Orthorhombic perovskite phases observed in olivine, pyroxene and garnet at high pressures and temperatures

Abstract

Ferromagnesian silicate olivines, pyroxenes and garnets with Mg/(Mg + Fe)≳0.3 (molar) have been found to transform to high-pressure phases characterized by the orthorhombic perovskite structure when compressed to pressures above 250 kbar in a diamond-anvil press and heated to temperatures above 1,000°C with a YAG laser. The zero-pressure density of the perovskite phase of (Mg,Fe)SiO 3 is about 3–4% greater than that of the close-packed oxides, rocksalt plus stishovite. For (Mg,Fe) 2SiO 4 compounds, the perovskite plus rocksalt phase assemblage is 2–3% denser than the mixed oxides. The experimental synthesis of such high-density perovskite phases in olivine, pyroxene and garnet compounds suggests that (Mg,Fe)SiO 3-perovskite is the dominant mineral phase in the earth's lower mantle.