Independent hydrogen incorporation in wadsleyite from oxygen fugacity and non-dissociation of H2O in the reducing mantle transition zone.

• The H 2 O solubility in wadsleyite is independent from oxygen fugacity. • The dissociation of H 2 O to H 2 and O 2 in the mantle transition zone is negligible. • The H 2 O-rich and low- f O2 conditions in the mantle transition zone are compatible. The mantle transition zone is considered as a potential water reservoir in the Earth's interior because of the high H 2 O solubility in wadsleyite and ringwoodite. However, this scenario is based on experiments performed under relatively oxidized conditions. In order to constrain the H 2 O solubility in minerals in the reducing (close to iron-wüstite buffer) mantle transition zone, here we systematically measured the water content in wadsleyite at 17 GPa and 1673 K, as a function of oxygen fugacity in the range of Hf-HfO 2 , Mo-MoO 2 , Re-ReO 2 , and Pt-PtO 2 buffer conditions. The results suggest that the oxygen fugacity has no meaningful effect on H 2 O solubility in wadsleyite. Wadsleyite in the mantle transition zone can store as much as ∼1.0 wt.% H 2 O in spite of the reducing conditions. The dissociation of H 2 O into H 2 and O 2 is negligible, namely, there should be negligible molecular H 2 in the mantle transition zone. [ABSTRACT FROM AUTHOR]