Critical Phenomena and Garnetization of Hydrous Eclogite at P = 3.7–4.0 GPa and T = 1000–1300°C

Abstract

The phase relations upon eclogitization of basalt and melting of H2O-bearing eclogite were studied experimentally for basalt–H2O in the range of P = 3.7–4.0 GPa and Т = 1000–1300°C. It is shown that the phase relations depend on temperature. The formation of a supercritical fluid/melt occurs at T = 1000°C and P = 3.7 GPa; the eclogite‒garnetite transition, at T = 1000–1100°C and P = 3.9 GPa; and partial melting of eclogite with the formation of a Na-alkaline silicate melt and clinopyroxenite restite, at 1150 and 1300°C. the supercritical fluid/melt has a high reactivity, which results in the formation of garnet megacrysts, enrichment of garnet in Ti, and replacement with clinopyroxene, the formation of ilmenite, K-bearing amphibole, and the transformation of eclogite into garnetite due to the mass crystallization of garnet.