[S-IT07] Structure and dynamics of Earth and Planetary deep interiors

[SIT07-11] H-D inter-diffusion in Fe-free wadsleyite: implication for multiple hydrogen mechanism

*Wei Sun¹, Takashi Yoshino¹, Naoya Sakamoto², Hisayoshi Yurimoto³ (1.Research Group of Physics of the Earth's Interior at the Institute for Study of the Earth's Interior, Okayama University, 2.Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, 3.Department of Natural History Sciences, Hokkaido University)

Keywords:inter-diffusion, wadsleyite, asymmetric, multiple

It has been proposed that concentration and speciation of water-derived species in minerals may adjust in response to changes of points defect condition [Demouchy and Mackwell, 2006], To lift the veil of Fe effect on hydrogen diffusion and isotopic differentiation, a sets of H-D inter-diffusion experiments were conducted in Fe-free wadsleyite single crystal couples at various temperatures, 16 GPa and compared with our former study on Fe-bearing wadsleyite. Distinguish with symmetric profiles in Fe-bearing condition, H-D inter-diffusion in Fe-free wadsleyite revealed evidently asymmetric properties and it indicates deuterium diffuses about 1 order faster than hydrogen in Fe-free wadsleyite. Both magnitude and anisotropy of H-D inter-diffusion in Fe-free condition are largely different with Fe-bearing condition, which strongly demonstrated a multiple hydrogen mechanism proposed by Karato (2013) association with free proton migration in interstitial sites. Simulation model suggests free proton migration in interstitial sites dominates the hydrogen diffusion in Fe-free condition and asymmetric properties might owe to the distinguished jumping probabilities from Mg sites to interstitial sites between hydrogen and deuterium.