Effect of pressure on Fe-Mg interdiffusion in (FexMg1-x)O, ferropericlase

Fe-Mg interdiffusion in ferropericlase has been studied at pressures between 8 and 23 GPa and temperatures between 1653 and 2073 K, using a multianvil apparatus. The compositions of the single crystal diffusion couples were X-FeO = 0.07 for one crystal and X-FeO = 0.37 for the other, although in one case pure MgO was used instead Of X-FeO = 0.07. Fe-Mg interdiffusion at oxygen fugacities buffered by Ni-NiO, including I bar data at 1673 and 1873 K of Mackwell et al. (in preparation), can be described for 0.07 < X-FeO < 0.37 by: DFe-Mg = D-0 exp(AX(FeO)/RT) exp (-E-A + VAP/RT) where the pre-exponential factor D-0 = 9.8(+/-0.7) X 10(-6) m(2) s(-1), the constant A = 132 +/- 13 kJ mol(-1), the activation energy E-A = 255 +/- 16 kJ mol(-1), the activation volume V-A = 3.3 +/- 0.1 cm(3) mol(-1), X-FeO is mole fraction of FeO in (FexMg1-x)O, T is absolute temperature, and P is pressure. This result can be used to constrain Fe-Mg interdiffusion coefficients of ferropericlase in the Earth's lower mantle. At the top of the lower mantle, at 23 GPa and 2000 K, diffusivities will be 0.5 x 10(-13) m(2) s(-1) and 1.1 X 10(-13) m(2) s(-1) for X-FeO = 0.1 and 0.2, respectively. Extrapolating the results to higher pressures suggests that diffusive interaction at the core-mantle boundary will extend at most similar to15 km into the lower mantle. (C) 2003 Elsevier B.V. All rights reserved.