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Water has no significant effect on oxygen self-diffuison rate in forsterite

Hongzhan Fei1,2, Michael Wiedenbeck3, Daisuke Yamazaki2, Tomoo Katsura1

1Bayerisches Geoinstitut, University of Bayreuth, D95440, Bayreuth, Germany
2Institute for Study of the Earth’s Interior, Okayama University, 682-0193, Misasa, Tottori, Japan
3Helmholtz Centre Potsdam, D14473, Potsdam, Germany

Citation: Fei, H., et al. (2014), J. Geophys. Res. 119. Doi: 10.1002/2014JB011141.  full text

Water is thought to play an essential role in dyanmical processes in the Earth's interior. A number of studies haver reported a significant influence for water on the physical properties of mantle mineralss, e.g., electrical properties, elastic moduli, creep rates, atomic diffusivity, deformation fabric, and so on.

In the case of rheology, it was believed that even several tens wt. ppm of water could enhance creep rate in olivine by orders of magnitude. However, this conception is recently withdrawed by Fei et al. (Nature 2013) based on silicon self-diffusion experiments because the creep rate of olivine is believed to be controlled by self-diffuison of silicon, which is the slowest diffusion species in olivine. On the other hand, oxygen is the second slowest diffuison species with similar diffusion rate as silicon, and it may also play an essential role in the creep of olivine. In this study, we systematically meaured oxygen self-diffusion coefficient in iron-free olivine, namely, forsterite, at 8 GPa, 1600-1800 K, with water content range from <1 up to ~800 wt. ppm. The result clearly shows that water has no siginiciantly effect on oxygen self-diffusion rate in forsterite (Fig. 1). Together with the small effect of water on silicon self-diffuison, we conclude that the role of water on olivine creep is not essential.

Fig. 1. Oxygen self-diffusion coefficient in forsterite against water content