TEMPERATURE VARIATION OF ELASTIC CONSTANTS OF PYROPE-ALMANDINE GARNETS

Abstract

Elastic constants of three natural pyrope-almandine garnets (Fe/(Mg+Fe)=0.18, 0.48 and 0.58) were measured by an RPR method in the temperature range between -190° and 80°C. The temperature derivative of bulk modulus ∂K_s/∂T does not depend much on the composition, but those of shear constants ∂C₄₄/∂T and∂C_s/∂T [C_s=(C₁₁-C₁₂)/2] increase considerably with increase in the Fe-content. The temperature derivatives of the elastic constants (kbar/deg) of pyrope and almandine at room temperature are determined by extrapolation:
From the measured elastic parameters of garnet, the material of the high velocity layer (V_p=8.6km/s and V_s=4.9km/s) in the oceanic lithosphere is interpreted as eclogite or garnet peridotite constituted dominantly of garnet.