Chemical Reactions Between Fe and H2O up to Megabar Pressures and Implications for Water Storage in the Earth's Mantle and Core

Liang Yuan, Eiji Otani, Daijo Ikuta, Seiji Kamada, Jun Tsuchiya, Hirao Naohisa, Yasuo Ohishi, Akio Suzuki

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

We investigated the phase relations of the Fe-H2O system at high pressures based on in situ X-ray diffraction experiments and first-principles calculations and demonstrate that FeHx and FeO are present at pressures less than ~78 GPa. A recently reported pyrite-structured FeO2 was identified in the Fe-H2O system at pressures greater than ~78 GPa after laser heating. The phase observed in this study has a unit cell volume 8%–11% larger than that of FeO2, produced in the Fe-O binary system reported previously, suggesting that hydrogen might be retained in a FeO2Hx crystal structure. Our observations indicate that H2O is likely introduced into the deep Earth through reaction between iron and water during the accretion and separation of the metallic core. Additionally, reaction between Fe and H2O would occur at the core-mantle boundary, given water released from hydrous subducting slabs that intersect with the metallic core. Accumulation of volatile-bearing iron compounds may provide new insights into the enigmatic seismic structures observed at the base of the lower mantle.

Original languageEnglish
Pages (from-to)1330-1338
Number of pages9
JournalGeophysical Research Letters
Volume45
Issue number3
DOIs
Publication statusPublished - 2018 Feb 16

Keywords

  • Iron
  • high pressures
  • high temperatures
  • pyrite-structured FeOOH
  • water

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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