The frictional sliding properties of antigorite gouge under hydrothermal conditions

As a weak mineral overlying subduction-zone faults, the widespread presence of antigorite can markedly affect subduction-zone dynamics. To better understand the mechanical properties of antigorite-bearing faults, we conducted frictional sliding experiments on antigorite under hydrothermal conditions. The experimental setup involved a constant confining pressure of 100 MPa, a low pore fluid pressure of 30 MPa, and temperatures ranging from 100 °C to 500 °C. We varied the axial loading rate between 0.04, 0.2, and 1.0 μm/s to examine the velocity dependence of the friction coefficient. The results showed that the friction coefficient of antigorite exhibited a significant temperature dependence. Between 100 °C and 400 °C, the friction coefficient decreased from 0.66 to 0.54 as the temperature increased. Above 400 °C, the friction coefficient increased, reaching 0.7. The velocity dependence of antigorite exhibited velocity strengthening ( a – b > 0) throughout the entire experimental temperature range (100 °C–500 °C). The impact of pore-fluid pressure on the frictional behavior of antigorite was also significant. Under low pore-fluid pressure (30 MPa), the frictional strength increases above 400 °C, associated with dehydration hardening. In contrast, at high pore fluid pressure, frictional weakening continues at elevated temperatures, indicating that pore fluid pressure plays a crucial role in regulating the frictional stability of antigorite. Our experimental results demonstrate that the pore fluid pressure plays a key role in regulating the temperature-dependent frictional behavior of antigorite, highlighting the need for further investigation under varying fluid pressure conditions. • Friction vs. Temperature : μ drops 0.66→0.54 (100–400 °C), then rises to 0.70 at 500 °C—weakening to strengthening. • Velocity Dependence : antigorite is velocity strengthening (a–b > 0) across 100–500 °C; no unstable slip observed. • Pore-fluid Pressure : at 30 MPa, friction strengthens above 400 °C via dehydration; at high P f , weakening persists. • Deformation Mechanics : brittle at 200 °C (grain-boundary sliding, microfractures) but plastic at 500 °C (basal dislocation glide). • Microstructural : at 200 °C, localized shear and grain-size reduction; at 500 °C, diffuse shear with slip along (001) planes.