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Title: Dehydrogenation of goethite in Earth’s deep lower mantle

The cycling of hydrogen influences the structure, composition, and stratification of Earth’s interior. Our recent discovery of pyrite-structured iron peroxide (designated as the P phase) and the formation of the P phase from dehydrogenation of goethite FeO 2H implies the separation of the oxygen and hydrogen cycles in the deep lower mantle beneath 1,800 km. Here we further characterize the residual hydrogen, x, in the P-phase FeO 2Hx. Using a combination of theoretical simulations and high-pressure–temperature experiments, we calibrated the x dependence of molar volume of the P phase. Within the current range of experimental conditions, we observed a compositional range of P phase of 0.39 < x < 0.81, corresponding to 19–61% dehydrogenation. Increasing temperature and heating time will help release hydrogen and lower x, suggesting that dehydrogenation could be approaching completion at the high-temperature conditions of the lower mantle over extended geological time. Our observations indicate a fundamental change in the mode of hydrogen release from dehydration in the upper mantle to dehydrogenation in the deep lower mantle, thus differentiating the deep hydrogen and hydrous cycles.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [3] ;  [5]
  1. Center for High Pressure Science and Technology Advanced Research, Shanghai (China); Stanford Univ., CA (United States). Dept. of Geological Sciences; Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab.
  2. Center for High Pressure Science and Technology Advanced Research, Shanghai (China)
  3. Stanford Univ., CA (United States). Dept. of Geological Sciences
  4. Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab., High Pressure Collaborative Access Team (HPCAT)
  5. Center for High Pressure Science and Technology Advanced Research, Shanghai (China); Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab.
  6. Univ. of Hawaii at Manoa, Honolulu, HI (United States). Hawaii Inst. of Geophysics and Planetology, School of Ocean and Earth Science and Technology
Publication Date:
Grant/Contract Number:
NA0001974; FG02-99ER45775
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 7; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES
OSTI Identifier:
1341909
Alternate Identifier(s):
OSTI ID: 1344573