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 degrees 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 degrees 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 degrees 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 degrees C, a frictional behavior that inhibits earthquake nucleation. (C) 2010 Elsevier B.V. All rights reserved.