Deformation of antigorite serpentinite at high temperature and pressure

Deformation experiments were conducted in a Griggs-type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures. Samples deformed at temperatures of 400–625 °C and pressures of 0.85–1.5 GPa experienced semi-brittle deformation resulting in localization on faults at 5% to 25% strain; samples deformed at 300 °C exhibited transitional behavior. The stresses measured for our samples are in good agreement with recent experiments conducted in the Deformation-DIA apparatus. However, our results indicate that steady state ductile flow is not achieved, in contrast with interpretations based on the Deformation-DIA experiments. Extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab–wedge decoupling inferred from geologic observations. Experiments conducted above the thermal stability of antigorite, at 700 °C and 1.5 GPa, show evidence for distributed deformation; this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement. In addition, samples exhibit velocity strengthening from 300 to 700 °C, a frictional behavior that inhibits earthquake nucleation.