charnockites

Charnockite is a coarse-grained granulite facies metamorphic rock that is typically felsic to intermediate in composition. It is characterized by the presence of orthopyroxene together with clinopyroxene, plagioclase, and quartz, often with alkali feldspar in smaller amounts. The mineral assemblage gives a hard, dense rock with a granular texture. Accessory minerals may include garnet, magnetite, ilmenite, zircon, and rutile.

Formation and metamorphism: Charnockites form during high-temperature, high-grade metamorphism, usually at crustal depths corresponding to granulite facies (temperatures roughly 700–900°C and pressures of several kilobars). They commonly represent granitoid protoliths that underwent granulite facies metamorphism, and in many cases show evidence of partial melting (anatexis) producing leucosomes and felsic melts.

Occurrence: They are widespread in ancient crustal blocks (Precambrian shields) and granulite belts, notably in parts of the Indian shield (South Indian granulite terrain), Africa, Greenland, and Australia.

Relation to related rocks: The term charnockite is often used for orthopyroxene-bearing granulites, and closely related rocks known as enderbites are garnet-rich granulites that share similar origins. These rocks collectively illustrate high-grade metamorphism of granitic to pelitic precursors in ancient continental crust.