Shear deformation of dry polycrystalline olivine under deep upper mantle conditions using a rotational Drickamer apparatus (RDA)

Abstract

Shear deformation experiments on dry hot-pressed polycrystalline San Carlos olivine have been conducted at 4.9–9.6 GPa, 1300–1870 K and strain rates of 0.6–7.4 × 10 −5 s −1 using a rotational Drickamer apparatus (RDA) at a synchrotron facility. The stress was measured from the orientational dependence of lattice spacing for the (1 3 0), (1 3 1), (1 1 2), (1 2 2), (1 4 0) and (2 4 1) planes, as well as from the dislocation densities. Based on the mechanical and microstructural observations, we infer that deformation occurs by power-law creep involving dislocation glide and climb under high temperature conditions, whereas deformation is due to exponential creep through the Peierls mechanism at relatively low temperatures. In both regimes the strength of olivine at steady-state deformation at these pressures is much larger than those at lower pressures. The activation volumes V* is estimated to be ∼15–20 × 10 −6 m 3/mol for the power-law creep. Combined with the previous results under wet conditions, we present the recommended values of flow law parameters on olivine for power-law creep constrained by high-pressure deformation experiments.