Effects of Oxygen Fugacity on Hydroxyl Incorporation in Garnet at 1–3 GPa and 800–1000°C and Implications for Water Storage in the Mantle

Abstract Garnet, an important mineral component in Earth's interior, usually contains minor water as structural OH, but experimental data on OH incorporation the a function of chemical and thermodynamic parameters remain rare. In particular, role oxygen fugacity ( f O 2 ) that is variable Earth has not been well assessed. We examine effects at 1–3 GPa 800–1000°C, by H‐annealing gem‐quality spessartine‐rich, grossular‐rich, pyrope‐rich garnets. For each type annealed garnet, peak positions spectral shapes are same, suggesting same mechanism(s). Under identical conditions, spessartine‐rich grossular‐rich garnets rich with solubility orders magnitudes greater than for Over studied increases pressure temperature decreases . The negative correlation probably due to Fe 3+ 2+ reduction more reduced conditions coupled structure. significant Fe‐rich ascertained small peridotite garnets, together comparisons relevant studies, suggest mantle garnet unlikely be major carrier. combination literature‐reported positive olivine, partition coefficient between olivine upper expected redox‐dependent.