title: Dehydrogenation of goethite in Earth's deep lower mantle.
abstract: 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 FeO2H 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 FeO2HxUsing a combination of theoretical simulations and high-pressure-temperature experiments, we calibrated thexdependence 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 lowerx, 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.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China.|Department of Geological Sciences, Stanford University, Stanford, CA 94305.|Geophysical Laboratory, Carnegie Institution, Washington, DC 20015.
authors.forename: Qingyang
authors.initials: Q
authors.lastname: Hu
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China.
authors.forename: Duck Young
authors.initials: DY
authors.lastname: Kim
authors.affiliation: Department of Geological Sciences, Stanford University, Stanford, CA 94305.
authors.forename: Jin
authors.initials: J
authors.lastname: Liu
authors.affiliation: High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution, Argonne, IL 60439.
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China.|Geophysical Laboratory, Carnegie Institution, Washington, DC 20015.
authors.forename: Liuxiang
authors.initials: L
authors.lastname: Yang
authors.affiliation: Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, HI 96822.
authors.forename: Dongzhou
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Geological Sciences, Stanford University, Stanford, CA 94305.
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China; hmao@ciw.edu.|Geophysical Laboratory, Carnegie Institution, Washington, DC 20015.
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
keywords: FeO2; FeO2H; P phase; dehydrogenation; high pressure