Petrological discrimination among Precambrian dyke swarms: Eastern Kaapvaal craton (South Africa)
Date
2010
Authors
Klausen M.B.
Soderlund U.
Olsson J.R.
Ernst R.E.
Armoogam M.
Mkhize S.W.
Petzer G.
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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. © 2010.
Description
Keywords
age determination, Archean, dike swarm, igneous geochemistry, petrology, Precambrian, tectonic setting, tholeiitic basalt, xenolith, Kaapvaal Craton, Zimbabwe Craton, Araneae
Citation
Precambrian Research
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