Geology of South Africa

South Africa is the country at the southernmost corner of Africa. Cape Town, the capital, is named after the Cape, the southernmost point of the African continent.

This country has numerous famous geological features, which are rather easy to visit, because of the dry climate with no or little vegetation hiding the geology. Except for a small humid stripe along the southeastern coast, the center of the country is a semi arid plateau surrounded by mountain ridges.

The main geological feature is of rather ancient, Precambrian origin, about 3 Ga old. The central areas are composed of Precambrian crystalline rocks, mainly gneis and granite, but also Archean mafic-ultramafic volcanic sequences. Those rocks are among the oldest known rocks on Earth. There exist a few locations with much older rocks, e.g. in iceland, but they are heavily alterated and found only in very small spots. So the Precambrian rocks of South Africa are the oldest formation of rocks with a considerable size. Probably the most interesting fact among those rocks are structures created by the fast cooling of the lava which require much different atmospheric conditions to be formed. They allow the reconstruction of the composition of the atmosphere while they were formed and thus allow a glimpse on Earth's atmosphere 3Ga ago.

Many deposits originate from this era, gold bearing conglomerates and banded iron formations. The gold is of great economic value and backbone of the Kruger Rand curreny, symbolized by the famous gold coins. And there are numerous extraordinary impact envents (aka meteors) which happend about the same time.

Later millenia saw volcanism, especially the formation of the famous diamond bearing kimberlite pipes about 1Ga ago. Kimberlite is formed under high pressure and temperature in the pipes deep inside the volcano, and during this process the carbon in the lava is converted into diamond. And diamonds are the second important backbone of South Africa's economy. While there are other important diamond deposits on earth, e.g. in Russia and Australia, the center of all diamond deposits is still in the southern end of Africa. Beneath South Africa Namibia also has important diamond and kimberlite deposits. Even the diamonds in Brazil in South America originate from here. Brazil does not have Kimberlite pipes, the diamonds were removed by erosion from the

The most important and easily visible volcanic era happened about 200Ma ago, when the supercontinent Pangaea broke into pieces. Huge graben systems formed, where the continental crust became cracks several thousand kilometers long. Those structures/events are always connected with volcanism and earth quakes. Cracks opening at this graben produced enormous layers of the so called Trapp basalt. Repeated eruptions produced layer above layer of lava flows. If you remember the volcanic eruption in the Disney animation movie about the dinosaurs, this is the time and the place! But be aware: Disney is not famous for the scientific accuracy of the films....

The country has numerous limestone and dolomite areas suitable for karst development The total area of karst is very small in relation to the size of the country. The main karst areas are Bredasdorp in the south, Groot Swartberge, a little to the north, a huge area south of Kuruman, and in Transvaal and Drakensberg. Most of the carbonate rocks are dolomites, often criss-crossed by igneous dykes. The premier show cave is Cango Cave which is located in the Swartberge. This are is probably the best explored karst of the country with the longest known caves. More show caves of decent size are located in Transvaal and Drakensberg around Johannesburg. This major cave area has seven of the ten longest caves of the country. Especially the Wonderfontein valley shows numerous karst features, like poljes and gigantic sinkholes. Some of the collapses are man made, as the gold mines below the karst changed the drainage.

The country also has notable non carbonate karst. There are several caves in the hard sandstones of the Cape Peninsula. At the southern end of the Drakensberg area are caves and karst features formed in quartzite. However, those caves are not of touristic interest.