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Abstract As the reaction product of subducted water and the iron core, FeO2 with more oxygen than hematite (Fe2O3) has been recently recognized as an important component in the D” layer just above the Earth's core-mantle boundary. Here, we report a new oxygen-excess phase (Mg, Fe)2O3+δ (0 < δ < 1, denoted as “OE-phase”). It forms at pressures greater than 40gigapascals when (Mg, Fe)-bearing hydrous materials are heated over 1,500 kelvin. The OE-phase is fully recoverable to ambient conditions for ex-situ investigation using transmission electron microscopy, which indicates that the OE-phase contains ferric iron (Fe3+) as in Fe2O3 but holds excess oxygen through interactions between oxygen atoms. The new OE-phase provides strong evidence that H2O has extraordinary oxidation power at high pressure. Unlike the formation of pyrite-type FeO2Hx which usually requires saturated water, the OE-phase can be formed with under-saturated water at mid-mantle conditions, and is expected to be more ubiquitous at depths greater than 1,000 km in Earth's mantle. The emergence of oxygen-excess reservoirs out of primordial and subducted (Mg, Fe)-bearing hydrous materials may revise our view on the deep-mantle redox chemistry.
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Experimental Constraints on the Fate of Subducted Sedimentary Nitrogen in the Reduced Mantle
Key Points Subducted N‐bearing silicates and fluids react with Fe or FeS to form different products at high P ‐ T conditions Stability of Fe‐LEs to 35 GPa and 1600 K is Fe‐O > Fe‐N > Fe‐S > Fe‐C, explaining the distribution of nitrides in diamonds The recycling efficiency of subducted sedimentary N is strongly related to the availability of the metallic Fe of the reduced mantle
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- PAR ID:
- 10451655
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 127
- Issue:
- 12
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Deep carbon cycle is crucial for mantle dynamics and maintaining Earth’s habitability. Recycled carbonates are a strong oxidant in mantle carbon-iron redox reactions, leading to the formation of highly oxidized mantle domains and deep carbon storage. Here we report high Fe3+/∑Fe values in Cenozoic intraplate basalts from eastern China, which are correlated with geochemical and isotopic compositions that point to a common role of carbonated melt with recycled carbonate signatures. We propose that the source of these highly oxidized basalts has been oxidized by carbonated melts derived from the stagnant subducted slab in the mantle transition zone. Diamonds formed during the carbon-iron redox reaction were separated from the melt due to density differences. This would leave a large amount of carbon (about four times of preindustrial atmospheric carbon budget) stored in the deep mantle and isolated from global carbon cycle. As such, the amounts of subducted slabs stagnated at mantle transition zone can be an important factor regulating the climate.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2022JB025169
