komatiita

Komatiite is a rare, ultramafic volcanic rock characterized by very high magnesium content and relatively low silica, typically formed from basaltic magma that crystallized rapidly at or near the surface. The name derives from the Komati River in present-day KwaZulu-Natal, South Africa, where early examples were described. Komatiites are notable for their high MgO content and for textures produced by rapid cooling of hot, buoyant magmas.

A distinguishing feature of komatiites is their spinifex texture, consisting of elongated, needle-like olivine and pyroxene crystals that form during rapid crystallization of a magnesium-rich melt. They commonly occur as lava flows, with accompanying sills and pillow lavas within greenstone belts, and may display cumulate textures in some sections. Their chemical signature places them at the ultramafic to highly Mg-rich end of volcanic rocks, with relatively low silica compared with many basalts.

Geologically, komatiites are largely Archean in age, reflecting hotter mantle temperatures in Earth's early history. Most are dated roughly between 3.5 and 2.5 billion years ago, with some younger occurrences in the Proterozoic. They are thought to form by high degrees of partial melting of mantle peridotite, producing low-viscosity, Mg-rich melts capable of erupting to form flowing lavas.

Economically, komatiites are important as potential hosts for nickel-copper sulfide mineralization, driven by sulfide saturation and immiscible metal-rich phases generated during extrusion and flow. They are commonly associated with Ni-Cu-PGE sulfide deposits in ancient greenstone belts.

Distribution-wise, komatiites occur in Archean shield areas worldwide, most notably in the Barberton Greenstone Belt of South Africa and in parts of the Canadian Shield, with occurrences also reported in other ancient terranes.