Phase stability and thermal equation of state of δ-AlOOH: Implication for water transportation to the Deep Lower Mantle

Duan, Yunfei; Sun, Ningyu; Wang, Siheng; Li, Xinyang; Guo, Xuan; Ni, Huaiwei; Prakapenka, Vitali B.; Mao, Zhu

doi:10.1016/j.epsl.2018.05.003

Cited by 54 publications

(51 citation statements)

References 74 publications

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“…As the δ-(Al,Fe)OOH is subducted to the lowermost mantle where it remains stable (Duan et al, 2018;Ohira et al, 2019;, the exceptionally low thermal conductivity could play a key role in affecting the route of water transportation and local thermo-chemical structures at the base of the mantle. Again, assuming its thermal conductivity follows a typical T -1/2 dependence, at the lowermost mantle, the (Hsieh et al, 2018).…”

Section: Local Thermal Insulating Effect At the Lowermost Mantlementioning

confidence: 99%

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Hsieh

Ishii

Chao

et al. 2020

Geophysical Research Letters

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Seismic anomalies observed in Earth's deep mantle are conventionally considered to be associated with thermal and compositional anomalies, and possibly partial melt of major lower‐mantle phases. However, through deep water cycle, impacts of hydrous minerals on geophysical observables and on the deep mantle thermal state and geodynamics remain poorly understood. Here we precisely measured thermal conductivity of δ‐(Al,Fe)OOH, an important water‐carrying mineral in Earth's deep interior, to lowermost mantle pressures at room temperature. The thermal conductivity varies drastically by twofold to threefold across the spin transition of iron, resulting in an exceptionally low thermal conductivity at the lowermost mantle conditions. As δ‐(Al,Fe)OOH is transported to the lowermost mantle, its exceptionally low thermal conductivity may serve as a local thermal insulator, promoting high‐temperature anomalies and the formation of partial melt and thermal plumes at the base of the mantle, strongly influencing thermo‐chemical profiles in the region and fate of Earth's deep water cycle.

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Section: Local Thermal Insulating Effect At the Lowermost Mantlementioning

confidence: 99%

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Hsieh

Ishii

Chao

et al. 2020

Geophysical Research Letters

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“…The major components of the lower mantle are made of nominally anhydrous minerals, which contain no more than 1 weight percent of water [1,2]. However, recent discoveries of deep hydrous phase (DHP) including δ-AlOOH [3][4][5], phase H [6], HH-phase [7], and pyrite-type FeO 2 Hx [8,9], which were synthesized at conditions of cold mantle geotherm from natural minerals like diaspore (α-AlOOH) and goethite (α-FeOOH), provide possible mechanisms to transport a significant amount of water to the bottom of the mantle. The potential presence of hydrogen is likely to contribute a variety of seismological features observed at Earth's lower mantle.…”

Section: Introductionmentioning

confidence: 99%

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

et al. 2019

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Hydrogen in hydrous minerals becomes highly mobile as it approaches the geotherm of the lower mantle. Its diffusion and transportation behaviors under high pressure are important in order to understand the crystallographic properties of hydrous minerals. However, they are difficult to characterize due to the limit of weak X-ray signals from hydrogen. In this study, we measured the volume changes of hydrous ε-FeOOH under quasi-hydrostatic and non-hydrostatic conditions. Its equation of states was set as the cap line to compare with ε-FeOOH reheated and decompression from the higher pressure pyrite-FeO 2 Hx phase with 0 < x < 1. We found the volumes of those re-crystallized ε-FeOOH were generally 2.2% to 2.7% lower than fully hydrogenated ε-FeOOH. Our observations indicated that ε-FeOOH transformed from pyrite-FeO 2 Hx may inherit the hydrogen loss that occurred at the pyrite-phase. Hydrous minerals with partial dehydrogenation like ε-FeOOHx may bring it to a shallower depth (e.g., < 1700 km) of the lower mantle.

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“…A recent experimental study found that (Fe,Al)O 2 H (the solid solution phase of AlO 2 H and FeO 2 H) is stable at 107–136 GPa and 2,400 K (Zhang et al, ). Duan et al (), on the other hand, reported that AlOOH dehydrates at 2,500 K and 142 GPa. As AlO 2 H is likely more refractory than FeO 2 H (He et al, ), the incorporation of Al in P phase may not significantly increase its melting temperature.…”

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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Phase stability and thermal equation of state of δ-AlOOH: Implication for water transportation to the Deep Lower Mantle

Cited by 54 publications

References 74 publications

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

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

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Phase stability and thermal equation of state of δ-AlOOH: Implication for water transportation to the Deep Lower Mantle

Cited by 54 publications

References 74 publications

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Spin Transition of Iron in δ‐(Al,Fe)OOH Induces Thermal Anomalies in Earth's Lower Mantle

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

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

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