The roles of quartz and water in controlling unstable slip in phyllosilicate-rich megathrust fault gouges

摘要: A recent microphysical model for the steady-state frictional behaviour of wet illite/quartz gouges in subduction megathrust settings predicts that velocity-weakening seismogenic zone results from a competition between shear-induced dilatation and compaction involving water-assisted, thermally activated deformation (pressure solution) quartz clasts. While this is supported by experimental data, proof water are requirement lacking. Here, we report on shearing experiments water-saturated (near-)pure illite dry 65/35 gouges, deformed at P-T conditions near those situ depths along megathrusts. We used low sliding velocities relevant to earthquake nucleation slow slip events (1 100 μm/s). Previous under same documented three regimes stability, with velocity-strengthening 150°C 250°C 400°C 500°C, 400°C. In present study, gouge exhibited similar three-regime behaviour, but velocity-neutral rather than intermediate temperatures. Dry all temperatures investigated. These confirm key process support existing model. The implication seismogenesis occurs where creep fast enough moderate ‘brittle’ remain subcritical porosity values too allow ductile shear