Frictional properties of serpentine gouge under high pore-fluid pressure and low effective normal stress conditions

Abstract

Serpentine minerals exist pervasively near the subduction mantle wedge. Due to their distinct physical and chemical properties, they have the potential to significantly impact the frictional behavior and stability of subduction fault zones. Here we investigated the frictional properties of an antigorite-lizardite mixture gouge under hydrothermal conditions with an effective normal stress of 30 MPa, a pore fluid pressure of 100 MPa, and temperatures ranging from 100 °C to 500 °C. To explore the velocity dependence of frictional strength, the loading rate is switched between 0.04, 0.2, and 1.0 μm/s. The results show that the friction coefficient of the gouge decreases systematically with temperature, with values ranging from 0.75 to 0.36. The thermal weakening of the gouge friction can be attributed to enhanced intergranular pressure solution processes activated at the relatively high fluid pressure. Stable velocity-strengthening behavior was observed in most cases. However, velocity-weakening behavior, evidenced by sustained oscillation, was found at 300 °C and 400 °C at the slowest loading rate (0.04 μm/s), with a transition to velocity-strengthening behavior at higher loading rates. Our results further suggest that, under the high pore fluid pressure and temperature conditions characteristic of the subduction zone mantle wedge, the nucleation of unstable slip at low slip rates can decelerate as fault slip accelerates into the velocity-strengthening regime, ultimately terminating as a slow-slip event. These insights contribute to a better understanding of the processes underlying slow slip events in subduction zones.