HR: 1330h
AN: T42A-0273    [PDF]
TI: Compositional effect on the dihedral angle between olivine and Fe-S liquid up to 20 GPa: Possibility of percolative core formation
AU: * Terasaki, H
EM: Hidenori.Terasaki@Uni-Bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Universitaetsstrasse 30, Bayreuth, 95440 Germany
AU: Rubie, D C
EM: Dave.Rubie@Uni-Bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Universitaetsstrasse 30, Bayreuth, 95440 Germany
AU: Frost, D J
EM: Dan.Frost@Uni-Bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Universitaetsstrasse 30, Bayreuth, 95440 Germany
AU: Langenhorst, F
EM: Falko.Langenhorst@Uni-Bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Universitaetsstrasse 30, Bayreuth, 95440 Germany
AB: The separation of liquid metal from a crystalline silicate mantle during planetary core formation could have only operated to completion if the liquid metal fraction formed an interconnected network. Interconnectivity depends on the dihedral angle between liquid metal and crystalline silicates at low melt fractions. Gaetani and Grove (1999) showed that liquid Fe-alloy can wet an olivine matrix at high O and S fugacities at ambient pressure. Therefore, it is important to understand the effects of the compositions of Fe alloy and the silicate phase on the dihedral angle behaviour systematically under high pressure conditions. The result is also applicable to core formation mechanisms on other terrestrial planets. For example, the Martian mantle is believed to be more Fe-rich and the Martian core more sulphur-rich compared to the Earth, which may have resulted in important differences in silicate-liquid metal dihedral angles during core formation. We have investigated the effects of the metallic and silicate phase compositions on the dihedral angle up to 20 GPa and 2200 K by varying the sulphur content of an Fe-S alloy (S = 22 $\sim$ 50 at.%) and the FeO content of a coexisting olivine assemblage (FeO = 0 $\sim$ 67 mol.%). Using a multianvil apparatus, experiments at high pressure and temperature were performed for 12 hours, which corresponds to the time scale for textural equilibration. Graphite was used as the capsule material. In the olivine stability field, texturally equilibrated dihedral angles decrease with increasing sulphur content and decrease dramatically with increasing FeO content of olivine. Increasing the FeO content of olivine results in an increase in both the oxygen fugacity and oxygen solubility in the sulphide melt. Dihedral angles also decrease slightly with increasing temperature. The minimum value determined for the dihedral angle between iron-sulphide and olivine was $65\deg$, which is still slightly higher than the critical angle for wetting of $60\deg$. These results show that melting of the silicate is required to obtain complete metal-silicate separation and therefore support a magma ocean scenario during core formation.
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 5114 Permeability and porosity
DE: 8125 Evolution of the Earth
DE: 8147 Planetary interiors (5430, 5724)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting