Charnockites of the type area near Madras; a reinterpretation

Abstract

Charnockite is redefined as a hypersthene-quartz-feldspar rock, with or without garnet, characterized by greenish blue feldspars, with microperthite dominant. The charnockite suite consists of a group of genetically related alaskites, charnockites (birkremites), enderbites, and hypersthene-quartz syenites, emplaced as thick sheets and lenses in gently folded basement rocks and subsequently subjected to metamorphic reconstitution and recrystallization accompanied by unmixing of perthites, formation of garnet, and other mineralogic changes. Various rock types which have been assigned to the acid, basic, and intermediate divisions of the so-called charnockite series are described. Only those of the acid division are considered charnockites; others are either genetically unrelated or hybrid rocks.