Southern Region

One of the dykes located close to the centre of the impact, at DaskopThe boulder in the dyke shows the small, fractured inclusions of unmelted rockThese rocks have also been the target of graffiti artists - in this case San hunters perhaps 2000 years ago. Shown here is an engraved hippopotamus.An engraving of a rhinocerosThe stone walls of the villageNASA Lunar Orbiter image

MORE ABOUT THE VREDEFORT DOME

From a high altitude the partial ring of hills in the Vredefort Dome bear a strong resemblance to the larger, near-circular ring of hills to the north and south of Vredefort. These are the Magaliesberg hills, on the northern side of this ring, cutting through Pretoria, and the the Witwatersrand ridge, on the southern side of this ring, cutting through Johannesburg. The Witwatersrand ridge, surrounding this uplifted area, is known as the "Johannesburg Dome".

The gold mine dumps of Carletonville can be seen west of Johannesburg and due north of Vredefort. The gold mines of Klerksdorp and Welkom lie north west and south west of Vredefort, and their dumps are also easily seen, forming a half ring of gold mines around Vredefort.

The Magaliesberg - Witwatersrand feature is the result of natural upliftment of sedimentary sandstone layers, what was once the bottom of a sea.

The Magaliesberg rock layers slope down to the north, while the Witwatersrand rock layers slope down to the south. The "Johannesburg Dome" in the center this feature is occupied by the Achaean granitic crust, some 3000 to 3400 million years old.

The same rock layers seen in the Witwatersrand are found in the Vredefort dome hills, but here they are found standing nearly vertically - the result of extreme upliftment.

The Vredefort structure is currently regarded the biggest and oldest clearly visible impact structure on Earth. It just beats the Sudbury impact structure in Canada for this ranking. The Sudbury structure is some 200 km in diameter and is estimated to be 1850 million years old.

Evidence of four impacts even older than than Vredefort, that occurred 3200 to 3500 million years ago, has been found in the greenstone rocks around Barberton in Mpumalanga, South Africa, and corresponding rocks in the eastern Pilbara block of Western Australia. However, these impacts are no longer recognizable as structures on the surface like those in the Vredefort area. For more information refer to
http://www.hartrao.ac.za/other/vredefort/vredefort.html

Acknowledgement:

The photographs shown here were taken on a very informative tour of the area led by Roger Gibson and Uwe Reimold. They are with the Department of Geology at the University of the Witwatersrand. For serious enquiries, these are experts.

Dr. Roger Gibson, email: 065rlg@cosmos.wits.ac.za
Prof. Uwe Reimold, email: 065wur@cosmos.wits.ac.za
Prof. Morris Viljoen, email: 065mjvil@cosmos.wits.ac.za

For the serious geologist, 1:50 000 scale geological maps of the area are available from the South African Council for Geosciences, together with an explanatory booklet "The Geology of the Vredefort Dome", written by A.A. Bisschof, ISBN 1-875061-60-6, published 1999 by the Council.