Mineralogy and metamorphic conditions of a garnetiferous lens from the eastern Chalkidiki peninsula, northern Greece

Abstract

A small lensoidal garnetiferous body, consisting of garnet + amphibole + epidote + quartz, and occuring within the gneisses, amphibolites and migmatites of the eastern part of the Chalkidiki main body, is studied in terms of petrography, mineralogy and metamorphic conditions. Garnet corresponds to almandine rich almandine-grossular solid solution and displays negligible core-rim compositional variations. Garnet grains exhibit alteration to amphibole (mainly ferropargasitic hornblende and ferropargasite) and epidote. The chemical composition of garnet and amphibole imply conditions of upper amphibolite facies. It is considered that the studied garnetiferous lens may represent a retroeclogite, lacking any relic eclogitic assemblage, which completely recrystallized and equilibrated extensively under the prevalent high-T amphibolite facies. The slight enrichment of epidote in Ce, La, Y, and consequent zoning are attributed to compositional variations of the fluid phase during the amphibolitization stage.