A palaeomagnetic test of the Kaapvaal-Pilbara (Vaalbara) connection at 2.78 Ga

Integrated U-Pb geochronology and palaeomagnetic study of mafic to felsic v olcanic rocks of the Derdepoort Belt of South Africa are employed to test t he hypothesis that the Pilbara and Kaapvaal Cratons were joined as part of a Late Archaean 'Vaalbara' supercontinent. An age of 2782 +/- 5 Ma is deduc ed for eruption of the Derdepoort basalts, bracketed by a concordant SHRIMP zircon age of 2781 +/- 5 Ma for overlying felsic volcanics and a concordan t isotope dilution zircon age of 2783 +/- 2 Ma for underlying granite of th e Gabarone Complex. Based on the low (subgreenschist) metamorphic grade of the basalts, the presence of highly stable single domain magnetite, and a p ositive conglomerate test, the magnetization of the Derdepoort basalts is i nferred to date from the time of their emplacement and cooling at 2782 Ma. Results yield a primary palaeopole at 005 degrees E, 40 degrees S (A(95) = 18 degrees), and indicate a palaeolatitude of 64.5 +/- 17.5 degrees for the Kaapvaal Craton at 2782 Ma. Published palaeomagnetic data for the Mount Ro e Basalts of the Pilbara Craton indicate a palaeolatitude of 34.3 +/- 6.4 d egrees at 2772 +/- 2 Ma. The latitudinal separation of 30 degrees implies t hat the cratons were not contiguous at 2.77 to 2.78 Ga, although the possib ilities that the cratons could have been joined during other intervals of r i me, or that they were non-contiguous parts of a larger continent, are not ruled out.