华北沧东断裂的构造特征

STRUCTURAL CHARACTERS OF THE CANGDONG FAULT IN NORTH CHINA

地质和地球物理资料表明 ,沧东断裂为发育于上地壳的上陡下缓的铲状断裂 ,断面于 10km深处的上地壳底部变为近水平的拆离滑脱面。沧东断裂经历了中、新生代两个裂陷旋回 ,开始形成于晚侏罗世 ,此时为正断裂性质 ,早白垩世末期的燕山运动使断裂反转为逆断裂 ,并有一定的左旋走滑 ,形成正花状构造。早第三纪始新世时在中生代断裂的基础上改造成为正断裂 ,控制了黄骅坳陷下第三系的分布。早第三纪为断裂主要活动时期 ,塑造了现今沧东断裂的主要形态 ,断裂不同区段的产状、发育历史和活动强度表现出鲜明的分段性。晚第三纪以来断裂活动微弱。从浅层地震勘探结果看 ,沧东断裂晚更新世以来基本不活动 ,不是活动断裂。

The latest geological and geophysical data show that the Cangdong fault is a listric fault in the upper crust. The plane of the fault becomes a detachment plane at the 10km depth in the crust. The Cangdong fault has undergone two rifting processes in Mesozoic and Cenozoic time. It formed in late Jurassic as a normal fault, and became a thrust fault by the end of early Cretaceous. It was a normal fault in Eocene, evidenced by the Mesozoic structure, and controlled the distribution of stratum of early Tertiary. Palaeogene is the major active period for the Cangdong fault, the major character of the fault formed in this period. The faults occurrence, development history and activity are different in different segments. The activity of the fault has been weak since Neogene. Based on the shallow seismic exploration, it is suggested that the Cangdong fault is not active since later Pleistocene on the whole and has little seismicity.