Microstructure and influence of slickenside on faulting behavior developed in limestone

Abstract:

Fault rocks preserve the microstructures created by faulting. Slickenside is one of such microstructures, which is a smooth surface like a mirror. In this study, we try to clarify 1) the formation process of slickenside and 2) the influence of slickenside on faulting behavior. For these purpose, we observed the slickenside developed in limestone along Glarus thrust from micro- to nano- meter scale observations using FE-SEM, TEM and AFM. Moreover, we performed a series of experiments to simulate slickenside on Carrara marble using a rotary shear apparatus. The experimental conditions are normal stress: 1.0 – 5.0 MPa and at slip rate: 0.1 m/s.

The observations on natural slickenside reveal that 1) the slickenside was formed within the cataclastic layer, 2) the slickenside itself is a very thin layer (less than 100 nm thick), 3) the surface of the slickenside is composed of oblate nano-grains, and 4) it shows the self-affine roughness property. Through the experiments, we could reproduce the slickenside having the same microstructural characteristics described above as those in Glarus thrust. The experiments reveal that 1) the frictional coefficient decreases with increasing slip distance and normal stress and 2) the oblateness of nano-grains forming the slickenside surface tends to be larger with increasing normal stress. The microstructural observation of the recovered samples suggest that the formation process of the slickenside is same as that of tribofilm.