Petrological discrimination among Precambrian dyke swarms: eastern Kaapvaal craton (South Africa)

Summary, in English

Age-determinations on a complex array of mafic dykes across the eastern Kaapvaal craton (Olsson et al.. 2010) are complemented herein by field evidence, dyke trend analysis, and petrological characterization of 58 dyke samples. similar to 2.95 Ga SE-trending, a similar to 2.65 Ga E- to SE-radiating, and similar to 1.90 Ga NE-trending swarms can be distinguished. Prominent Archean (similar to 2.95 and similar to 2.65 Ga) dyke ridges contain basement xenoliths, and have a more quartz-oversaturated, andesitic and calc-alkaline character. Proterozoic (similar to 1.90 Ga) dykes are, on the other hand, more aeromagnetically prominent tholeiitic basalts with higher modal (Fe, Ti)-oxide contents. Multi-elemental statistics indicate that the best geochemical discrimination is found between Archean high-Sr/V and La/Yb and Proterozoic low-Sr/V and La/Yb dyke swarms. The calc-alkaline character of Archean dyke swarms is augmented by LILE-enriched spider-element patterns with steeper REE-slopes as compared to the Proterozoic swarm. Geochemical similarities are roughly consistent with the similar to 2.95 and similar to 2.65 Ga dykes having fed coeval lavas within the Nsuze Group and Allanridge Formation (upper Ventersdorp Supergroup), respectively. similar to 1.90 Ga dykes match coeval sills on both the Zimbabwe and Kaapvaal cratons, and are presumed feeders to Soutpansberg Group lavas. This new information provided by dated feeder dyke swarms leads to a re-evaluation of petrotectonic settings, ranging from continental back-arc to radiating swarms emanating from igneous (plume?) centers.