HR: 0800h
AN: MR31A-0119    [Abstracts]
TI: Elastic Constants of Brucite (Mg(OH)₂) and Diaspore (AlO(OH)) to 12 GPa by Brillouin Scattering
AU: Jiang, F
EM: fumingj@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Speziale, S
EM: speziale@uclink.berkeley.edu
AF: University of California, Berkeley, Department of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720 United States
AU: Majzlan, J
EM: Juraj.Majzlan@minpet.uni-freiburg.de
AF: Albert-Ludwig-University of Freiburg, Institute of Mineralogy, Petrology and Geochemistry, Albertstrasse 23b, Freiburg, D-79104 Germany
AU: * Duffy, T S
EM: duffy@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AB: Hydroxides such as brucite, Mg(OH)₂, and diaspore, AlO(OH), serve as analogs for the more complex hydrogen-bearing minerals found in subduction zones. The single-crystal elastic constants of these two minerals were determined by Brillouin scattering up to 12 GPa in a diamond anvil cell. A 16:3:1 methanol-ethanol-water and 4:1 methanol-ethanol mixture were used as pressure media and ruby as pressure calibrant. Two platelets of brucite and three platelets of diaspore were measured at room pressure and over nine elevated pressures. Brillouin spectra were recorded in 37 directions with a 5-degree step for each plane. All individual elastic stiffness constants were retrieved by fitting the velocity data to the Christoffel­_s equation. The individual elastic constants, aggregate bulk and shear moduli, were then fitted to the finite Eulerian stain equations to obtain their pressure derivatives. For brucite, aggregate moduli and their pressure derivatives are K_T0=35.9(9) GPa, G_O=31.3(2) GPa, (∂ K_t/∂ P)_T0=8.9(3), (∂ G/∂ P)_O=4.33(4) for the Reuss bound. Diaspore aggregate moduli and their pressure derivatives are K_T0=147.0(7) GPa, G_O=114.8(5) GPa, (∂ K_s/∂ P)_T0=4.1(1), (∂ G/∂ P)_O=1.6(1). For diaspore, both individual and aggregate elastic moduli define nearly linear modulus pressure trend within the measured pressure range. For Brucite, there are clear deviations from linear modulus - pressure trends. In comparison with diaspore, brucite exhibits strong anisotropy. The ratio of the linear compressibility of brucite along the c and a axes decreased from 4.7 to 1.3 over the examined pressure range. The shear anisotropy (C₆₆/C₄₄) decreased from 2.6 at ambient condition to 1.3 with increase of pressure to 12 GPa. Compression curves constructed from our Brillouin data for both brucite and diaspore are in good agreement with previous x-ray diffraction data.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005