MgSiO3 dominant perovskite is believed to be the most abundant constituent mineral in the Earth’s lower mantle. Generally minerals form solid solutions and their nature should affect on physical properties of minerals. In this paper, we will introduce our recent studies about incorporation mechanism of FeAlO3 component into MgSiO3 perovskite and its crystal chemistry.

The high-pressure phase relation of MnSiO3 was examined up to 85 GPa and 2600 K using a laser-heateddiamond-anvil cell combined with synchrotron radiation. MnSiO3 garnet decomposes into a mixture of MnO with a rock-salt structure (B1) + SiO2 stishovite at pressures higher than similar to 20 GPa and temperatures higher than similar to 1200 K. However, MnO (B1) + SiO2 stishovite further transforms to a perovskite structure with increasing pressure. The phase boundary between these structures is positive in the pressure-temperature diagram. The triple point of garnet, MnO + SiO2 and perovskite in the pressure-temperature diagram is similar to 20 CiPa and 1200 K. MnSiO3 perovskite is orthorhombic, and consistent with space group Pbnm, both at high pressure and high temperature and at high pressure and room temperature, but becomes amorphous during decompression. The refined cell parameters of MnSiO3 perovskite at 85 GPa and 2600 K are a = 4.616(2) angstrom, b = 4.653(2) angstrom, c = 6.574(3) angstrom, and V = 141.2(2) angstrom(3). The a/b ratio increases (approaches 1) with pressure and temperature, while the root 2a/c ratio remains nearly constant (<1). This indicates that the orthorhombic distortion decreases and the structure tends toward a tetragonal perovskite with increasing pressure and temperature.

We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K, corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm. With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO2 + perovskite via reactions with SiO2. Magnesite is not the only host phase for subducted carbon—solid CO2 also carries carbon in the lower mantle. Furthermore, CO2 itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for diamond formation in the lower mantle.