Chemical Reactions Between Fe and H<sub>2</sub>O up to Megabar Pressures and Implications for Water Storage in the Earth's Mantle and Core

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

doi:10.1002/2017gl075720

Cited by 46 publications

(49 citation statements)

References 59 publications

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“…It is also suggested that pyrite‐type FeOOH may result from the reaction between Fe and H 2 O at the core‐mantle boundary because this structure is stable at pressures above 80 GPa in FeOOH (e.g., Liu et al, ; Mao et al, ; Nishi et al, ; Ohtani et al, ; Yuan et al, ). AlOOH and FeOOH likely form a solid solution in the pyrite‐type structure because recent theoretical studies indicated that pyrite‐type AlOOH stabilizes at high pressures (Tsuchiya & Tsuchiya, ; Verma et al, ).…”

Section: Discussionmentioning

confidence: 99%

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

et al. 2019

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The high-pressure solid solution and compression behavior of hydroxides in the ternary MgSiO 4 H 2 -AlOOH-FeOOH system were studied at pressures of 16-60 GPa and temperatures of 300-1513 K. We applied in situ X-ray measurements in conjunction with a multianvil apparatus using sintered diamond anvils to achieve homogeneous temperature distributions within large sample volumes. Our results show that CaCl 2 -type hydroxides form solid solutions over a wide composition range. We also observed the volume reductions in the solid solutions accompanied by a spin transition of iron at~50 GPa, and the wide compositional ranges are maintained through this process. Consequently, water may be transported into the deep lower mantle by the hydrous CaCl 2 -type solid solution with changing its composition depending on the chemical and thermal environments.Plain Language Summary A significant amount of water has been transported into the Earth's interior via subduction of hydrous phases in cold plates since plate tectonics started to operate billions of years ago. Recent theoretical and experimental studies revealed that hydrous phases with compositions of MgSiO 4 H 2 , AlOOH, and FeOOH are stable at the high pressures occurring in the lower mantle, suggesting that a certain amount of water may be delivered to the core-mantle boundary (~2,900-km depth). However, hydroxides in multicomponent systems relevant to the actual mantle and subducting slabs are not well studied. Here we compressed multicomponent hydroxides in the ternary MgSiO 4 H 2 -AlOOH-FeOOH system using multianvil technology and found that hydroxide subducted into the lower mantle can retain Earth's major elements, such as Mg, Si, Al, Fe, and O. Key Points:• The solid solution and compression behavior of hydroxides were studied by in situ X-ray measurements and a multianvil press • CaCl 2 -type hydroxides form solid solutions over a wide composition range in the MgSiO 4 H 2 -AlOOH-FeOOH system • The volume of CaCl 2 -type hydroxides decreases due to a spin transition of iron at~50 GPa Supporting Information:• Supporting Information S1Correspondence to: M. Nishi,

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Section: Discussionmentioning

confidence: 99%

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

et al. 2019

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“…Moreover, other contexts than subduction generate a broad geophysical interest for studying the Fe-O-H system at high pressure. Reaction of these deep hydrous melt with the metallic iron-rich lower mantle material (Frost et al, 2004) may produce FeO 2 H x in the lower mantle (Yuan et al, 2018). Iron hydride FeH x indeed satisfies density and sound velocities constraints in the Earth's core (e.g., Tagawa et al, 2016).…”

Section: Discussionmentioning

confidence: 87%

“…However, crystalline-bounded water almost certainly survive shallow subduction and is recycled to large depth, particularly in cold slabs (Van Keken et al, 2011). Pyrite-structured FeO 2 H x was indeed reported to result from the reaction of water with metallic iron Mao et al, 2017;Yuan et al, 2018), a reaction that may have taken place during core formation resulting in the delivery of hydrogen to the Earth's core (Yuan et al, 2018). Moreover, other contexts than subduction generate a broad geophysical interest for studying the Fe-O-H system at high pressure.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, dehydration melting of transition zone materials swept down to the lower mantle by mantle convection or melting of dense hydrous magnesium phases in subducting slabs that are stagnating near 660-km seismic discontinuity could produce deep hydrous melts at the top of the lower mantle. Reaction of these deep hydrous melt with the metallic iron-rich lower mantle material (Frost et al, 2004) may produce FeO 2 H x in the lower mantle (Yuan et al, 2018). The dense FeO 2 H x peroxide-bearing phase would sink to the core-mantle boundary where it would accumulate.…”

Section: 1029/2019gl081922mentioning

confidence: 99%

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Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

Boulard

Harmand

Guyot

et al. 2019

Geophysical Research Letters

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Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite‐type FeO2 and FeO2Hx phases stable at deep terrestrial lower mantle pressures and temperatures. In the present study, we probed the iron oxidation state in high‐pressure transformation products of Fe3+OOH goethite by in situ X‐ray absorption spectroscopy in laser‐heated diamond‐anvil cell. At pressures and temperatures of ~91 GPa and 1,500–2,350 K, respectively, that is, in the previously reported stability field of FeO2Hx, a measured shift of −3.3 ± 0.1 eV of the Fe K‐edge demonstrates that iron has turned from Fe3+ to Fe2+. We interpret this reductive valence change of iron by a concomitant oxidation of oxygen atoms from O2− to O−, in agreement with previous suggestions based on the structures of pyrite‐type FeO2 and FeO2Hx phases. Such peculiar chemistry could drastically change our view of crystal chemistry in deep planetary interiors.

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“…Comparison between the melting temperatures of FeO 2 and FeO 2 H with mantle geotherms together with high‐pressure experiments (e.g., Liu et al, ; Yuan et al, ) suggests that P phase is thermally stable (not melted) in most of the mantle (Anderson, , ; Brown & Shankland, ). However, this may not be the case in the lowermost mantle and within the thermal boundary layer right above the CMB where mantle temperatures drastically increase by 1,000–1,400 K within less than 200 km estimated from mantle adiabat and the melting temperature of core materials at CMB conditions (Anderson, ; Anzellini et al, ; Morard et al, ).…”

Section: Resultsmentioning

confidence: 99%

First‐Principles Study of FeO₂H_x Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones

et al. 2019

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Pyrite-type FeO 2 H x (P phase) has recently been suggested as a possible alternative to explain ultralow-velocity zones due to its low seismic velocity and high density. Here we report the results on the congruent melting temperature and melt properties of P phase at high pressures from first-principles molecular dynamics simulations. The results show that P phase would likely be melted near the core-mantle boundary. Liquid FeO 2 H x has smaller density and smaller bulk sound velocity compared to the isochemical P phase. As such, relatively small amounts of liquid FeO 2 H x could account for the observed seismic anomaly of ultralow-velocity zones. However, to maintain the liquid FeO 2 H x within the ultralow-velocity zones against compaction requires special physical conditions, such as relatively high viscosity of the solid matrix and/or vigorous convection of the overlying mantle.Plain Language Summary Ultralow-velocity zones (ULVZs) are 5-40-km-thick patches lying above Earth's core-mantle boundary. They are characterized with anomalously low seismic velocities compared with the ambient mantle and may contain important clues on the thermochemical evolution of the Earth. A recent experimental study argued that ULVZs may be caused by the accumulation of pyrite-type FeO 2 H x (P phase) at the bottom of the mantle. Here for the first time, we systematically study the thermoelastic properties of both FeO 2 H x solid and liquid phases. We find that P phase is likely melted near the core-mantle boundary and thus cannot be the source of ULVZs. Furthermore, in order for the molten product of P phase to cause ULVZs, the dense and nearly inviscid melts must be dynamically stable and confined within the ULVZs, which requires that the mantle is highly viscous and/or convects vigorously.

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

Cited by 46 publications

References 59 publications

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

First‐Principles Study of FeO₂H_x Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones

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

Cited by 46 publications

References 59 publications

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

Solid Solution and Compression Behavior of Hydroxides in the Lower Mantle

Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

First‐Principles Study of FeO2Hx Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones

Contact Info

Product

Resources

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

First‐Principles Study of FeO₂H_x Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones