Acoustic wave velocities for synthetic polycrystalline pyrope (Mg3Al2Si3O12) were measured to 9 GPa and temperatures up to 1000 degrees C by ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a cubic-anvil DIA-type apparatus (SAM-85). Specimen lengths at high pressures (P) and temperatures (7) are directly measured by X-radiographic methods. Elastic wave travel times and X-ray diffraction data were collected after heating and cooling at high pressures to minimize effect of non-hydrostatic stress on the measurements. A linear fit to the high P and T data set yields the elastic bulk and shear moduli [K-S = 175 (2) GPa; G = 91 (1) GPa] and their pressure and temperature derivatives [K'(S) = 3.9 +/- 0.3; G' = 1.7 +/- 0.2 and (delta K-S/delta T)(P) = -18 (2) MPa/K; (delta G/delta T)(P) = -10 (1) MPa/K]. In a separate analysis, the pressure-volume-temperature data collected during these acoustic experiments were fit to a high temperature Birch-Murnaghan (HTBM) equation [with K' fixed at 3.9] and to each isothermal P-V-T data yielding (delta K-T/delta T)(P) = -22 (2) MPa/K and (delta K-T/delta T)(P) = -20 (5) MPa/K, respectively. Comparison of Py100 data with those other Py-Mj compositions indicates that the thermo elastic properties are insensitive to majorite content in the garnet along the pyrope-majorite join. (c) 2005 Elsevier B.V. All rights reserved.
Delaware State Univ, Dept Phys & Pre Engn, Dover, DE 19901 USA; Stony Brook Univ, Inst Mineral Phys, Stony Brook, NY 11974 USA; Stony Brook Univ, Dept Geosci, Stony Brook, NY 11974 USA; Lab Phys Globe Paris, Dept Geomat, Paris, France; Los Alamos Natl Lab, Los Alamos, NM 87545 USAArticleEnglish