HR: 1340h
AN: MR43A-0885    [Abstracts]
TI: Interconnectivity of liquid Fe-alloy in planetary mantles
AU: * Terasaki, H
EM: terasaki@mail.tains.tohoku.ac.jp
AF: Faculty of Science, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai, 980-8578 Japan
AU: Frost, D J
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, 95440 Germany
AU: Langenhorst, F
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, 95440 Germany
AU: Rubie, D C
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, 95440 Germany
AB: The most important and fundamental aspect of planetary core formation is whether liquid Fe-alloy can segregate through crystalline silicates. The interconnectivity between silicate minerals (olivine, ringwoodite, garnet, majorite, and Mg-Perovskite) and liquid Fe-S-O has been investigated experimentally. Experiments were carried out using 1200 and 5000 tonne multi-anvil presses. In all experiments, starting powders were mixtures of Fe$_{61}$S$_{39}$ and synthetic silicates that were sealed in graphite capsules. Experimental conditions were 1.5-24.5 GPa, 1650-2200 K, and 5-12 hours duration. Observations of the sample textures were performed using SEM and TEM. The interconnectivity changes significantly with the solubility of light elements, especially oxygen in the Fe-alloy. Dihedral angles are observed to increase with increasing pressure between 1.5-5.0 GPa. This is most likely a result of the drastic decrease in Fe-alloy oxygen solubility with pressure. As a result, interconnected networks can form only up to approximately 3.5 GPa. This indicates that Fe-alloy can percolate through the mantles of small sized bodies such as planetesimals and asteroids at oxidized conditions. Dihedral angles in olivine and ringwoodite assemblages are $103-69\deg$ which is slightly lower (approximately $10\deg$) than that in the garnet and majorite assemblages using the same Fe-alloy composition. For (MgFe)SiO$_{3}$ perovskite, however, variations in composition and dihedral angle are rather complicated. The Fe content in Fe-alloy apparently increases with the Fe content of perovskite most likely as a result of the disproportionation of Fe$^{2+}$ to Fe + Fe$^{3+}$. Fe$^{3+}$/$\Sigma$Fe ratio of up to 0.25 in perovskite coexisting with Fe-S alloy were measured by EELS. The Fe$^{3+}$ content of Pv increases with Fe content of Pv. The additional metal formed dissolves in the Fe-S alloy and increases with the Fe/S ratio. This increase is coupled with a decrease in the dihedral angle. These results show that interconnected networks are limited to relatively small bodies ($\sim$ 1000 km radius) and are not likely to form in the bulk of planetary mantles.
DE: 8439 Physics and chemistry of magma bodies
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8125 Evolution of the Earth
DE: 8147 Planetary interiors (5430, 5724)
DE: 5460 Physical properties of materials
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting