HR: 17:45h
AN: MR44A-08    [Abstracts]
TI: Single-crystal Elasticity of Zoisite Ca₂Al₃Si₃O₁₂(OH) by Brillouin Scattering
AU: * Mao, Z
EM: zhumao@princeton.edu
AF: Princeton University, Geosciences Department,Guyot Hall, Princeton, NJ 08544 United States
AU: Jiang, F
EM: fumingj@princeton.edu
AF: Princeton University, Geosciences Department,Guyot Hall, Princeton, NJ 08544 United States
AU: Duffy, T S
EM: duffy@princeton.edu
AF: Princeton University, Geosciences Department,Guyot Hall, Princeton, NJ 08544 United States
AB: Zoisite, Ca ₂Al₃Si₃O₁₂(OH), is an important metamorphic mineral and one of the main H₂O-containing phases minerals in subduction zones. Experiments in basaltic compositions have shown that zoisite can remain stable to pressures of ~3.1 GPa at 650°C (Forneris and Holloway, 2003), and it is stable to ~7 GPa and 1000°C in the calcium-aluminum-silicon-hydrogen system (Poli et al, 1998). The bulk modulus of zoisite was measured by X-ray diffraction in both multi-anvil apparatus and diamond anvil cells (Holland et al, 1996; Comodi et al, 1997; Pawley et al, 1998; Grevel et al, 2000). However, existing results show large discrepancies. That cannot be explained by presence of small amounts of Fe. In order to provide reliable elastic moduli, the single-crystal elastic constants of zoisite were determined by Brillouin spectroscopy. Three platelets were cut from a gem-quality zoisite sample. Single-crystal x-ray diffraction was performed at x17C of Brookhaven National Laboratory. The lattice parameters are a=16.207(5), b=5.540(5), c=10.056(2) Å with a calculated density 3.343(3)g/cm³. The Brillouin spectra were recorded in a forward scattering geometry at ambient conditions. Measurements were made in a total of 37 directions in each plane. The data were inverted for 9 elastic tensor components and 9 crystal orientation parameters. The single crystal elastic tensor constants C₁₁, C₁₂, C₁₃, C₂₂, C₂₃, C₃₃, C₄₄, C₅₅, C₆₆ are 279.1(8), 95.1(18), 91.3(16), 249.3(8), 30.9(8), 216.5(8), 51.6(4), 80.2(4), 65.9(3)GPa respectively. The resulting bounds on the adiabatic bulk and shear moduli are 127.9(4) and 72.6(2)GPa respectively. Our results are generally consistent with previous static compression studies although we obtain higher c axis compressibility than some X-ray studies. Compared with the elastic moduli of lawsonite, zoisite has a similar bulk modulus (~125 GPa), but a 30% larger shear modulus than lawsonite (~52 GPa) (Sinogeikin et al, 2000). The V_P/V_S ratio is 1.76 for zoisite and compared with1.45 for lawsonite. The role of structure and water content in explaining the different properties of the two minerals will be explored.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3900 MINERAL PHYSICS
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005