Abstract: Experiment on frictional sliding of simulated fault gouge is of great significance to the understanding of earthquake nucleation and natural shear zone structures. The present paper deals with deformational structure of simulated gabbro fault gouge and its origin,for the purpose of understanding fault activity in deep crust. The experiment also shows that various shear structures are well developed in the simulated fault gouge. Among them,the boundary shear,R₁ shear,Y shear and T gash are relatively well developed,but R₂,P and X shears are scarcely observed. R₁ shear has an angle of about 11°to the boundary surface,indicating the formation of a set of Coulomb fracture during the process of shear deformation. Observation of the thin sections shows that the density of R₁ shear increases with increasing normal stress,while under the same normal stress condition the density of R₁ shear increases with increasing temperature. Microstructural observations show that under temperature condition of 200℃the fault gouge is dominated by brittle deformation,involving grain crushing,cataclastic flow by shear comminution,and the banded alignment of dark colored minerals such as biotite and pyroxene along the shear plane. Between the temperature of about 200～400℃,preferred orientation of felsic minerals is gradually formed,defining mylonite like foliation. Above 500℃,the densely distributed R₁ shears occurr in the strongly deformed region,and they tend to coalesce with Y shears rather than to cut through the gouge layer,leading to the well development of Y shears. In these high temperature conditions,plagioclase begins to deform plastically,and the foliation defined by felsic minerals separates from that defined by dark-colored minerals,resulting in a typical S-C fabric.

Key words: frictional experiment, Riedel shear, S-C fabric

摘要： 模拟断层泥的摩擦实验对地震的成核及断层带变形组构的研究具有重要意义。文中对辉长岩摩擦实验中的断层泥变形组构及形成机理进行了研究,以期从实验室角度来理解地壳深部断层活动的性质和特点。断层泥剪切组构中的边界剪切带,R₁,Y剪切面比较发育,T裂隙次之;R₂,P,X剪切面不发育。R₁面与边界面的夹角较小,平均在11°左右,为单剪变形过程中达到破裂极限状态时形成的1组库仑破裂面。分析表明R₁面密度随正应力的增加而明显增高。而在相同的正应力下,随温度的增高,R₁面的密度也有增加的趋势。当温度高于500℃时,断层带内的斜长石出现塑性变形特征,R₁剪切面与矿物的压性面理组成典型的S-C组构。

关键词: 断层摩擦实验, Riedel剪切, S-C组构