Phase relations of bridgmanite, the most abundant mineral in the Earth's lower mantle.

The knowledge of phase relations of constitutive minerals is essential to investigate the structure, dynamics and evolution of the Earth and planetary interiors. This paper reviews the phase relations of bridgmanite, the most abundant mineral in the Earth's lower mantle, with an ideal composition of MgSiO. Bridgmanite has an orthorhombic structure with larger dodecahedral A and smaller octahedral B cation sites. The A-sites can incorporate Mg, Fe, Fe, and Al, while the B-sites accommodate Si, Al and Fe. The incorporation of hydrogen and large cations like Ca is likely limited, although these issues are still debated. Al and Fe, respectively, can form the charge-coupled components, AlAlO and FeFeO occupying both A- and B-sites. When both Al and Fe are present, Al occupies B-sites, and Fe occupies A-sites, forming FeAlO. In systems with excess MgO, Al and Fe also form the oxygen vacancy components MgAlO□ and MgFeO□. The phase relationships of bridgmanite with coexisting phases are discussed as a function of pressure, temperature, and oxygen fugacity from the simple MgSiO system to the complex MgO-FeO-FeO-AlO-SiO system.