Cited by 1,134High-pressure geophysics and materialsGeological and Geochemical AnalysisAstro and Planetary Science

The Redox State of Earth's Mantle

Frost, Daniel J., McCammon, Catherine A.·2008·Annual Review of Earth and Planetary Sciences

Abstract

Oxygen thermobarometry measurements on spinel peridotite rocks indicate that the oxygen fugacity at the top of the upper mantle falls within ±2 log units of the fayalite-magnetite-quartz (FMQ) oxygen buffer. Measurements on garnet peridotites from cratonic lithosphere reveal a general decrease in fo 2 with depth, which appears to result principally from the effect of pressure on the controlling Fe 3+/Fe 2+ equilibria. Modeling of experimental data indicates that at approximately 8 GPa, mantle fo 2 will be 5 log units below FMQ and at a level where Ni-Fe metal becomes stable. Fe-Ni alloy and an Fe 2 O 3-garnet component will be formed as a result of the disproportionation of FeO, which is experimentally demonstrated through observations of high Fe 3+/ΣFe ratios in minerals in equilibrium with metallic Fe. In the lower mantle, the favorable coupled substitution of Al and Fe 3+ into (Fe,Mg)SiO 3 perovskite results in very high perovskite Fe 3+/ΣFe ratios in equilibrium with metallic Fe. As a result, the lower mantle should contain approximately 1 weight% metallic Fe formed through FeO disproportionation, if the bulk oxygen content is the same as the upper mantle. Loss of disproportionated metallic Fe from the lower mantle during core formation could explain the higher Fe 3+/ΣFe ratio of the present-day upper mantle when compared to that expected during core formation. The influence of pressure on mantle fo 2 has important implications for the speciation of C-O-H-S volatile phases in Earth today and during its early evolution.

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Crossref · 10.1146/annurev.earth.36.031207.124322

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  • The Hadean atmosphere and mantle were probably initially highly reducing, before subsequent oxidation either by hydrogen escape or disproportionation of mantle FeO accompanied by Fe loss to the core.

    “Therefore, the Hadean atmosphere and mantle were probably initially highly reducing, before subsequent oxidation either by hydrogen escape (29) or disproportionation of mantle FeO accompanied by Fe loss to the core (30, 31).”

    From The Archean atmosphere (2020) · cites this paper as [30]

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Authors
Frost, D. J., & McCammon, C. A.
Affiliations
University of Bayreuth (DE)
Venue
Annual Review of Earth and Planetary Sciences
Published
2008-05-01
Volume
36
Issue
1
Pages
389-420
ISSN
  • 0084-6597 (ISSN-L)
  • 1545-4495
OpenAlex
W2171968174
Cited by
1,134
References
124
Citations by year
2026: 65 · 2025: 91 · 2024: 72 · 2023: 67 · 2022: 78 · 2021: 93 · 2020: 84 · 2019: 77 · 2018: 81 · 2017: 70 · 2016: 64 · 2015: 55 · 2014: 56 · 2013: 61 · 2012: 29
FWCI
5.72
Type
journal article
Language
en
Open access
closed
Locations
Annual Review of Earth and Planetary Sciences (publishedVersion)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › High-pressure geophysics and materials
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
Keywords
mantle redox state, oxygen fugacity, spinel peridotite, garnet peridotite, metallic iron, perovskite, core formation, cratonic lithosphere, early Earth evolution

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