U-Pb geochronology of the Tsineng dyke swarm and paleomagnetism of the Hartley Basalt Formation, South Africa : evidence for two separate magmatic events at 1.93 – 1.92 and 1.88 – 1.84 Ga in the Kalahari craton

Sammanfattning: Robust geochronology and well-constrained paleopoles are the main tools for paleogeographic reconstructions. Through the completion of so called barcode diagrams (matching of coeval events of mafic magmatism between blocks) and determination of the apparent polar wander paths, these studies provide a better understanding of the position of continents and supercontinents in the past. The robust U–Pb baddeleyite age of 1922 ± 6 Ma for the RP353 dyke of the Tsineng Swarm in the western Kaapvaal Craton, obtained in this study, establishes a link between the Tsineng Dyke Swarm and the 1928 ± 4 Ma Hartley Basalt Formation, as well as ca. 1927 Ma dolerite sills intruding the Waterberg Group (Moshaneng dolerites). The comparison of barcode diagrams for the Kaapvaal and Zimbabwe cratons can constrain the timing of the collision between the two cratons to ca. 1.92 to ca. 1.88 Ga, though future studies are required to confirm this inference. Paleomagnetic data for 77 drill core samples from the Hartley Basalt Formation of the Olifantshoek Supergroup in western Kaapvaal Craton, provides a paleomagnetic pole (N°= 22.7, E°=328.6, α95=11.7) for the primary remanence direction. The new robust paleopole for the Hartley Basalt Formation fits well with in the existing Paleoproterozoic polar wander path of the Kaapvaal craton. Geochronology, paleomagnetism and geochemistry of the 1.93 – 1.92 Ga and 1.88 – 1.84 Ga rocks in the Kaapvaal Craton points towards two separate magmatic events.