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通过对北京密云北石城断裂带的野外和室内工作,该断裂带的断层岩可分为四种类型:碎裂岩类、糜棱岩类、假熔岩和断层泥。它们具有不同的矿物学、形变和组构特征,分别代表不同的成因机制。假熔岩和碎裂岩类断层岩的存在,可作为古地震事件的可能证据。前者是地震断层运动在断层面上摩擦增温,引起围岩中矿物的选择性熔化形成的。在该断裂带中可能发生不止一次的古地震事件。断层岩特征和产状表明,该断裂带经历了两种不同力学性质的运动,早期为韧性剪切;晚期为脆性破裂,并伴有地震发生。
Through the field and indoor work on the Beijing-Beiyu Beicheng fault zone, the fault rocks in the fault zone can be divided into four types: cataclasites, mylonites, fake lava and fault mud. They have different mineralogy, deformation and structural features, representing different genetic mechanisms. The existence of fissured rocks of fossil lavas and cataclasites can be used as evidence of paleoearthquakes. The former is caused by the frictional warming of the fault movement on the fault plane and the selective melting of minerals in the surrounding rock. More than one episode of paleo-earthquake could occur in the fault zone. The characteristics and occurrence of fault rocks show that the fault has undergone two kinds of movement with different mechanical properties, ductile shearing in early stage and brittle fracture in the late stage accompanied by the occurrence of an earthquake.