HR: 08:15h
AN: MR21A-02    [Abstracts]
TI: A new Model for Oxygen Solubility in Liquid Iron and the Oxygen Content of the Cores of Earth and Mars
AU: * Rubie, D C
EM: dave.rubie@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D-95440 Germany
AU: Frost, D J
EM: dan.frost@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D-95440 Germany
AU: Asahara, Y
EM: yuki.asahara@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D-95440 Germany
AU: Langenhorst, F
EM: falko.langenhorst@uni-jena.de
AF: Institut fuer Geowissenschaften, Friedrich-Schiller-Universitaet, Jena, D-07749 Germany
AB: Oxygen has been proposed as being an important light element in the Earth's core. In order to test this hypothesis, the solubility of oxygen in liquid Fe at P-T conditions of the core and the partitioning of oxygen between silicates and Fe under core formation conditions must be known. According to our recent study (Rubie et al. 2004, Nature 429, 58), the solubility of oxygen in liquid Fe-Ni alloy increases with temperature but decreases with pressure in the P-T range 5-23 GPa and 2100-2700 K. Based on a simple thermodynamic model in which ΔV (the volume change for reaction between silicate/oxide, Fe and O) is constant, extrapolations of the data to core conditions suggest that the amount of O in the Earth's core is close to zero. New data are now available, both at low pressures (2-25 GPa) from our group and at much higher pressures (25-97 GPa) from diamond anvil cell experiments (Takefuji et al. 2005, GRL 32, L06313). The combined data sets show that the pressure dependence of O solubility in liquid Fe changes from negative at low pressures to positive at higher pressures (>15 GPa). Using these experimental data we have developed a more sophisticated thermodynamic model in which both the partial molar volume and compressibility of FeO in liquid Fe are considered. The associated solution model uses Fe, FeO and FeO_1.5 as liquid species whose activities are determined using 1 bar phase relations in the Fe-O system. An equation of state estimate for liquid Fe alloy is then determined using the high-pressure data. We find that reasonable values for the volume and bulk modulus of the metal liquid can produce the minimum in oxygen solubility that is suggested by the experimental data. This new solubility model is consistent with the core formation models of Rubie et al. (2004) that explain the different FeO contents of the mantles of Earth and Mars. In addition, extrapolating the model to core pressures indicates that oxygen must be an important light element in the Earth's core, but not in the Martian core.
DE: 1015 Composition of the core
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3924 High-pressure behavior
DE: 5430 Interiors (8147)
DE: 6225 Mars
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005