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Sound velocities in MgSiO 3 ‐garnet to 8 GPa
Author(s) -
Gwanmesia Gabriel D.,
Chen Ganglin,
Liebermann Robert C.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1998gl900189
Subject(s) - pyrope , bulk modulus , mineralogy , shear modulus , geology , materials science , analytical chemistry (journal) , shear waves , isotropy , crystallite , elastic modulus , grossular , shear (geology) , composite material , optics , physics , chemistry , metallurgy , chromatography , quartz
Velocities of acoustic compressional (P) and shear (S) waves were measured to 8 GPa at room temperature for dense (99.7% of theoretical density), isotropic polycrystalline specimens of MgSiO 3 ‐majorite garnet using the phase comparison method of ultrasonic interferometry in a 1000‐ton split‐cylinder apparatus (USCA‐1000). The pressure derivatives of the adiabatic bulk modulus (K S ) and the shear modulus (G) are K o ′ = (∂Ks/∂P) T =6.7±0.4 and G o ′ = (∂G/∂P) T =1.9±0.1. Substitution of Si for Mg and Al in these garnets increase K o ′ by 26%, and G o ′ by 16%, from Mg 3 Al 2 Si 3 O 12 ‐pyrope to majorite. The high values of K o ′ and G o ′ from this study lead to much steeper velocity‐depth profiles in the transition zone (400–700 km) than those calculated from the K o ′ and G o ′ estimates from elasticity systematics by Duffy and Anderson (1989).