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Open AccessArticle

Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle

1
School of Earth Sciences, Ohio State University, Columbus, OH 43210, USA
2
CNRS, Laboratoire de Geologie de Lyon, Ecole Normale Supérieure de Lyon, 69364 Lyon, France
3
The Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Postbox 1028 Blindern, N-0315 Oslo, Norway
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(4), 330; https://doi.org/10.3390/min10040330
Received: 14 February 2020 / Revised: 26 March 2020 / Accepted: 28 March 2020 / Published: 8 April 2020
(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)
The degree to which the Earth’s mantle stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under mantle-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H, are stable to the pressures and temperatures of the Earth’s lower mantle, suggesting that the Earth’s lower mantle may participate in the cycling of water. We build on our prior work of density functional theory calculations on phase H with the stability, structure, and bonding of hydrous phases D, and we predict the aluminum partitioning with H in the Al 2 O 3 -SiO 2 -MgO-H 2 O system. We address the solid solutions through a statistical sampling of site occupancy and calculation of the partition function from the grand canonical ensemble. We show that each phase has a wide solid solution series between MgSi 2 O 6 H 2 -Al 2 SiO 6 H 2 and MgSiO 4 H 2 -2 δ AlOOH + SiO 2 , in which phase H is more aluminum rich than phase D at a given bulk composition. We predict that the addition of Al to both phases D and H stabilizes each phase to higher temperatures through additional configurational entropy. While we have shown that phase H does not exhibit symmetric hydrogen bonding at high pressure, we report here that phase D undergoes a gradual increase in the number of symmetric H-bonds beginning at ∼30 GPa, and it is only ∼50% complete at 60 GPa. View Full-Text
Keywords: hydrous mantle minerals; density functional theory; mineral disordering hydrous mantle minerals; density functional theory; mineral disordering
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MDPI and ACS Style

Panero, W.R.; Caracas, R. Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle. Minerals 2020, 10, 330. https://doi.org/10.3390/min10040330

AMA Style

Panero WR, Caracas R. Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle. Minerals. 2020; 10(4):330. https://doi.org/10.3390/min10040330

Chicago/Turabian Style

Panero, Wendy R.; Caracas, Razvan. 2020. "Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle" Minerals 10, no. 4: 330. https://doi.org/10.3390/min10040330

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