Komatiites are igneous rocks mainly of Archaean age. Their ultramafic origin is controversial and has been attributed to either high degrees of dry melting of peridotite in deep mantle plumes at temperatures up to 500°C hotter than today, or to melting at shallow depth, in volatile-rich (hydrous) mantle with temperatures not much different than the 1200–1500°C (for basalts and boninites) in contemporary mantle of subduction zones or below Archaean oceanic ridges. Komatiites often have exquisite disequilibrium mineral textures seldom seen in younger rocks. These spinifex textures give komatiite a mystical aura, keenly sought after, because a detailed understanding of their...

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