Deformation of olivine at 5 GPa and 350–900 °C

Knowledge of the rheology of the upper mantle is important for understanding both subduction-related phenomena and mantle flow in general. Here we report the results of stress relaxation experiments on San Carlos olivine at pressures between 5.3 and 1.3 GPa and from 350 to 900 °C. At 5 GPa and 500 °C the deformation best follows a model governed by long-range resistance to movement of dislocations. The yield stress of olivine has been measured at low strain rates of 10−7 s−1. We conclude that the upper limit for the long-term yield stress of olivine at 500 °C is 68 + 180/−44 MPa.We observe significant weakening and infer an associated change in deformation mechanism in olivine between 500 and 730 °C. This change is coincident with the limit of the seismogenic layer and the greatest elastic thickness measurements in oceanic crust.