It was noted that the limited stability range of wadsleyite impeded attempts to

constrain kinetic parameters (e.g. activation energy, activation volume) by using

experiments carried out over wide ranges of temperature and pressure. New

measurements were carried out here in order to extend the experimental

temperature range of the dataset of Chakraborty et al. (1999) to the maximum

possible limit for the given experimental setup. This permitted the obtention of a

better constrained value (about 230kJ/mol) for the activation energy for Fe–Mg

diffusion in wadsleyite at 15GPa and permitted the characterization of the

compositional dependence of Fe–Mg diffusion in wadsleyite. Evaluation of all of

the published data revealed that there was a strong pressure-dependence of the

diffusion coefficient, with an activation volume of ≈14cm3/mol. The expression,

D(m2/s) = 1.24 x 10-6exp[11.8(0.86-XMg)]exp[{-229000+13900(P-15)(J/mol)}/RT]

gave an excellent description of all of the experimentally measured diffusion

coefficients in wadsleyite and indicated a consistency between various studies

performed used differing methods. The expression was expected to provide a firm basis for extrapolating diffusion data for wadsleyite to conditions removed from

the experimental ones.

Fe–Mg Interdiffusion in Wadsleyite: the Role of Pressure, Temperature and

Composition and the Magnitude of Jump in Diffusion Rates at the 410km

Discontinuity. C.Holzapfel, S.Chakraborty, D.C.Rubie, D.J.Frost: Physics of the

Earth and Planetary Interiors, 2009, 172[1-2], 28-33