Pressure induced spin transition and its effects on diffusion of Fe2+ in ferropericlase

Fe cation diffusion plays a fundamental role for many processes in Earth’s mantle involving chemical, isotopic and advective mass transfer, and can potentially control homogenization of mantle materials and equilibration of elements between the core and mantle. Present data on Fe transport in Fp is limited to pressures below the top of the lower mantle and therefore must be extrapolated to model lower mantle conditions. However, extrapolation of Fe diffusion properties from measurements under 35 GPa to lower mantle pressures is quite uncertain due to uncertainty in the Fe activation volume and its unknown pressure dependence. In particular, the existing diffusion data includes no information on the effect of the recently discovered Fe spin transition. In the present study we combine first principles methods with statistical diffusion models to compute the Fe2+ diffusivity in dilute Fe ferropericlase at lower mantle pressures and temperatures. Diffusivities are determined for pure high- and low-spin Fe2+, as well as the mixed spin state which exists throughout much of the lower mantle. The results are compared with existing experimental diffusion data and possible implications for lower mantle properties are discussed.