关键词: 断层摩擦实验, Riedel剪切, S-C组构

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