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 (Fe_0.5,Mg_0.5)O samples by electron microprobe analysis, and the Fe-Mg interdiffusivities were determined as D_Fe-Mg=D₀exp{−E*(1+PV*_Mg/E*_Mg)/RT}, where D₀=4.1(^+16.1_−3.3)×10⁻⁷ m²/s, E*=(1−C_Mg)E*_Fe+C_MgE*_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.