Reference work entry
Archean volcanic rock, mantle temperature
Komatiite is a volcanic rock of ultramafic composition. It is distinguished from the more common basaltic magma by a higher content of MgO (>18%) and low contents of most other elements.
Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Examples are now known in most Archean greenstone belts, and komatiitic basalt, the fractionation product of komatiite, occurs in Proterozoic belts of northern Canada. The komatiites of Gorgona Island off the coast of Colombia are the sole well-documented example of Phanerozoic komatiite. The older, 3.5 Ga komatiites have different chemical compositions from younger komatiites, being characterized by high CaO/Al 2O 3 and low Al 2O 3/TiO 2. Important ore deposits of Ni-Cu sulfides are found in...
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