Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle
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 more »
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Publication Date:
NSF-PAR ID:
10301895
Journal Name:
Minerals
Volume:
10
Issue:
4
Page Range or eLocation-ID:
330
ISSN:
2075-163X
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