Mechanical behaviors of intact antigorite as functions of temperature: Faulting, slow stick-slip and stable sliding

Abstract

Triaxial compression experiments on intact antigorite were performed under undrained conditions with a confining pressure of 100–400 MPa, temperature of 25–700 °C and strain rate of ∼1.5 × 10−6−10−5 s−1. We report a sequential transition in mechanical behavior from faulting to slow stick-slip behavior and then to stable sliding with increasing temperature. Syndeformational dehydration of antigorite at 100 MPa and 550–650 °C produces slow stick-slip, and the slip velocity and shear stress drop generally decrease with increasing temperature. At 100 MPa and 650 °C, the slip velocity and shear stress drop of slow stick-slip gradually decrease, implying a trend toward stable sliding, which might be related to a continuous increase in fluid pressure induced by the accumulation of fluid over time in the process of antigorite dehydration. Our results indicate that dehydration makes the sample weaker but more stable and does not cause embrittlement; therefore, an intermediate-depth earthquake in a subduction zone may be triggered by brittle deformation in strong peridotite surrounding dehydrating antigorite. Similar to the antigorite fault gouge previously studied, intact antigorite can also induce slow stick-slip under partial antigorite dehydration, indicating that slow earthquakes could be triggered in the mantle wedge of a hot subduction zone.