ULTRAMAFIC ROCKS IN THE CENTER OF THE VREDEFORT STRUCTURE (SOUTH-AFRICA) - GEOCHEMICAL AFFINITY TO BUSHVELD ROCKS

The geochemistry and mineral chemistry of ultramafic rocks in the cent re of the Vredefort structure have been reinterpreted. A detailed exam ination of previously published major element, trace and REE analyses as well as mineral analyses strongly suggests a magmatic origin in con trast to a previously postulated tectonic emplacement of mantle materi al. A strong geochemical affinity to ultramafic rocks from the Bushvel d Complex is evident. The magmatic nature of the ultramafic rocks in t he centre of the Vredefort structure has implications for the discussi on of the metamorphic history of the Vredefort structure which shows e vidence of unusually high, and as yet not satisfactorily explained, ge othermal gradients during peak metamorphism. (C) 1997 Elsevier Science B.V.