HR: 0800h
AN: MR11A-0903    [Abstracts]
TI: Single Crystal Elastic Constants From Surface-Wave Measurements on Petrologic Thin-sections
AU: Gauvin, M
EM: melanie.gauvin@ens-lyon.fr
AF: Laboratorie de Sciences de la Terra, Ecole Normale Superieure de Lyon 46 Alee d'Italie Cedex 07, Lyon, 69346 France
AU: * Brown, J M
EM: brown@ess.washington.edu
AF: Earth and Space Sciences, University of Washington Box 351310, Seattle, WA 98195 United States
AU: Abramson, E H
EM: evan@ess.washington.edu
AF: Earth and Space Sciences, University of Washington Box 351310, Seattle, WA 98195 United States
AU: Newman, J
EM: newman@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, Colllege Station, TX 77843 United States
AU: Carlson, R L
EM: carlson@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, Colllege Station, TX 77843 United States
AB: Although single-crystal elastic constants for many common rock-forming minerals have been measured, significant gaps remain in mineral databases. Several authors have noted a continuing need to estimate mineral properties in order to compare seismic profiles with petrologically constrained elastic models for the crust and mantle. In part, the problem is associated with the difficulty of obtaining samples of sufficient size and quality to undertake laboratory studies. The solution suggested here makes use of samples within standard petrologic thin-sections. Individual single crystals within the section are oriented using electron backscattered diffraction (EBSD). Compositions are determined from standard microprobe analytic techniques. The Impulsive Stimulated Light Scattering method allows measurement of surface-wave velocities as a function of direction in the plane of the thin section. Velocities from several crystals of the same composition but with differing orientations relative to the thin section are inverted to determine the single crystal elastic constants tensor. An advantage of this method is the ability to work with many small and homogeneous crystals (as small as 50 microns) that can be prepared simultaneously using standard petrological techniques. The surface finish necessary for the EBSD analysis is sufficient for the acoustic measurements. Working with light back scattered from the surface removes the difficulty with previous light-transmission methods (Brillouin and ISLS) that required nearly imperfection-free crystals. Although surface waves have a strong dependence on shear elastic constants, the elliptical particle motion couples velocities to all elastic constants. Plagioclase-group minerals constitute 30% or more of the oceanic crust and a larger fraction of the continental crust. Only pseudo-single-crystal (monoclinic) properties have been reported for these triclinic minerals. We report results obtained on individual single crystals that allow investigation of the full elastic tensor. Extension of the work to high pressure is possible.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 5102 Acoustic properties
DE: 3909 Elasticity and anelasticity
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting