Granitoid-greenstone relationships in the eastern Kaapvaal craton and implications for early crustal evolution

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Following up on our project, where the early Archaean continental crustal histories of the Ancient Gneiss Complex (AGC),of Swaziland and the Itsaq Gneiss Complex (IGC) of southern West Greenland) have been studied, we now focus on the geochemistry of mafic and ultramafic rocks of the lowermost stratigraphic units of the Barberton Greenstone Belt, the ca. 3.53 Ga Theespruit and Sandspruit Formations, South Africa, as well as on greenstone inliers in the Ancient Gneiss Complex of Swaziland. The preliminary results of our first project phase hint at a felsic basement to the above greenstone sequences and older continental crust as now exposed in the AGC. Chemical signatures of mafic-ultramafic volcanic rocks possible crustal contamination may be traced using a combination of major and trace elements and Hafnium-Neodymium isotope compositions. Moreover, we plan to carry out 142Nd analyses on different rock types (gneisses, amphibolites) of the Ancient Gneiss Complex and the lithologies of the Barberton Greenstone Belt to investigate whether the oldest rocks of the Kaapvaal craton had an early differentiation history that possibly began in the Hadean, when the extinct nuclide system was still active. We shall investigate whether a possible 142Nd anomaly may have been diminished by juvenile crustal contributions with time or whether it sustained in younger magmatic rocks.