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Vredefort Dome

South Africa

The scenic Vredefort Mountainland: differential rotation, overturning, and block-faulting of quartzite (lower Witwatersrand Supergroup) caused by the impact. Width of quartzite beds: ~60 meters. Photo: W.U. Reimold.

The scenic Vredefort Mountainland: differential rotation, overturning, and block-faulting of quartzite (lower Witwatersrand Supergroup) caused by the impact. Width of quartzite beds: ~60 meters. Photo: W.U. Reimold.

Geological Period

Paleoproterozoic

Main geological interest

Impact structures and extraterrestrial rocks
Tectonics

Location

North-central South Africa / centered ca. 120 km southwest of Johannesbourg, South Africa
27°00’00”S, 027°18’00”E

The scenic Vredefort Mountainland: differential rotation, overturning, and block-faulting of quartzite (lower Witwatersrand Supergroup) caused by the impact. Width of quartzite beds: ~60 meters. Photo: W.U. Reimold.

Eroded remnant of Earth’s largest impact structure, exposing varied impact-related deformation and melt rocks and a deeply exhumed crustal profile.

As the heart of the largest confirmed hypervelocity impact structure on Earth, the Vredefort Dome provides a unique perspective into the only planetary process that has affected the surfaces of all rocky bodies in our Solar System. Its deep level of exhumation allows an unprecedented view of the catastrophic processes accompanying impact into crustal rocks. Understanding these processes extends beyond these geological phenomena to include planetary-scale environmental consequences of giant impacts and the implications for Life on Earth. This significance was acknowledged by declaration of part of the Vredefort Dome as a UNESCO World Heritage Site in 2005.

Large impact-induced pseudotachylitic breccia in Archean granitoid gneisses in Leeukop quarry (northern core, Vredefort Dome). Outcrop width: ca. 25 meters. Photo: W.U. Reimold.

Large impact-induced pseudotachylitic breccia in Archean granitoid gneisses in Leeukop quarry (northern core, Vredefort Dome). Outcrop width: ca. 25 meters. Photo: W.U. Reimold.

  • Geological description

The 90-kilometer-diameter Vredefort Dome is the deeply eroded remnant of the central uplift of the world’s largest (>250 kilometer diameter) known impact structure. It exposes macroscopic structural evidence (shatter cones, intense fracture patterns, faults, folds) and large dikes of impact melt rock (Vredefort Granophyre) and pseudotachylitic breccia, and rocks containing a range of micro-scale shock metamorphic features, that are all related to the 2.02 Ga impact event. Unusual thermal-metamorphic phenomena attributed to residual heat from the impact are also found in the rocks of the Dome. With an age of 2.02 Ga, the Vredefort Dome is also the second-oldest of the known terrestrial impact structures.
The combination of exceptional differential uplift and rotation that formed the dome and subsequent erosional exhumation by ~10 kilometers has exposed a 20-25 kilometer section through upper and mid-crustal levels of the Archean Kaapvaal craton. Rocks spanning ~1.4 billion years of Earth history, from a >3.1 Ga granite-greenstone Archean Basement Complex to a near-continuous record of Neoarchean to Paleoproterozoic sedimentation and volcanism between 3 and 2.1 Ga (Dominion Group and Witwatersrand, Ventersdorp and Transvaal supergroups) provide an exceptional record of early crustal evolution.
The Vredefort impact structure extends over much of the gold-bearing Witwatersrand Basin, and the impact event was integral to the preservation of this exceptional resource.

  • Scientific research and tradition

An exceptional archive of scientific knowledge and tradition, and of evolution and contestation of scientific ideas, is provided by the more than 400 research articles published since 1878 on the geology and natural resources of the Vredefort Dome, including several by some of the most prominent geoscientists of their times.

Schematic geological map of the Vredefort Dome. Source: W.U. Reimold.

Schematic geological map of the Vredefort Dome. Source: W.U. Reimold.

  • Reference

Allen, N.H. et al. (2022) ‘A Revision of the Formation Conditions of the Vredefort Crater’, Journal of Geophysical Research: Planets, 127(8), p. e2022JE007186. Available at: https://doi.org/10.1029/2022JE007186.

Gibson, R.L. (2019) ‘The Mesoarchaean Basement Complex of the Vredefort Dome—A Mid-Crustal Section Through the Central Kaapvaal Craton Exposed by Impact’, in A. Kröner and A. Hofmann (eds) The Archaean Geology of the Kaapvaal Craton, Southern Africa. Cham: Springer International Publishing (Regional Geology Reviews), pp. 109–132. Available at: https://doi.org/10.1007/978-3-319-78652-0_5.

Gibson, R.L. and Reimold, W.U. (2008) Geology of the Vredefort impact structure: a guide to sites of interest. Pretoria: Council for Geoscience (Memoir, 97).

Gottwald, M., Kenkmann, T. and Reimold, W.U. (2020) Terrestrial impact structures: the TanDEM-X Atlas. München, Germany: Verlag Dr. Friedrich Pfeil.

Grieve, R.A.F. et al. (2008) ‘Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation’, Meteoritics & Planetary Science, 43(5), pp. 855–882. Available at: https://doi.org/10.1111/j.1945-5100.2008.tb01086.x.

Reimold, W.U. and Gibson, R.L. (2010) Meteorite Impact!: The Danger from Space and South Africa’s Mega-Impact The Vredefort Structure. Berlin, Heidelberg: Springer. Available at: https://doi.org/10.1007/978-3-642-10464-0.

  • Author(s)

W. Uwe Reimold.
University of Brasília, Brazil.

Roger L. Gibson.
University of the Witwatersrand, Johannesburg, South Africa.

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