Fe-Mg interdiffusion in olivine and implications for chemical heterogeneity in the upper mantle

The kinetics of Fe-Mg interdiffusion in nominally dry polycrystalline olivine was investigated at 6 GPa and 1373‒1673 K using diffusion couples of forsterite (Fo100) and olivine (Fo90) aggregates. Diffusion profiles were measured by electron microprobe, and diffusion data were analyzed by the Boltzmann-Matano method. Our results show that the Fe-Mg interdiffusion coefficient (DFe-Mg) depends on the iron content (with XFe ranging from 0 to 0.1). The temperature dependence of DFe-Mg in olivine can be described by the Arrhenius relation. By combining the present data and a simple model, it is found that the length scale over which the chemical heterogeneities are homogenized by Fe‐Mg interdiffusion in the upper mantle is very limited at the geological time scale, only through solid-state diffusion.