ABSTRACT

The Belingwe Belt contains an andesitic suite, two suites of komatiites associated with voluminous tholeiites, and assorted intrusive igneous rocks. Some of the latter include remarkably fresh komatiite and basalt, containing little altered olivine and clinopyroxene phenocrysts and optically fresh glass. However most rocks are altered, probably both by early hydrothermal and later regional metamorphism, as well as by recent weathering. Within the very fresh flows in the Reliance Formation SiO2, TiO2, Al2O3, FeO, MgO, Na2O, NiO, Cr2O3, Zr, Y, REE and platinum group elements vary in a manner consistent with models which involve fractionation of olivine of the observed compositions and consistent with experimentally determined partition coefficients. These elements were probably nearly immobile during alteration.

The Bend and Reliance komatiite suites are compositionally distinct in incompatible trace element ratios (e.g. Zr/Ti, Y/Ti). Crustal contamination of komatiite lavas is probably less than 1 % by mass. The lowermost volcanic unit, the Hokonui Formation is, in contrast, a typical calc-alkaline sequence.