Formation of large low shear velocity provinces through the decomposition of oxidized mantle

Wenzhong Wang (), Jiachao Liu (), Feng Zhu, Mingming Li, Susannah M. Dorfman, Jie Li and Zhongqing Wu ()
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Wenzhong Wang: University of Science and Technology of China
Jiachao Liu: Michigan State University
Feng Zhu: University of Michigan
Mingming Li: Arizona State University
Susannah M. Dorfman: Michigan State University
Jie Li: University of Michigan
Zhongqing Wu: University of Science and Technology of China

Nature Communications, 2021, vol. 12, issue 1, 1-10

Abstract: 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% MgSiO3–10 mol% Fe2O3 system, rather than forming a homogeneous single phase. The Fe3+-rich bridgmanite has substantially lower velocities and a higher VP/VS ratio than MgSiO3 bridgmanite under lowermost-mantle conditions. Our modeling shows that the enrichment of Fe3+-rich bridgmanite in a pyrolitic composition can explain the observed features of the LLSVPs. The presence of Fe3+-rich materials within LLSVPs may have profound effects on the deep reservoirs of redox-sensitive elements and their isotopes.

Date: 2021
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DOI: 10.1038/s41467-021-22185-1

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