Petrological discrimination among Precambrian dyke swarms: Eastern Kaapvaal craton (South Africa) |
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| Authors: | MB Klausen U Söderlund JR Olsson RE Ernst M Armoogam SW Mkhize G Petzer |
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| Institution: | 1. Department of Earth Sciences, University of Stellenbosch, Matieland 7602, South Africa;2. Department of Geology, GeoBiosphere Science Centre, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden;3. Ernst Geosciences, 43 Margrave Ave., Ottawa, Canada K1T 3Y2;4. School of Geological Sciences, University of KwaZulu-Natal, Durban 4000, South Africa |
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| Abstract: | 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. ∼2.95 Ga SE-trending, a ∼2.65 Ga E- to SE-radiating, and ∼1.90 Ga NE-trending swarms can be distinguished. Prominent Archean (∼2.95 and ∼2.65 Ga) dyke ridges contain basement xenoliths, and have a more quartz-oversaturated, andesitic and calc-alkaline character. Proterozoic (∼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 ∼2.95 and ∼2.65 Ga dykes having fed coeval lavas within the Nsuze Group and Allanridge Formation (upper Ventersdorp Supergroup), respectively. ∼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. |
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| Keywords: | Archean Paleoproterozoic Kaapvaal craton Dyke swarms Petrology Geochemistry |
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