Japan Geoscience Union Meeting 2018

Presentation information

[EE] Evening Poster

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT20] Structure and Dynamics of Earth and Planetary Mantles

Mon. May 21, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Takashi Yoshino(Institute for Planetary Materials, Okayama University), Dapeng Zhao(Department of Geophysics, Tohoku University), Takashi Nakagawa(海洋研究開発機構数理科学・先端技術研究分野)

[SIT20-P09] Coupled substitution of Fe3+ and H+ for Si in wadsleyite

*Takaaki Kawazoe1 (1.Department of Earth and Planetary Systems Science, Hiroshima Univ.)

Keywords:wadsleyite, water, hydrogen, ferric iron, Si

Wadsleyite is the most abundant mineral in the upper part of the mantle transition zone (MTZ) and can incorporate up to 3 wt% water in its crystal structure. Incorporation of water (or hydrogen) in wadsleyite influences its elasticity, atomic diffusivity, creep strength, crystallographic preferred orientation, grain-growth kinetics and electrical conductivity. Moreover, water affects phase boundaries relevant to wadsleyite. Consequently, determination of the substitution mechanisms of hydrogen in wadsleyite is fundamentally important to addressing the effects of water on the above properties of the upper MTZ. The major substitution mechanism of hydrogen in Fe-free hydrous wadsleyite is protonation of oxygen having no bonding to Si (non-silicate oxygen, O1). Recently, coupled substitution of Fe3+ and H+ for Si was proposed as a new protonation mechanism in Fe-bearing hydrous wadsleyite (Bolfan-Casanova et al. 2012; Smyth et al. 2014; Kawazoe et al. 2016). I will review the previous studies and introduce experimental evidence to support the coupled substitution of Fe3+ and H+ for Si in wadsleyite.