granitoides

Granitoids, also called granitoid rocks, is a broad term in geology for coarse-grained intrusive rocks with granitic composition. They are dominated by quartz and alkali feldspar (potassium feldspar), with plagioclase and minor mafic minerals such as biotite, hornblende, or muscovite. The texture is typically phaneritic, and some granitoids are porphyritic with large mineral grains.

They include granite, granodiorite, tonalite and related rock types; the term emphasizes chemical composition rather than a strict IUGS category. They are distinguished from more mafic plutonic rocks by high silica and relatively low contents of magnesium and iron.

Formation: Granitoids crystallize from silica-rich magmas produced by partial melting of crustal rocks or by differentiation of mantle-derived magmas. They commonly form in continental crust, especially at convergent plate margins, in post-collisional extensional zones, and as large batholiths that crystallize at various depths. Petrogenesis often involves fractional crystallization, crustal assimilation, and magma mixing; source materials can be granitic or granodioritic in character.

Significance: Granitoids constitute a major component of continental crust and are important for understanding crust formation and tectonics. They host various mineral deposits and occur in many tectonic settings worldwide, including the Cordilleran and Variscan belts, and the Australian Shield.