Ndlopfu is located above some of South Africa’s, and the World’s, oldest rocks. If you strip away all the soils you will sit on rocks that form part of the Kaapvaal Province, a geological province formed around 3.5 billion years ago of the earth’s 4.8 billion year age (the Early Archean period)
Nonpalinspastic map showing Late Archean and Early Proterozoic supracrustal development from 2900 Ma to 1800 Ma.
The original geological rock components of the Kaapvaal Province were granites. These are primary igneous rock formed from the slow cooling of the earth’s magma (molten core) as it rises towards the surface. It is fascinating to keep in mind that all this happened long before the formation of the earth’s continents which only happened around 500 million years ago. (The Godwana Era).
This “old” age is important because, subsequent to those early formative years, a lot of geological structural activity has taken place, at least five major “D” events*. The two most notable were the formation of the Pongola Supergroup which is said to have been a failed continental rift process, and then, the actual rifting process that led to the breakup of the continents, known as The Godwana Era. Therefore, in combination with these significant “D” events and during the 3 odd billion year lifespan of the Kaapvaal granites, these igneous Kaapvaal rock outcrops that you will see at Ndlopfu and the surrounding “koppies”, will show incredible stresses and strain characteristics, involving both physical force as well as heat. It is therefore almost impossible to define the intrinsic igneous rocks into any one type. It is safe to say that they are all “granatoid gneisses” (a reheated and subsequently cooled form of igneous rock).
These old rocks have also subsequently gone through an enormous period of weathering and erosion which has led to the thick “course sandy” layer that is so prevalent in our flat surroundings, in our river beds and the soft soils of the land. Our river bed soils are also characteristically quartz rich, in particular the load leading up to the trig beacon outlook point. This is a dominant, weather resistant ingredient from the granites originally formed 3 billion years ago!
Accompanied to any such catastrophic forms of magmatic, volcanic and rifting forces there will be innumerable feeding fissures of various sizes and shapes that feed the liquid molten material upwards and outwards, not like volcanoes, but like blood vessels or ground water cracks (geologically, they are known as leucocratic feeder veins). These fissures were also a means for liquids to escape from high stress and heat zones. Only the lightest and least viscous of liquids (almost pure silica that makes up quartz) would have flowed through these cracks in the rocks, so when the cataclysmic events eventually calmed down they would then have crystallized during the cooling down period to form these resistant “white cracks” that we see through our various outcrops.
The “Wit Klippe” outcrop is a good example where there was a particularly large “boudinage” (stretching of a vein to form thin and thicker parts) of such a slica/quartz rich vein during one of the “D” deformation phases. A relatively quick cooling period would have caused the glassy nature of the “Wit Klippe” (after all glass is a silica/quartz mixture that has been cooled down very quickly).
The above is a simple summary of the Geological formations found on Ndlopfu to assist our members in understanding these formations of our area. It is not a scientific paper. I am therefore always open to any comments, corrections or questions.
Maurits Huizinga (PhD Geology – UKZN Durban) (Unit #44)
Special thanks to Maurits Huizinga for the use of this article.
Bibliography: Tankard, A.J. et.al., 1982. et. al. Crustal Evolution of Southern Africa, pp 23-89
*”D” event – a major geological structural event that had a significant impact on the geology of an area/region. E.g. the breakup of Gondwana land would be one such “D” event, also the folding of rock strata as per those sandstone folds seen when coming through the Strydom tunnel.