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Title: Evidence for oxygenation of Fe-Mg oxides at mid-mantle conditions and the rise of deep oxygen

Journal Article · · National Science Review
DOI:https://doi.org/10.1093/nsr/nwaa096· OSTI ID:1780165
ORCiD logo [1];  [2];  [3];  [4];  [5];  [3];  [6]; ORCiD logo [3];  [3];  [7]
  1. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing 100094, China, Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA
  2. Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA
  3. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing 100094, China
  4. School of Earth and Space Sciences, Peking University, Beijing 100871, China
  5. SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
  6. Center for Study of Matter at Extreme Conditions, Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33199, USA
  7. Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
+ Show Author Affiliations

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 40 gigapascal when (Mg, Fe)-bearing hydrous materials are heated over 1500 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 1000 km in the Earth's mantle. The emergence of oxygen-excess reservoirs out of primordial or subducted (Mg, Fe)-bearing hydrous materials may revise our view on the deep-mantle redox chemistry.

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES); National Natural Science Foundation of China (NSFC); National Science Foundation (NSF); SPring-8 Japan
Grant/Contract Number:
FG02–94ER14466; 2019A1284; 2019B1203; AC02– 06CH11357; U1930401; 17N1051–0213; EAR 1446969; EAR-1723185; EAR-1722515; EAR-1447438; EAR1634415; ECCS-1542152
OSTI ID:
1780165
Alternate ID(s):
OSTI ID: 1656686; OSTI ID: 1786003
Journal Information:
National Science Review, Journal Name: National Science Review Vol. 8 Journal Issue: 4; ISSN 2095-5138
Publisher:
Oxford University PressCopyright Statement
Country of Publication:
China
Language:
English

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Related Subjects

58 GEOSCIENCES
subducting slab
hydrous phase
lower mantle
deep oxygen
oxygen-excess oxides