Experimental evidence for silica-enriched Earth’s lower mantle with ferrous iron dominant bridgmanite

Izumi Mashino, Motohiko Murakami, Nobuyoshi Miyajima, Sylvain Petitgirard

Research output: Contribution to journalArticlepeer-review

Abstract

Determination of the chemical composition of the Earth’s mantle is of prime importance to understand the evolution, dynamics, and origin of the Earth. However, there is a lack of experimental data on sound velocity of iron-bearing Bridgmanite (Brd) under relevant high-pressure conditions of the whole mantle, which prevents constraints on the mineralogical model of the lower mantle. To uncover these issues, we have conducted sound-velocity measurement of iron-bearing Brd in a diamond-anvil cell (DAC) up to 124 GPa using Brillouin scattering spectroscopy. Here we show that the sound velocities of iron-bearing Brd throughout the whole pressure range of lower mantle exhibit an apparent linear reduction with the iron content. Our data fit remarkably with the seismic structure throughout the lower mantle with Fe2+-enriched Brd, indicating that the greater part of the lower mantle could be occupied by Fe2+-enriched Brd. Our lower-mantle model shows a distinctive Si-enriched composition with Mg/Si of 1.14 relative to the upper mantle (Mg/Si = 1.25), which implies that the mantle convection has been inefficient enough to chemically homogenize the Earth’s whole mantle.

Original languageEnglish
Pages (from-to)27899-27905
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number45
DOIs
Publication statusPublished - Nov 10 2020
Externally publishedYes

Keywords

  • Sound velocity
  • high pressure
  • iron spin-state change of bridgmanite
  • mineralogical model of the lower mantle

ASJC Scopus subject areas

  • General

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