Elasticity of the pyrope (Mg3Al2Si3O12)-majorite (MgSiO3) garnets solid solution |
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| Authors: | G D Gwanmesia J Liu G Chen S Kesson S M Rigden R C Liebermann |
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| Institution: | (1) Institute of Geochemistry, Mineralogy and Ore Formation, National Academy of Science of Ukraine, Palladin Ave., 34, 03680 Kyiv-142, Ukraine;(2) Applied Geosciences, Technical University of Berlin, 10623 Berlin, Germany;(3) GeoForschungsZentrum, Sektion 4.1, Telegrafenberg, 14473 Potsdam, Germany |
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| Abstract: | Dense isotropic polycrystalline specimens of majorite-rich garnets (Py100, Py62Mj38, Py50Mj50, Py21Mj79 and Mj100) along the pyrope (Mg3Al2Si3O12 = Py100)-majorite (MgSiO3 = Mj100) join were fabricated in a 2000-ton uniaxial split-sphere anvil apparatus (USSA-2000) at pressures from 10 to 18.5 GPa and
temperatures from 1200 to 1850 °C, within their stability fields in runs of 2–4-h duration, using hot-pressing techniques
developed by Gwanmesia et al. (1993). These specimens are single-phased, fine-grained (≤5 mm), free of microcracks, and have
bulk densities greater than 99% of the corresponding single-crystal X-ray density. Elastic compressional (P) and shear (S) wave velocities were determined at room pressure and temperature for these polycrystalline garnet specimens by phase comparison
ultrasonic interferometry. For Mj100, the P and S wave velocities are within 1% of the Hashin-Shtrikman averages calculated from the single crystal elastic moduli measured
by Brillouin spectroscopy. Both the elastic bulk modulus (K) and the shear modulus (G) decrease continuously with increasing majorite content from pyrope garnet (Py100) to pure majorite garnet (Mj100). The compositional dependence of K and G are given by K = 172.3 (40) − 0.085X, and G = 91.6 (10) − 0.038X, where X = mol% majorite), respectively, indicating that substitution of Si for Mg and Al decreases both K and G by about 5% along the solid solution series.
Received: 25 March 1999 / Accepted: 12 July 1999 |
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| Keywords: | Garnets Polycrystals Hot-pressing Elasticity Interferometry |
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