Deformation textures and mechanical behavior of a hydrated amorphous silica formed along an experimentally produced fault in chert

We conducted a series of friction experiments on chert at intermediate to high slip velocities (V = 0.87 - 104 mm/s) and at low normal stress (sigma(n) = 1.5 MPa) to better understand the process of fault weakening by silica-gel formation, as identified in previous friction experiments on quartz-rocks. Fault weakening in chert samples occurred in association with the formation of a 0.1-mm-thick fault gouge layer that contains a thin, foliated layer of fine-grained material and a cataclastically fragmented zone characterized by clast-matrix texture. MFT-IR and XRD analyses reveal that the fault gouge consists of a mixture of hydrated amorphous silica and quartz grains. The mechanical behavior of the fault gouge at a small magnitude of strain (gamma = 0.008), as examined independently of the friction experiments using a rheometer, is characterized by a negative dependence of shear stress on strain rate with a notable hysteresis behavior. Citation: Hayashi, N., and A. Tsutsumi (2010), Deformation textures and mechanical behavior of a hydrated amorphous silica formed along an experimentally produced fault in chert, Geophys. Res. Lett., 37, L12305, doi:10.1029/2010GL042943.