Abstract
Archean and Early Proterozoic basalts from the Kaapvaal Craton in southern Africa have geochemical characteristics of subduction-related basalts. These basalts, however, cannot be produced in the subcontinental lithosphere, if ultramafic xenoliths depleted in Fe, Ti, and Ca are representative of this lithosphere. Geochemical and isotopic data are consistent with an origin by assimilation-fractional crystallization of Al-undepleted komatiite in the mid-to upper crust with Archean granitoids as the major contaminants. The proportion of granite to tonalite needed in the contaminant is higher for most of the Proterozoic basalts than it is for the Archean basalts. Widespread 2.3 Ga old within-plate, anorogenic granites in the Kaapvaal Craton may be crustal melts produced by komatiitic magmas heating the crust. Komatiitic magmatism in southern Africa could have lasted for (), and many Archean and Early Proterozoic within-plate basalts from other regions also may be crustally contaminated komatiites.
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