Early Precambrian within-plate basalts from the Kaapvaal Craton in southern Africa: a case for crustally contaminated komatiites

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-undepeleted komatiite in the mid- to upper crust with Archean granitoids as the major contaminants. Widespread 2.3 Ga old within-plate, anorogenic granites in the Kaapvaal Craton may be crustal melts produced by komatiitic magmas heating the crust. -from Authors