Determination of hydrogen sites of nominally anhydrous minerals of the mantle transition zone

Sano, Asami   ; Kuribayashi, Takahiro*; Komatsu, Kazuki*; Yagi, Takehiko*; Otani, Eiji*

Wadsleyite is a main constituent of upper part of the mantle transition zone, at 410 - 520 km depth of the earth. Since the Smyth's prediction, wadsleyite, which is one of the nominally anhydrous mineral (NAMs) have been attracted as a host of water in the mantle. Subsequent studies have also revealed that a small amount of hydrogen cause changes of some physical properties of wadsleyite dramatically. To understand the effect of hydration of wadsleyite on its physical properties, it is essential to know the position of hydrogen in the structure. In this study, we intend to determine the hydrogen position of wadsleyite by neutron powder diffraction experiment. Full Rietveld refinement with deuterium was successfully conducted, which revealed that an O-D bond is formed at the edge of the M3 octahedron between the O1...O4 (3.074 A).