HR: 0800h
AN: T41B-1183    [Abstracts]
TI: Influence of Protons on Fe-Mg Interdiffusion in Olivine
AU: * Hier-Majumder, S
EM: saswata.hier-majumder@yale.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Anderson, I M
EM: andersonim@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Kohlstedt, D L
EM: dlkohl@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AB: In this work, we present experimental quantification of the influence of water-derived protons on Fe-Mg interdiffusion in olivine. We carried out interdiffusion experiments on diffusion couples consisting of oriented single crystals of olivine of composition $\mathrm{Fo_{90}}$ and $\mathrm{Fo_{80}}$. The diffusion anneals were performed between pressures 0.1 and 6 GPa at temperatures of 1373 to 1450 K. The oxygen fugacity during the anneals was set by the Ni-NiO solid state reaction. We report diffusivity as a function of temperature, pressure, and water fugacity following the relation \[ \tilde{D}_{\mathrm{Fe-Mg}} = D_{o} \left( f_{\mathrm{H_2O}}/f_{\mathrm{H_2O}}^o\right)^r \exp{\left[-(Q + PV^*)/{\mathrm{R}T}\right]} \] where $\log{(D_o)} = (-14.8\pm2.7) \log( \mathrm{m^2 s^{-1} })$ , $r = 0.9\pm0.3$, $Q = 220\pm60$ kJ/mol, and $V^* = \left(16\pm6\right) \times 10^{-6}\mathrm{m^3 /mol}$. The water fugacity exponent of 0.9, which is approximately the same as that for hydroxyl solubility in olivine [{\it{Kohlstedt et al.}}, 1996], indicates that octahedral cation vacancies form defect associates with water-derived protons. Based on our results, cation diffusion in water-saturated olivine is $\sim$50 times faster than under water-absent conditions at a pressure of 5 GPa and a temperature of 1373 K.
DE: 3620 Crystal chemistry
DE: 3904 Defects
DE: 3914 Electrical properties
DE: 3924 High-pressure behavior
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting