HR: 0800h
AN: U11A-0001    [Abstracts]
TI: A Tightly Constrained Composition Model of Earth's Core
AU: * Badro, J
EM: badro@ipgp.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Minéralogie, 140 rue de Lourmel, Paris, 75015, France
AU: Fiquet, G
EM: fiquet@impmc.jussieu.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Minéralogie, 140 rue de Lourmel, Paris, 75015, France
AU: Guyot, F
EM: guyot@impmc.jussieu.fr
AF: Institut de Physique du Globe de Paris, IMPMC, Minéralogie, 140 rue de Lourmel, Paris, 75015, France
AB: We measure compressional sound velocities in light-element alloys of iron (FeO, FeSi, FeS, and FeS₂) at high pressure in the diamond anvil cell. Combining this data set with pressure-density (equation of state) systematics, and constraining them with radial seismic models, we propose an average composition model of Earth's inner core that matches both the seismically observed densities and compressional sound speeds. We show that sulphur cannot be the only light alloying element in the core, because it cannot satisfy all at once the needed density, sound velocity, and abundance (from cosmochemical models). On the other hand, the incorporation of silicon or oxygen is compatible with geophysical observations and geochemical abundances. We therefore propose a preferred model, where the inner core contains 2.3 wt% silicon and traces of oxygen, whereas the outer core contains 5.3 wt% oxygen and 2.8 wt% silicon. Our model is in excellent agreement with recent high-pressure silicon solubility data in molten iron. Our model's oxygen-content in the outer core is constrained by high-pressure oxygen solubility data in molten iron. Our compositional model is constrained by seismology, petrology, and mineral physics. Using existing solubility data, we can infer a range of equilibration parameters that provide as many constraints to the pressure- temperature conditions as well as the depth at the base of the magma ocean during core formation. References N. Takafuji, K. Hirose, M. Mitome, Y. Bando, Solubilities of O and Si in liquid iron in equilibrium with (Mg,Fe)SiO3 perovskite and the light elements in the core, Geophys. Res. Lett. 32 (2005). T. Sakai, T. Kondo, E. Ohtani, H. Terasaki, N. Endo, T. Kuba, T. Suzuki, T. Kikegawa, Interaction between iron and post- perovskite at core-mantle boundary and core signature in plume source region, Geophys. Res. Lett. 33 (2006). J. Badro, G. Fiquet, F. Guyot, E. Gregoryanz, F. Occelli, D. Antonangeli, M. d'Astuto, Effect of light elements on the sound velocities in solid iron: Implications for the composition of Earth's core. Earth Planet. Sci. Lett. 254, 233 (2007).
DE: 1015 Composition of the core
DE: 1065 Major and trace element geochemistry
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
SC: Union [U]
MN: 2007 Fall Meeting