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Solubility of hydrogen and ferric iron in rutile and TiO 2 (II): Implications for phase assemblages during ultrahigh‐pressure metamorphism and for the stability of silica polymorphs in the lower mantle
Author(s) -
Bromiley Geoffrey,
Hilaret Nadège,
McCammon Catherine
Publication year - 2004
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2004gl019430
Subject(s) - stishovite , rutile , octahedron , solubility , hydrogen , materials science , phase (matter) , oxygen , crystallography , mineralogy , geology , inorganic chemistry , crystal structure , chemistry , quartz , metallurgy , paleontology , organic chemistry
The solubility of hydrogen in Fe 2 O 3 ‐doped rutile and TiO 2 (II) at 1100°C has been experimentally determined. H incorporation in rutile is coupled to substitution of Fe 3+ onto the octahedral Ti 4+ site. In contrast, TiO 2 (II) contains no structurally‐incorporated hydrogen. The dominant Fe 3+ incorporation mechanism in both phases is unrelated to H content, and involves substitution of Fe 3+ onto octahedral Ti 4+ sites, charge‐balanced by oxygen vacancies. Substitution of Fe 2 O 3 into TiO 2 (II) stabilizes the structure to much lower pressures than in the pure TiO 2 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 α‐PbO 2 structure would represent a significant dehydration event at the base of the lower mantle.