Pb-isotope geochronology of the Schiel complex, Northern Transvaal, South Africa

Abstract

New Pb-isotopic data from various lithological units of the Schiel Alkaline Complex, northern Transvaal, South Africa, indicate an age of 2059 + 35 − 36 Ma for this intrusion. As such the Schiel Complex represents another manifestation of the widespread magmatism that affected the Kaapvaal Craton at this time and which also includes, among others, the Bushveld Complex and the Phalaborwa Complex. The new data additionally show that alkali granite, formerly grouped with the complex, should rather be interpreted as country rocks that were metasomatised during the emplacement of the Schiel Complex. Age determinations have also been made of pyroxenite occurring within the Schiel Complex and of migmatite of the Bandelierkop Formation adjoining the complex to its southwest. The results provide indistinguishable dates close to 3.2 Ga for both the pyroxenite and the migmatite and confirm the interpretation of the pyroxenite as a xenolith of Bandelierkop Formation incorporated in the Schiel Complex. The high μ-values of the pyroxenite and migmatite dates furthermore suggest that the ca. 3.2. Ga date represents metamorphism (serpentinisation and migmatisation respectively) of these lithologies and that the Bandelierkop Formation has a pre-history before 3.2 Ga.