Petrogenesis of Syenites and Granites of the Schiel Alkaline Complex, Northern Transvaal, South Africa

The Schiel Complex (2059 +35/-36 Ma) is one of the alkaline intrusive suites emplaced in the northern part of the Kaapvaal craton during the Early Proterozoic. It is a typical mixed silica-undersaturated to -oversaturated complex bearing a wide composition of rocks, including pyroxenite, glimmerite, foskorite, carbonatite, dolerite, shonkinite, and dominant syenite and granite. The mineralogical and geochemical features of the syenites and granites define a petrologic association with quartz + alkali feldspar + diopside-hedenbergite clinopyroxene + lepidomelane biotite ± ferro-edenite to ferro-pargasite hornblende as major mineral phases; accessories are apatite, titanite, zircon, and magnetite. Chemically, they are alkaline to peralkaline and characterized by relatively low contents of Al, Mg, and Ca and high contents of high field strength elements, including Nb, Ga, Y, and rare earth elements. These features are characteristic of most A-type granitoids. The genesis of syenites and granites of the Schie...