block, and the sinistral strike-slip faulting, which involved only the eastern part of the fault zone, was related to intra-continental orogeny. In addition, the former was superposed and transformed by the latter. Before the collisional orogeny, the Chengkou-Fangxian fault zone was a linear fault, however, due to the thrusting of the intra-continental orogeny, the Chengkou–Fangxian fault zone was deformed into a SW-convex arcuate fault zone, which is likely resulted from the pinning of both of its ends.