The paragenesis of garnet in charnockite, enderbite, and related granulites

Abstract

SummaryThe presence of garnet in acid rocks of the charnockite series south of Madras is reported. Petrographic deseriptions of garnetiferous enderbites and related pyroxene-granulites, khondalites, and leptynites are accompanied by new chemical analyses of 6 rocks, 8 garnets, and 5 orthopyroxenes from the type area near Madras, and from Ceylon, Varberg, and Uganda. The garnets show a considerably higher FeO/MgO ratio than the coexisting ortbopyroxenes and the host rocks. The presence or absence of garnet appears to be related to the bulk chemistry of the rocks. Basic garnetiferous granulites associated with these rocks are considered to represent an unstable mineral assemblage and may be genetically unrelated to the acid types. Attention is drawn to the prevalence of enderbitic rocks in the type area.