Pressure stabilizes ferrous iron in bridgmanite under hydrous deep lower mantle conditions.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38773099.
- Also identified by DOI 10.1038/s41467-024-48665-8 and PMC identifier 11109188.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Earth's lower mantle is a potential water reservoir. The physical and chemical properties of the region are in part controlled by the Fe<sup>3+</sup>/ΣFe ratio and total iron content in bridgmanite. However, the water effect on the chemistry of bridgmanite remains unclear. We carry out laser-heated diamond anvil cell experiments under hydrous conditions and observe dominant Fe<sup>2+</sup> in bridgmanite (Mg, Fe)SiO<sub>3</sub> above 105 GPa under the normal geotherm conditions corresponding to depth > 2300 km, whereas Fe<sup>3+</sup>-rich bridgmanite is obtained at lower pressures. We further observe FeO in coexistence with hydrous NiAs-type SiO<sub>2</sub> under similar conditions, indicating that the stability of ferrous iron is a combined result of H<sub>2</sub>O effect and high pressure. The stability of ferrous iron in bridgmanite under hydrous conditions would provide an explanation for the nature of the low-shear-velocity anomalies in the deep lower mantle. In addition, entrainment from a hydrous dense layer may influence mantle plume dynamics and contribute to variations in the redox conditions of the mantle.