High‐Pressure Elasticity of δ‐(Al,Fe)OOH Single Crystals and Seismic Detectability of Hydrous MORB in the Shallow Lower Mantle

Satta, Niccolò; Criniti, Giacomo; Kurnosov, Alexander; Ballaran, Tiziana Boffa; Ishii, Takayuki; Marquardt, Hauke

doi:10.1029/2021gl094185

Cited by 10 publications

(3 citation statements)

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“…In particular, if (Al, Fe)-phase H forms due to dehydration processes at the base of the lower mantle (Ohtani, 2020), the cation concentration (and consequently, the sound velocities) may be significantly different from those measured on samples synthesized at pressures and temperatures of the mantle transition zone. Modeling of mid-ocean ridge basalt (MORB) hydration by formation of phases in the (δ-AlOOH)-(MgSiO 2 (OH) 2 )-(ε-FeOOH) solid solution may result in increased seismic velocities of hydrous MORB relative to pyrolytic mantle just below the mantle transition zone (∼680-900 km; Satta et al, 2021). However, the ν p and ν s values constrained for δ-(Al 0.97 Fe 0.03 )OOH and used in the modeling for seismic velocities of this solid solution are significantly faster than those constrained for compositions with greater concentrations of Fe: (δ-(Al 0.87 Fe 0.13 )OOH; Ohira et al (2021), (Al 0.956 Fe 0.044 )OOH; Su et al, 2021a;Su et al, 2021b).…”

Section: Discussionmentioning

confidence: 99%

Equation of State and Spin Crossover of (Al, Fe)‐Phase H

et al. 2023

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Section: Discussionmentioning

confidence: 99%

Equation of State and Spin Crossover of (Al, Fe)‐Phase H

et al. 2023

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“…DOI: https://doi.org/10.2138/am-2022-8839. http://www.minsocam.org/ studies have found stable solid solution of phase H encompassing essentially the entire ternary (Mg,Fe,Al)(Si,Fe,Al)(OOH) 2 (Nishi et al 2019), complementing studies of binary joins in this compositional space (Ohira et al 2019(Ohira et al , 2021Satta et al 2021).…”

Section: Introductionmentioning

confidence: 95%

Hydrogen bond symmetrization and high-spin to low-spin transition of ε-FeOOH at the pressure of Earth’s lower mantle

Insixiengmay,

Stixrude

2023

American Mineralogist

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We focus on the ferric end-member of phase H: 𝜀-FeOOH using density functional theory at the PBEsol+U level. At 300 K, we find that 𝜀-FeOOH undergoes a hydrogen bond symmetrization at 37 GPa and a sharp high-spin to low-spin transition at 45 GPa. We find excellent agreement with experimental measurements of equation of state, lattice parameters, atomic positions, vibrational frequencies, and optical properties as related to the band gap, which we find to be finite and small, decreasing with pressure. The hydrogen bond symmetrization transition is neither first-, nor second-order, with no discontinuity in volume or any of the elastic moduli. Computed IR and Raman frequencies and intensities show that vibrational spectroscopy may provide the best opportunity for locating the hydrogen bond symmetrization transition experimentally. We find that 𝜀-FeOOH is highly anisotropic in both longitudinal-and shear-wave velocities at all pressures, with the shear wave velocity varying with propagation and polarization direction by as much as 24% at zero pressure and 43% at 46 GPa. The shear and bulk elastic moduli increase by 18% across the high-spin to low-spin transition.Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorldWater is an important component in the mantle, which even in small concentrations can have a large effect on properties such as the melting temperature and viscosity, and thus on thermal evolution. The amount of water stored in the largest part of the mantle, the lower mantle, is still uncertain. This is partly due to the relative inaccessibility of this region, for example few physical samples from the lower mantle are known, in contrast to the increasing number of diamond inclusions and other samples from the transition zone (Pearson et al. 2014;Tschauner et al. 2018). Our uncertainty about the water content in the lower mantle is also due to a comparative lack of understanding of hydrogen bonding at high pressure: in what phases is water crystallographically stored, and what is the effect of water on physical properties at high pressure?Water storage may be fundamentally different in the lower mantle than in the transition zone. In the transition zone, copious amounts of water may be stored in nominally anhydrous minerals, including wadsleyite and ringwoodite, which have water storage capacities exceeding 1 wt. % (Hirschmann 2006). In the lower mantle, however, the water storage capacity of the major phases (bridgmanite, ferropericalse, davemaoite), while still uncertain, appears not to exceed 1200 ppm (Litasov and Ohtani 2007;Fu et al. 2019;Chen et al. 2020;Liu et al. 2021). If the lower mantle has a water concentration much higher than this, the water must be stored in hydrous phases, i.e. phases in which water is a stoichiometric component.Phase H is the hydrous phase that is found to be stable in mantle-like whole rock compositions with excess H 2 O (Walter et al. 2015) over most of the lower mantle pressure regime (55-125 GPa). These experiments were l...

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“…For instance, relatively large single crystals (>~100 μm) of high quality are required to determine physical properties such as the full elastic tensor, sound wave velocities anisotropy and thermal conductivity (e.g. Hsieh et al, 2020Hsieh et al, , 2022Satta et al 2021). To date, the structural and physical properties of Cf-type phase have been poorly constrained as measurements were conducted in limited systems and using polycrystalline samples.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and structural analysis of CaFe2O4-type single crystals in the NaAlSiO4-MgAl2O4-Fe3O4 system

Ishii

Criniti

Wang

et al. 2023

American Mineralogist

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Orthorhombic CaFe2O4-structured (Cf) Na-rich aluminous silicate (space group Pbnm) is a major mineral of metabasaltic rocks at lower mantle conditions and can therefore significantly affect the physical properties of subducted oceanic crusts. We attempted to synthesize single crystals of Cf-type phases in the systems NaAlSiO4, NaAlSiO4-MgAl2O4, NaAlSiO4-MgAl2O4-Fe3O4, and NaAlSiO4-MgAl2O4-Fe3O4-H2O at 23-26 GPa and 1100-2200 °C. Under dry conditions, single-crystals of Cf-type phase up to 100-150 μm in size were recovered from 23 GPa and 2000-2200 °C. Single-crystal X-ray diffraction and composition analyses suggest that the synthesized Cf-type phases have few percent of vacancies in the 8fold coordinated site with Na, Mg, and Fe 2+ and partially disordered Al and Si in the octahedral sites. Iron-bearing Cf-type phases have 32-34% Fe 3+ that is hosted both in the octahedral sites and in the 8-fold coordinated site. In NaAlSiO4-MgAl2O4-Fe3O4-H2O system, no formation of Cf-type phase was observed at 24 GPa and 1100-2000 °C, due to formation of hydrous Na-rich melt and Al-rich oxides or hydroxides, suggesting possible absence of Cf-type phase in hydrous basaltic crust. The single crystal syntheses of Cf-type phases will be useful to investigate their physical properties, improving models of lower mantle structure and dynamics.

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High‐Pressure Elasticity of δ‐(Al,Fe)OOH Single Crystals and Seismic Detectability of Hydrous MORB in the Shallow Lower Mantle

Cited by 10 publications

References 88 publications

Equation of State and Spin Crossover of (Al, Fe)‐Phase H

Equation of State and Spin Crossover of (Al, Fe)‐Phase H

Hydrogen bond symmetrization and high-spin to low-spin transition of ε-FeOOH at the pressure of Earth’s lower mantle

Synthesis and structural analysis of CaFe2O4-type single crystals in the NaAlSiO4-MgAl2O4-Fe3O4 system

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