Overberg Geoscientists Group
2020 Mya
Vredefort Dome
The Vredefort Dome is the remnants of the largest known impact crater on Earth. Originally the crater was around 300km in diameter.
The Asteroid that impacted the Earth some 2020 million years ago was around 20km in diameter. It was only confirmed in the 1990s that this was the remnants of an impact. Rocks like the ones in the image were found. They are ‘pseudotachylites’ This means that the impact was of such magnitude that it melted the country rock and fractured debris was included in the melted material.
Pseudotachylite
There is also evidence of shattered rock, producing ‘shattercones’ formed as concentric conical surfaces caused by the intense shock wave passing through the rock mass as the asteroid impacted.
The actual dome that remains is merely the central rebound of the impact. Analogous to the droplet in te image.
The central dome is some 75km wide and basement material was brought up from some 20km down to form it.
Further reading:
McCarthy, Terence (2005). The Story of Earth & Life. Struik Publishers. pp. 89–90, 102–107, 134–136. ISBN 978-1-77007-148-3.
Allen, Natalie H.; Nakajima, Miki; Wünnemann, Kai; Helhoski, Søren; Trail, Dustin (2022). "A Revision of the Formation Conditions of the Vredefort Crater". Journal of Geophysical Research: Planets. 127 (8): e2022JE007186.
University of Rochester (26 September 2022). "The asteroid that formed Vredefort crater was bigger than previously believed". Science X. Archived from the original on 26 September 2022.
Norman, Nick; Whitfield, Gavin (2006). Geological Journeys. Struik Publishers. pp. 38–49, 60–61. ISBN 978-1-77007-062-2. OCLC 974035410.
"Vredefort". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton.
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D J Mourant Aug 2023