Si and O self-diffusion in hydrous forsterite and iron-bearing olivine from the perspective of defect chemistry

We discuss the experimental results of silicon and oxygen self-diffusion coefficients in forsterite and iron-bearing olivine from the perspective of defect chemistry. Silicon diffusion is dominated by V-O (center dot center dot)-associated V(Si)aEuro(3)aEuro(3), whereas oxygen diffusion is dominated by hopping of V-O (center dot center dot) under anhydrous conditions, and by (OH)(O) (center dot) under hydrous conditions. By considering the charge neutrality condition of [(OH)(O) (center dot)] = 2[V(Me)aEuro(3)] in hydrous forsterite and iron-bearing olivine, we get D (Si) ae ()(1/3) and D (O) ae ()(0), which explains the experimental results of water effects on oxygen and silicon self-diffusion rates (Fei et al. in Nature 498:213-215, 2013; J Geophys Res 119:7598-7606, 2014). The dependence of creep rate in the Earth's mantle should be close to that given by Si and O self-diffusion coefficients obtained under water unsaturated conditions.