a day ago
Fascination of the Dome's geological wonder explored
Whether it is scientific, curiosity, historical, or cultural interest, ecotourism, or adventure activities, the Vredefort Dome has something special to offer each visitor. The site's importance and value in promoting desired tourism activities and contributing to the research by geological scientists from all over the world, cannot be overlooked.
Although not proclaimed as a World Heritage Site in terms of South African law yet, it has been inscribed on the Unesco World Heritage List since 2005, being the oldest, largest and most deeply eroded complex meteorite impact structure in the world – nearly twice as big as the impact that killed the dinosaurs 65 million years ago.
Yet many tourists do not know what to expect when visiting the Vredefort Dome World Heritage Site, says Prof. Rodger Gibson from Wits University's School of Geological Sciences. Having spent many years researching the Vredefort Impact and as co-writer of the book Meteorite Impact, he found that people often mistakenly think they will be able to see the impact as a hole in the ground. Yet the uniqueness of the Vredefort Dome World Heritage Site lies in the geological wonder.
Eager to learn and explore these geological wonders, 37 participants from the Gauteng, Free State, and Northwest provinces joined an excursion in the Vredefort Dome on Saturday, led by Gibson and organised by the Dome Conservancy.
The geological uniqueness seen here in the Dome is a result of rivers that, over many hundreds of millions of years, eroded the sides of the crater and most of the cooled melt-rock. This exposed the rocks that once lay underneath the crater. Today, the rocks in the Vredefort Dome are exposed in several rings. The oldest rocks that were buried deep within the crust before the impact event are found in the centre.
These are mostly granite gneisses over 3 000 million years old. Parys and Vredefort are built on these gneisses that have been mined for their stone in many quarries. The hills of the Vredefort mountain range are made of hard white quartzite rock, with the valleys in between made of softer shale. Some thin layers containing a little gold were once mined from these rocks near Venterskroon.
Beyond the hills towards Potchefstroom and Fochville lie softer lava and dolomite rocks that form flatter land. All these rocks form part of the Vredefort Dome. Only a small part of the Vredefort Dome along the Vaal River, between Parys/ Potchefstroom and Vredefort/ Potchefstroom roads, has been declared a World Heritage Site.
Gibson, on Saturday, first gave an introduction to the South African geology and the Vredefort Dome impact at the Salvamento granite quarry at Kopjeskraal. At the granite quarry, one can see extraordinary examples of Pseudotachylite, which is a glassy or fine-grained rock formation from brecciation followed by the melting of granite. Broken up granite blocks could be seen in between these Pseudotachylite breccias.
At Schurwedraai, the uniqueness of the rock formations in the Dome and the various unique mineral compositions in the rocks were explained. Gibson also explained the impact of the ice age and glaciers' movements on the Dome landscape about 300 million years ago.
Evidence of shock is an important feature of a meteorite impact event, and this evidence was shown in the shatter cones that could be seen in the Booysens shale at Rooderand. Shatter cones are cone-like, or striated fractures in rocks, that were formed due to the extreme shock wave that went through the rock formations during the time of the impact. These shatter cones can be seen throughout the first impact ring, also known as the Vredefort Dome Mountain Land.
The last point of interest visited was the Vredefort Granophyre Dyke at Daskop. Granophyre is an impact melt rock composed of irregular intergrowths of quartz and feldspar minerals and was formed during the impact. This Granophyre Dyke is an important archaeological site dating back to the first Bushmen who were hunting here. According to archaeologists, this was a rain-making site, as can be illustrated through the series of petroglyphs, or rock engravings. Some of these petroglyphs are over 6000 years old.
The excursion gave a fascinating perspective on the geology of the Dome days before the GeoCongress in Bloemfontein.
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