As a result of the extreme impact and the resulting upheaval, the Dome has been left with many unique geological features
The Earth heaved and melted….
Clearly visible at a quarry at Leeuwkop near Parys , one of the indicators of the impact is revealed. In the cut surface of the rock the pale and medium grey colours of granite can be seen, But more obvious is the wide dark grey band in the centre, containing large and small fragments of granite. This is “pseudotachylite brecchia” – the dark grey granite that was melted by impact and flowed, carrying chunks of un-melted granite within the melt.
….And flowed and solidified
The force of the impact produced deep fractures in the underlying rock. Rock melted by impact flowed down into the cracks, producing what are now exposed as ridges of hard rock- the granophyre dykes. One of the dykes located close to the centre of the impact is at Daskop. Its width at the surface is about three meters, but it is hundreds of meters long where it is exposed. These rocks have also been the target of graffiti artists like the San hunters perhaps 2000 years ago..
The Hills uplifted the Dome
The hills surrounding the granite dome reproduced the layered rock formation seen in Johannesburg ( the Witwatersrand). The Vaal River flows westwards through the gaps in the hills.
THE SHATTER CONES
Another signature of an impact is left by the passage of shockwaves through the underlying rock. This produces fractures with a characteristic “ fir tree” pattern.
- The stone village at Askoppies was home to Tswana- speaking farmers in the 1500’s – 1700’s. The stone walls of the village are constructed of fine-grained grey Ventersdorp lavas, rocks that are 2700million years old.
- This area was mined for gold in the 1880’s. However the concentration of gold was much poorer than at Johannesburg, and the diggings were soon abandoned.