HR: 11:05h
AN: T21F-04    [PDF]
TI: Sound Velocity Measurements in Textured hcp-Iron and the Anisotropy and Structure of Earth's Inner Core
AU: * Antonangeli, D
EM: antonangeli@esrf.fr
AF: European Synchrotron Radiation Facility, 6 rue Jules Horowitz B.P. 220, Grenoble, 38043 France
AU: Occelli, F
EM: occelli1@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, L-364, Livermore, CA 94551-9900 United States
AU: Badro, J
EM: james.badro@ens-lyon.fr
AF: Laboratoire de Min\'{e}ralogie-Cristallographie, Universit\'{e} Paris VI, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AU: Requardt, H
EM: requardt@esrf.fr
AF: European Synchrotron Radiation Facility, 6 rue Jules Horowitz B.P. 220, Grenoble, 38043 France
AU: Fiquet, G
EM: fiquet@lmcp.jussieu.fr
AF: Laboratoire de Min\'{e}ralogie-Cristallographie, Universit\'{e} Paris VI, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AU: Krisch, M
EM: krisch@esrf.fr
AF: European Synchrotron Radiation Facility, 6 rue Jules Horowitz B.P. 220, Grenoble, 38043 France
AB: Seismological studies show that the Earth's inner core is elastically anisotropic. The anisotropy has an axial symmetry and an amplitude of about 3-4%, with the fast direction oriented parallel to the Earth's rotation axis. Several hypotheses have been proposed to explain this feature, but the lack of evidence from mineral physics does not allow to address them.\\ Indeed, the experimental determination of sound velocity anisotropy in hcp-iron, the main constituent of the inner core, is of primary importance. Studies include first-principle calculations [1-5] and x-ray radial diffraction measurements [6], but the results show general disagreement, not only in magnitude, but in direction as well.\\ We will report new inelastic x-ray scattering (IXS) data on polycrystalline hcp-iron as a function of pressure, complementing and extending previous IXS data [7]. The derived longitudinal and transverse sound velocities will be compared with the calculations and the experimental results present in literature.\\ Furthermore, the issue of elastic anisotropy will be addressed. Taking advantage of the texturing developed by uniaxially compressed hcp-metals [8], and making use of a properly designed diamond anvil cell characterized by an angular aperture of more than \begin{math} 90^{o} \end{math}, we measured the sound velocity at 22 and 112 GPa in two different geometries with respect to the compression axis, probing the longitudinal sound propagation at \begin{math} 50^{o} \end{math} and \begin{math} 90^{o} \end{math} with respect to it. A difference in acoustic sound velocity of about 5% has been detected at the highest pressure. This effective anisotropy on a textured polycrystalline sample is comparable with the one observed in the Earth, further relaxing the requirement of a nearly perfect alignment of iron crystal grains sustained by previous theoretical investigations [1,4]. [1] L. Stixrude, R.E. Cohen, Science 267, 1972 (1995). [2] P. Soderlind et al., Phys. Rev. B 53, 14063 (1996). [3] R. E. Cohen et al., Phys. Rev. B 56, 8575 (1997). [4] G. Steinle-Neumann et al., Phys. Rev. B 60, 791 (1999). [5] G. Steinle-Neumann et al., Nature 413, 57 (2001). [6] H.K. Mao et al., Nature 396, 741 (1998); correction Nature 399, 280 (1999). [7] G. Fiquet et al., Science 291, 468 (2001). [8] H. R. Wenk et al., Nature 405, 1044, (2000).
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8194 Instruments and techniques
SC: Tectonophysics [T]
MN: 2003 Fall Meeting