HR: 13:52h
AN: MR23D-02    [Abstracts]
TI: Iron partitioning and the self-oxidation of the lower mantle
AU: Auzende, A
EM: auzende@impmc.jussieu.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Mineralogie, 140 rue de Lourmel, Paris, 75015, France
AU: * Badro, J
EM: badro@ipgp.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Mineralogie, 140 rue de Lourmel, Paris, 75015, France
AU: * Badro, J
EM: badro@ipgp.fr
AF: Lawrence Livermore National Laboratory, IGPP/University of California, Livermore, 94550, United States
AU: Ryerson, F J
EM: ryerson1@llnl.gov
AF: Lawrence Livermore National Laboratory, IGPP/University of California, Livermore, 94550, United States
AU: Fiquet, G
EM: fiquet@impmc.jussieu.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Mineralogie, 140 rue de Lourmel, Paris, 75015, France
AB: Magnesium silicate perovskite (Mg,Fe)SiO₃ (Mg-pv) and ferropericlase (Mg,Fe)O (fp) are the dominant phases in the lower-mantle. Their physical and chemical properties determine the dynamics of the deep Earth. It is thus of prime importance to constrain element partitioning at high pressure for improving the geochemical models of the Earth. We investigated iron partitioning between Mg-pv and fp synthetised under lower-mantle conditions (up to 115 GPa and 2200 K) in a laser heated diamond anvil cell (LH-DAC). Recovered samples were thinned to electron transparency by focussed ion beam (FIB) and characterized by analytical transmission electron microscopy (ATEM) and nanometer scale ion probe (nanoSIMS). Iron concentrations in both phases were obtained from EDX measurements and nanoSIMS. Our results are the first to show that recently reported transitions in the lower-mantle (Badro et al, 2003; Murakami et al., 2004) directly affect the evolution of Fe-Mg partitioning between both phases. Mg-pv is increasingly iron-depleted above 70-80 GPa possibly due to the high spin-low spin transition of iron in fp. Conversely, the perovskite to post-perovskite transition is accompanied by a strong iron enrichment of the silicate phase. Iron concentrations determined by ATEM and nanoSIMS are in excellent agreement. Nanoparticles of metallic iron were observed in the Mg-pv bearing runs (figure), suggesting the disproportionation of ferrous iron and the self-oxidation of the mantle, but were not observed when the post- perovskite (ppv) phase was present. Implications on the oxidation state of the Earth and core segregation will be discussed. References J. Badro, G. Fiquet, F. Guyot, J.-P. Rueff, V.V. Struzhkin, G. Vanko, and G. Monaco, Science 300 789-791 (2003) M. Murakami, K. Hirose, N. Kawamura, N. Sata, and Y. Ohishi, Science 304 855-858 (2004)
DE: 1025 Composition of the mantle
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3621 Mantle processes (1038)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting