Fe–Mg interdiffusion in magnesiowüstite up to 35 GPa

Fe–Mg interdiffusivities in (Fe,Mg)O magnesiowüstite have been measured in experiments conducted at pressures of 7–35 GPa and temperatures of 1573–1973 K using a Kawai-type high-pressure apparatus. The diffusion profiles were measured across the interface between MgO and (Fe0.5,Mg0.5)O samples by electron microprobe analysis, and the Fe–Mg interdiffusivities were determined as DFe–Mg=D0exp{−E*(1+PV*Mg/E*Mg)/RT}, where D0=4.1(+16.1−3.3)×10−7 m2/s, E*=(1−CMg)E*Fe+CMgE*Mg (activation energy for the concentration of Mg, where E*Fe=113(±74) kJ/mol and E*Mg=226(±32) kJ/mol), the activation volume V*Mg=1.8(±1.2)×10−6 m3/mol. By extrapolating these results to the P–T conditions of the core–mantle boundary, we conclude that the interdiffusivity of Fe–Mg in magnesiowüstite at the bottom of the lower mantle is at least one order of magnitude larger than that at the top of the lower mantle.