Effect of anomalous compressibility on Fe diffusion in ferropericlase throughout the spin crossover in the lower mantle

The transport of iron in the deep earth is important for understanding chemical equilibration between deep earth phases and between the core and mantle. However, iron transport modeling is complicated by its changes in spin state with pressure and temperature. Recent studies (Saha et al., 2011; Ammann et al., 2011) calculated the diffusivity of iron in ferropericlase as a function of ironʹs spin state but did not include the coupling of iron migration energetics to the observed anomalous bulk modulus softening associated with the spin transition (Wentzcovitch et al., 2009; Crowhurst et al., 2008). Here we calculate the diffusivity of iron in ferropericlase throughout the lower mantle using a model for both ironʹs spin and the anomalous bulk modulus softening to provide a complete model of iron diffusion in ferropericlase. Including the bulk modulus softening increases iron diffusivities by a factor of thirty relative to values without this effect at some depths on the geotherm.