Chemistry of Bridgmanite in the MgO–SiO2–Al2O3–Fe2O3–FeO system at 27 GPa and 1700–2300 K

Abstract Bridgmanite, with (Mg,Fe)SiO3 as the major component, is the most abundant mineral on Earth and is stable under lower mantle conditions. When incorporating trivalent cations (Al3+ and Fe3+), bridgmanite can form various components such as the oxygen vacancy ((Mg,Fe2+)(Al,Fe3+)O2.5) and A-site vacancy ((Al,Fe3+)2/3□1/3)SiO3, □ = vacancy) components in addition to the charge-coupled (Fe2O3, Al2O3, FeAlO3) components. These vacancy-bearing components potentially allow the storage of volatiles in the lower mantle and the modification of the viscosity and compressibility of the lower mantle. However, our understanding of these defect components has been limited due to the previous focus on relatively simple systems. This study determined the compositions of bridgmanite and its associated phases in the MgO–SiO2–Al2O3–Fe2O3–FeO system as a function of temperature (1700–2300 K) at a fixed pressure of 27 GPa, relevant for uppermost lower mantle conditions. Our results suggest the presence of oxygen vacancies in bridgmanite, implying that the Earth’s lower mantle may store water and noble gases. Furthermore, our results agree with geophysical observations indicating slab stagnation in the deep mantle.