Elasticity of six polycrystalline silicate garnets at pressure up to 3.0 GPa

Abstract

The elasticities of six polycrystalline silicate garnets (almandine, grossular, pyrope, uvarovite, andradite, and Prp 25 Alm 56 Spe 19 ) have been experimentally studied at pressures up to 3.0 GPa using a phase comparison method with an ultrasonic interferometer in a liquid cell piston-cylinder apparatus. Complete elasticity data sets (P- and S-wave velocities, bulk moduli K s , shear moduli G, and their first pressure derivatives K S ′ and G ′) have been obtained for all six garnets, and are used together with an up-to-date compilation of garnet elasticity data to examine composition-elasticity systematics of garnets. Our results suggest that pyralspite and ugrandite have different relationships between bulk sound velocity (V ϕ ) and mean atomic weight (M 0 ), between Poisson’s ratio (σ) and density (ρ), and between G / K s and K s /ρ ratios. A large error may occur when the systematics are applied across different garnet groups.