The incorporation of water into lower-mantle perovskites: A first-principles study

• Published in: Earth and planetary science letters 2013-02, Vol.364, p.37-43
• Main Authors: Hernández, E.R., Alfè, D., Brodholt, J.
• Format: Article
• Language: English
• Subjects: Coefficients; Earth; first principles simulation; Iron; Mathematical analysis; partition coefficient; Partitioning; Partitions; Periclase; Perovskites; water in mantle minerals
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2013.01.005

We have used first principles methods to calculate the partitioning of water between perovskite and ringwoodite under lower mantle and Fe-free conditions. We find that incorporation of water into ringwoodite is more favourable than into perovskite by about 0.25eV per formula unit, or about 24kJ/mol. This translates to a ringwoodite to perovskite partition coefficient of between 10 and 13, depending on temperature. These values are in good agreement with the partitioning experiments of Inoue et al. (2010) on Fe-bearing samples, where they find a partition coefficient of about 15. We also find that water incorporates into perovskite more readily than into periclase (also under Fe-free conditions), and we predict a perovskite to periclase partition coefficient of 90 at 24GPa and 1500K. We conclude, therefore, that the lower-mantle is able to contain substantial amounts of water, perhaps as much as 1000ppm. [Display omitted] ► We model the ringwoodite-to-perovskite plus periclase phase boundary from first principles. ► We determine low-energy configurations of proton–vacancy complex structures in mantle minerals. ► We model the adsorption of water in lower mantle minerals from first principles calculations.