HR: 0800h
AN: MR41A-0902    [Abstracts]
TI: Effect of Hydrogen on Mg-Fe Interdiffusion in Ferro-periclase
AU: * Demouchy, S
EM: demou005@umn.edu
AF: Lunar and Planetaray Instit., 3600 Bay Area Blvd, Houston, TX 77058 United States
AU: * Demouchy, S
EM: demou005@umn.edu
AF: University of Minnesota, Dept. Geology and Geophysics 310 Pillsbury Drive, Minneapolis, MN 55455 United States
AU: Mackwell, S J
EM: mackwell@lpi.usra.edu
AF: Lunar and Planetaray Instit., 3600 Bay Area Blvd, Houston, TX 77058 United States
AU: Kohlstedt, D L
EM: dlkohl@umn.edu
AF: University of Minnesota, Dept. Geology and Geophysics 310 Pillsbury Drive, Minneapolis, MN 55455 United States
AB: Physical properties of minerals in Earth's mantle are substantially modified by interaction with volatiles, such as hydrogen. Recently, ionic diffusion in olivine has been shown to be significantly faster in the presence of hydrogen^1,2. Another important mineral in Earth's interior is ferro-periclase, (Mg,Fe)O, the second most abundant mineral in the lower mantle. We report here on an experimental investigation of Mg-Fe interdiffusion in ferro-periclase under hydrous conditions. Annealing experiments under hydrous condition were performed using a gas-medium pressure vessel (Paterson apparatus) at a confined pressure of 300 MPa over a temperature range of 1000 to 1250°C. The diffusion couples consisted of two (111) single crystal plates, one with a composition of MgO and one of (Mg_0.72Fe_0.28)O. Each diffusion couple was placed in a Ni can, which controls the oxygen fugacity, together with MgO and Mg(OH)₂ powders. We quantified the Mg and Fe diffusion profiles with an electron microprobe. The interdiffusion coefficient was calculated from the Fe concentration as a function of position in the sample using the Boltzmann-Matano analysis. For a composition of (Mg_0.9Fe_0.1)O, our results indicate that Fe-Mg interdiffusion is approximately a factor of 4 faster under hydrous conditions than under anhydrous conditions^3,4. This enhanced rate of interdiffusion is attributed to the increased concentration of metal vacancies resulting from the incorporation of hydrogen ions into the ferro-periclase lattice. References 1. Chakraborty, S. and Costa, F. (2004). Fast diffusion of Si and O in San Carlos olivine under hydrous conditions. Geochim.t Cosmochim. Acta 68, A275. 2. Hier-Majumber, S., Anderson, I.M., and Kohlstedt, D.L., 2004, Influence of Protons on Fe-Mg interdiffusion in olivine: J. Geophys. Res., 110, doi: 10.1029/2004JB003292. 3. Holzapfel, C., Rubie, D.C., Mackwell, S.J., and Frost, D.J., 2003, Effect of pressure on Fe-Mg interdiffusion in (Fe_xMg_{1-x})O, ferropericlase: Phys. Earth Planet. Inter., 139, 21-34. 4. Mackwell, S.J., Bystricky, M., and Sproni, C., 2005, Fe-Mg interdiffusion in (Mg,Fe)O: Phys. Chem. Mineral., 4. Mackwell, S.J., Bystricky, M., and Sproni, C., 2005, Fe-Mg interdiffusion in (Mg,Fe)O: Phys. Chem. Mineral., 78, doi:10.1007/S0026900500136.}
DE: 1025 Composition of the mantle
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3900 MINERAL PHYSICS
DE: 3904 Defects
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005