Elastic wave velocities at Mg3Al2Si3O13-pyrope garnet to 10 GPa

• Published in: The American mineralogist 1999-03, Vol.84 (3), p.384-388
• Main Authors: Chen, Ganglin, Cooke, Jr, Gwanmesia, Gabriel D, Liebermann, Robert C
• Format: Article
• Language: eng ; jpn
• Subjects: elastic properties; elastic waves; experimental studies; garnet group; Geophysics; high pressure; nesosilicates; orthosilicates; P-T conditions; pressure; pyrope; related to mantle; silicates; velocity
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-1999-0322

Elastic wave velocities of Mg3Al2Si3O12 pyrope garnet were measured to 10 GPa at ambient temperature, using ultrasonic interferometry in a 1000 ton split-cylinder, multi-anvil apparatus (USCA-1000). The sample used in the ultrasonic measurements was a polycrystalline specimen hot-pressed at 5 GPa and 1350°C in a 2000 ton uniaxial split-sphere apparatus (USSA-2000) from a homogeneous glass of pyrope composition. Special P-T paths used during synthesis minimized effects of decompressing and thermal cracking; the bulk density of the sample was indistinguishable from the X-ray density. The elastic wave velocities measured at the ambient condition agree with the Hashin-Shtrikman averages of the single crystal values within the mutual uncertainties. The high-pressure experiments yielded the elastic moduli and their pressure derivatives (finite strain fit) for the shear modulus G0 = 92±1 GPa. G'0 = (θG/θP)T = 1.6±0.2 and for the longitudinal modulus L0 = 294±1 GPa, L'0 = (θL/θP)T = 7.4 ± 0.5, (L = Ks+4/3G), from which the bulk modulus K0 = 171±2 GPa, K'0 = (θKs/θP)T = 5.3±0.4 was calculated. The pressure derivative for the shear modulus of pyrope did not differ from those of natural pyrope-almandine-grossular garnets. For the bulk modulus, the pressure derivative for pyrope agreed with that for pyrope-almandine but was substantially higher (25%) than that for the Ca-bearing garnet. In the pyrope-majorite series, K'0 remained constant, whereas G'0 increased by 25 for 38% majorite content.