Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth's lowermost mantle

Yuan, Hongsheng; Zhang, Li; Ohtani, Eiji; Meng, Yue; Greenberg, Eran; Prakapenka, Vitali B.

doi:10.1016/j.epsl.2019.115714

Cited by 26 publications

(45 citation statements)

References 47 publications

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“…We also note that the pressure conditions where we observed -FeOOH (between 100 and 110 GPa) are higher than previous reports for pure Fe end-member (below 80 GPa) [31]. We therefore hypothesize that the occurrence of -FeOOH above 100 GPa in our experiments might be caused by the presence of Al, which could stabilize the structure at higher pressures than its Al-free counterpart [32]. Although our measured unit-cell volumes of the phase is close to that of reported Al-free -FeOOH (Figure 4), we cannot rule out the possibility of a small amount of Al in the phase.…”

Section: Reaction Between Iron Metal and H 2 O Released From δ-Alooh contrasting

confidence: 60%

“…Previous high-pressure experiments have shown that when Al-bearing bridgmanite reacts with H 2 O, it can reduce the amount of Al in bridgmanite and form a separate AlOOH-MgSiO 2 (OH) 2 phase [8], also called phase H. These experiments also found that the presence of Al in the structure of phase H increases its thermal stability. Similarly, -FeOOH can form at least a partial solid solution with δ-AlOOH [32]. Last but not least, Chen et al [11] found that Al is separated from CaSiO 3 perovskite in the presence of H 2 O and forms a separate δ-AlOOH phase at high pressures.…”

Section: Discussionmentioning

confidence: 99%

“…We did not see evidence of reaction between H 2 O and metallic iron up to 45 GPa. However, if H 2 O released from the dehydration of δ-AlOOH above 2100 km was to react with metallic iron, the process could oxidize metallic iron to form FeOOH as a separate phase or as a component in phase H [32]. If such a reaction indeed occurs, it would reduce the redox buffering capability in the dehydration zone at the mid mantle.…”

Section: Discussionmentioning

confidence: 99%

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Dehydration of δ-AlOOH in Earth’s Deep Lower Mantle

et al. 2020

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δ -AlOOH has been shown to be stable at the pressure–temperature conditions of the lower mantle. However, its stability remains uncertain at the conditions expected for the lowermost mantle where temperature is expected to rise quickly with increasing depth. Our laser-heated diamond-anvil cell experiments show that δ -AlOOH undergoes dehydration at ∼2000 K above 90 GPa. This dehydration temperature is lower than geotherm temperatures expected at the bottom ∼700 km of the mantle and suggests that δ -AlOOH in warm slabs would dehydrate in this region. Our experiments also show that the released H 2 O from dehydration of δ -AlOOH can react with metallic iron, forming iron oxide, iron hydroxide, and possibly iron hydride. Our observations suggest that H 2 O from the dehydration of subducting slabs, if it occurs, could alter the chemical composition of the surrounding mantle and core regions.

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Section: Reaction Between Iron Metal and H 2 O Released From δ-Alooh contrasting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Dehydration of δ-AlOOH in Earth’s Deep Lower Mantle

et al. 2020

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“…AlOOH was found to coexist with bridgmanite at 104126 GPa and 17502500 K, indicating that it is a promising candidate hydrous phase in the deep mantle (Yuan et al, 2019). Therefore, it may deliver water down to the bottom of the mantle and extend the deep water cycle throughout the whole mantle (Duan et al, 2018;Kawazoe et al, 2017;Sano et al, 2008;Yuan et al, 2019). If iron-bearing δ-AlOOH accumulates at the lowermost mantle via cold subducting oceanic slabs, it likely dehydrates near the core-mantle boundary due to the steep increase in temperature with depth (Yuan et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…The incorporation of FeOOH could induce profound impacts on the physical properties of δ-AlOOH in the deep mantle (e.g., spin transition, elasticity, and thermal conductivity) (Hsieh et al, 2020;Kawazoe et al, 2017;Ohira et al, 2019;Su et al, 2020). It would further affect the global geochemical cycling of ferric iron and water (hydrogen) in the deep mantle (Yuan et al, 2019;Zhang et al, 2018). It is found that iron-bearing δ-AlOOH phase, δ-(Al 0.824 Fe 0.126 )OOH 1.15 and δ-(Al 0.908 Fe 0.045 )OOH 1.14 , exhibits elastic anomalies across the spin transition, including isothermal bulk modulus K T , bulk sound velocity V Φ , and the ratio of density over bulk sound velocity ρ/V Φ (Ohira et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic evidence for the Fe3+ spin transition in iron-bearing δ-AlOOH at high pressure

Zhao

et al. 2021

American Mineralogist

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δ-AlOOH has emerged as a promising candidate for water storage in the lower mantle and could have delivered water into the bottom of the mantle. To date, it still remains unclear how the presence of iron affects its elastic, rheological, vibrational, and transport properties, especially across the spin crossover. Here, we conducted high-pressure X-ray emission spectroscopy experiments on a δ-(Al0.85Fe0.15) OOH sample up to 53 GPa using silicone oil as the pressure transmitting medium in a diamond-anvil cell. We also carried out laser Raman measurements on δ-(Al0.85Fe0.15)OOH and δ-(Al0.52Fe0.48)OOH up to 57 and 62 GPa, respectively, using neon as the pressure-transmitting medium. Evolution of Raman spectra of δ-(Al0.85Fe0.15)OOH with pressure shows two new bands at 226 and 632 cm−1 at 6.0 GPa, in agreement with the transition from an ordered (P21nm) to a disordered hydrogen bonding structure (Pnnm) for δ-AlOOH. Similarly, the two new Raman bands at 155 and 539 cm−1 appear in δ-(Al0.52Fe0.48)OOH between 8.5 and 15.8 GPa, indicating that the incorporation of 48 mol% FeOOH could postpone the order-disorder transition upon compression. On the other hand, the satellite peak (Kβ′) intensity of δ-(Al0.85Fe0.15)OOH starts to decrease at ~30 GPa and it disappears completely at 42 GPa. That is, δ-(Al0.85Fe0.15)OOH undergoes a gradual electronic spin-pairing transition at 30–42 GPa. Furthermore, the pressure dependence of Raman shifts of δ-(Al0.85Fe0.15)OOH discontinuously decreases at 32–37 GPa, suggesting that the improved hydrostaticity by the use of neon pressure medium could lead to a relatively narrow spin crossover. Notably, the pressure dependence of Raman shifts and optical color of δ-(Al0.52Fe0.48)OOH dramatically change at 41–45 GPa, suggesting that it probably undergoes a relatively sharp spin transition in the neon pressure medium. Together with literature data on the solid solutions between δ-AlOOH and ε-FeOOH, we found that the onset pressure of the spin transition in δ-(Al,Fe)OOH increases with increasing FeOOH content. These results shed new insights into the effects of iron on the structural evolution and vibrational properties of δ-AlOOH. The presence of FeOOH in δ-AlOOH can substantially influence its high-pressure behavior and stability at the deep mantle conditions and play an important role in the deep-water cycle.

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