Solubility of hydrogen and ferric iron in rutile and TiO2 (II):: Implications for phase assemblages during ultrahigh-pressure metamorphism and for the stability of silica polymorphs in the lower mantle -: art. no. L04610

The solubility of hydrogen in Fe2O3-doped rutile and TiO2 (II) at 1100 degreesC has been experimentally determined. H incorporation in rutile is coupled to substitution of Fe3+ onto the octahedral Ti4+ site. In contrast, TiO2 (II) contains no structurally-incorporated hydrogen. The dominant Fe3+ incorporation mechanism in both phases is unrelated to H content, and involves substitution of Fe3+ onto octahedral Ti4+ sites, charge-balanced by oxygen vacancies. Substitution of Fe2O3 into TiO2 (II) stabilizes the structure to much lower pressures than in the pure TiO2 system. Results indicate that Al-bearing stishovite could act as an important carrier of water in subducting oceanic crust, but that formation of the post-stishovite phase with the alpha-PbO2 structure would represent a significant dehydration event at the base of the lower mantle.