Faculty of Natural and Agricultural Sciences
School of Physical Sciences
Department of Geology
Selected Highlights from Research Findings
The Limpopo Mobile Belt, which lies across the border between Zimbabwe and South Africa and extends westwards into Botswana, is one of Earth's most ancient high-grade orogenic belts and has been the subject of controversy for decades, particularly with regard to its age. This belt is one of the most fundamental crystal structures in southern Africa and reflects the suture between the Kaapvaal craton of South Africa in the south and the Zimbabwe craton in the north. The central part of this large, complex suture zone is constituted by the so-called Central Zone, an apparently exotic small crustal plate that was emplaced through early plate tectonic processes on Earth. Conventional dating and metamorphic petrological techniques applied over decades have failed to resolve the age controversy, that is, whether the Limpopo Belt reflects two major orogenic events, at c. 2.7 and 2.0 Ga, or only one at about 2.0 Ga. Recent and ongoing research on this problem, led by Dr Martin Rigby, is applying the most up-to-date techniques of the pseudosection approach to thermobarometry through the use of Thermocalc software. The results have clearly indicated that there was only one major collision and suture, at about 2.0 Ga between the Zimbabwe craton and an already co-joined Central Zone-Kaapvaal assembly, probably of c. 2.7 Ga vintage. This reflects an important step forward in the understanding of one of Earth's oldest and most enigmatic mobile belts, which also forms one of the really fundamental crustal features related to most major subsequent geological events in southern Africa and its very large mineral deposits
Contact person: Dr M Rigby.
South Africa probably has the best Precambrian rock record of any comparable terrain on Earth. Among this record is a superb succession of sedimentary basins from the c. 3.1 to 2.7 Ga Witwatersrand gold-bearing depository (the oldest large basin preserved on Earth), to the c. 2.7 Ga Ventersdorp basin, the c. 2.67 to 2.1 Ga Transvaal Basin, and the c. 2.0 to 1.8 Ga Waterberg basins. Mainstream science supports a viewpoint whereby change in the chemical composition of the hydrosphere-atmosphere system on the planet, from an early reducing environment to one that gradually became more oxygenating, was marked by what is often termed the ‘great oxidation event’ at some time between about 2.3 and 2.0 Ga. A detailed study of the nature of the very large braided channel systems that are preserved in the Waterberg basins by Dr Adam Bumby and PhD student Markus van der Neut suggested a possibly unique fluvial style at that time. Expansion of these studies into the Transvaal basin by Prof Pat Eriksson confirmed the idea that Palaeoproterozoic fluvial styles were somewhat unique, characterised by palaeo-gradients that resemble no modern river systems. Modelling of the concomitant palaeo-atmospheric conditions in cooperation with Prof Hannes Rautenbach, head of the Department of Geography, Geoinformatics and Meteorology, suggests that a reducing greenhouse atmospheric setting must have continued for much longer than originally thought, and has placed a question mark on the universal nature of the so-called ‘great oxidation event’, at least for the Kaapvaal craton of South Africa
Contact person: Prof PG Eriksson.
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