HR: 08:00h
AN: MR41A-01 INVITED     [Abstracts]
TI: New Constraints on the Earth's Core Chemical Composition
AU: * Fiquet, G
EM: fiquet@lmcp.jussieu.fr
AF: Laboratoire de Min{\'e}ralogie et Cristallographie, Universit{\'e} Paris 6 Institut de Physique du Globe de Paris 140 rue de Lourmel, Paris, 75015 France
AU: Badro, J
EM: james.badro@lmcp.jussieu.fr
AF: Laboratoire de Min{\'e}ralogie et Cristallographie, Universit{\'e} Paris 6 Institut de Physique du Globe de Paris 140 rue de Lourmel, Paris, 75015 France
AU: Guyot, F
EM: guyot@lmcp.jussieu.fr
AF: Laboratoire de Min{\'e}ralogie et Cristallographie, Universit{\'e} Paris 6 Institut de Physique du Globe de Paris 140 rue de Lourmel, Paris, 75015 France
AB: In the last forty years, there has been a considerable debate about which light element among sulfur, silicon, oxygen, carbon or hydrogen should be in the core [Poirier, {\it Phys. Earth Planet. Int.}, {\bf 85}, 319, 1994]. Not only the nature of these elements is a standing problem of prime importance, since it conditions the existence of a freezing point depression at the inner core boundary, but also their distribution within the core is unknown. It is indeed crucial to determine to what extent light elements are released in the liquid outer core, thus inducing solutal convection which in turn contributes to power the geodynamo [Loper, {\it J. R. Astron. Soc.}, {\bf 54}, 389, 1978]. In this respect, density and sound velocity measurements at high pressure in solid iron alloyed with different light elements are important to constrain core dynamics and coupling between liquid outer core and solid inner core. However, sound velocity data were not available until very recently, with sound velocity measurement in iron at high pressure [Fiquet et al.; {\it Science}, {\bf 291}, 468, 2001; Mao et al., {\it Science}, {\bf 292}, 914, 2001; Antonangeli et al., {\it Earth Planet. Sci. Lett.}, {\bf 225}, 243, 2004]. The question now is how to constrain the relative abundance of these light elements, and eventually rule out some of them based on a confrontation of seismic and mineralogical data. Here, we report direct measurements of acoustic sound velocity in iron alloyed with light elements supposedly entering in the composition of the Earth's core, {\it i.e.} oxygen, sulfur and silicon, and address the question of the composition of the core. In this work, we measured longitudinal sound velocities in light-element alloys of iron (FeS, FeO, FeS$_{2}$, and FeSi) at high pressure by inelastic X-ray scattering. This data set provides a new mineralogical constraint on the composition of the Earth's core, and completes the previous set formed by compressibility and density measurements for these compounds. The combination of these data sets and their comparison with the reference Earth models derived from seismology allows us to determine an average composition of the Earth's core.
DE: 5109 Magnetic and electrical properties
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 1025 Composition of the mantle
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting