The strength of Mg(0.9)Fe(0.1)SiO3 perovskite at high pressure and temperature.

Abstract

The Earth's lower mantle consists mainly of (Mg,Fe)SiO3 perovskite and (Mg,Fe)O magnesiowüstite, with the perovskite taking up at least 70 per cent of the total volume. Although the rheology of olivine, the dominant upper-mantle mineral, has been extensively studied, knowledge about the rheological behaviour of perovskite is limited. Seismological studies indicate that slabs of subducting oceanic lithosphere are often deflected horizontally at the perovskite-forming depth, and changes in the Earth's shape and gravity field during glacial rebound indicate that viscosity increases in the lower part of the mantle. The rheological properties of the perovskite may be important in governing these phenomena. But (Mg,Fe)SiO3 perovskite is not stable at high temperatures under ambient pressure, and therefore mechanical tests on (Mg,Fe)SiO3 perovskite are difficult. Most rheological studies of perovskite have been performed on analogous materials, and the experimental data on (Mg,Fe)SiO3 perovskite are limited to strength measurements at room temperature in a diamond-anvil cell and microhardness tests at ambient conditions. Here we report results of strength and stress relaxation measurements of (Mg(0.9)Fe(0.1))SiO3 perovskite at high pressure and temperature. Compared with the transition-zone mineral ringwoodite at the same pressure and temperature, we found that perovskite is weaker at room temperature, which is consistent with a previous diamond-anvil-cell experiment, but that perovskite is stronger than ringwoodite at high temperature.