Formation of large low shear velocity provinces through the decomposition of oxidized mantle.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33771990.
- Also identified by DOI 10.1038/s41467-021-22185-1 and PMC identifier 7997914.
- 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
Large Low Shear Velocity Provinces (LLSVPs) in the lowermost mantle are key to understanding the chemical composition and thermal structure of the deep Earth, but their origins have long been debated. Bridgmanite, the most abundant lower-mantle mineral, can incorporate extensive amounts of iron (Fe) with effects on various geophysical properties. Here our high-pressure experiments and ab initio calculations reveal that a ferric-iron-rich bridgmanite coexists with an Fe-poor bridgmanite in the 90 mol% MgSiO<sub>3</sub>-10 mol% Fe<sub>2</sub>O<sub>3</sub> system, rather than forming a homogeneous single phase. The Fe<sup>3+</sup>-rich bridgmanite has substantially lower velocities and a higher V<sub>P</sub>/V<sub>S</sub> ratio than MgSiO<sub>3</sub> bridgmanite under lowermost-mantle conditions. Our modeling shows that the enrichment of Fe<sup>3+</sup>-rich bridgmanite in a pyrolitic composition can explain the observed features of the LLSVPs. The presence of Fe<sup>3+</sup>-rich materials within LLSVPs may have profound effects on the deep reservoirs of redox-sensitive elements and their isotopes.