The Vredefort impact structure is the largest verified

impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surfa ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

. The crater, which has since been eroded away, was around across when it was formed. The remaining structure, comprising the deformed underlying bedrock, is located in present-day Free State province of

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...

. It is named after the town of Vredefort, which is near its centre. The structure's central uplift is known as the Vredefort Dome. The impact structure was formed during the

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

Era, 2.023 billion years (± 4 million years) ago. It is the second-oldest known impact structure on Earth, after

Yarrabubba Yarrabubba Station, often referred to as Yarrabubba, is a pastoral lease that currently operates as a cattle station but has previously operated as a sheep station. It is located about south east of Meekatharra and north east of Cue in ...

. In 2005, the Vredefort Dome was added to the list of

UNESCO The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...

World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for ...

s for its geologic interest.

Formation and structure

The

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

that hit Vredefort is estimated to have been one of the largest ever to strike Earth since the

Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid materia ...

Eon some four billion years ago, originally thought to have been approximately in diameter. The

bolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a ...

that created the

Sudbury Basin The Sudbury Basin (), also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geological structure in Ontario, Canada. It is the third-largest known impact crater or astrobleme on Earth, as well as one of the oldest. The ...

was larger. As of 2022, the bolide was estimated at between in diameter and to have impacted with a vertical velocity of . The original impact structure is estimated to have had a diameter of roughly , but that has been eroded. It would have been larger than the Sudbury Basin and the

Chicxulub crater The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large a ...

. The remaining structure, the "Vredefort Dome", consists of a partial ring of hills in diameter, and is the remains of a dome created by the rebound of rock below the impact site after the collision. The impact structure's age is estimated to be 2.023 billion years (± 4 million years), which places it in the Orosirian Period of the Paleoproterozoic Era. It is the second oldest universally accepted impact structure on Earth. In comparison, it is about 10% older than the Sudbury Basin impact (at 1.849 billion years) and the Yarrabubba impact crater is older than the Vredefort impact structure by about 0.2 billion years.Erickson, T.M., Kirkland, C.L., Timms, N.E., Cavosie, A.J. and Davison, T.M., 2020. ''Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure.'' ''Nature communications'', 11(1), pp.1-8. Other purported older impact structures have either poorly constrained ages ( Dhala impact structure, India)Pati, J.K., Qu, W.J., Koeberl, C., Reimold, W.U., Chakarvorty, M. and Schmitt, R.T., 2017. ''Geochemical evidence of an extraterrestrial component in impact melt breccia from the Paleoproterozoic Dhala impact structure, India.'' ''Meteoritics & Planetary Science'', 52(4), pp.722-736. or highly contentious impact evidence in case of the circa 3.023 billion year old Maniitsoq structure, West GreenlandGarde, A.A., McDonald, I., Dyck, B. and Keulen, N., 2012. ''Searching for giant, ancient impact structures on Earth: the Mesoarchaean Maniitsoq structure, West Greenland.'' ''Earth and Planetary Science Letters'', 337, pp.197-210. and the circa 2.4 billion year old Suavjärvi structure, Russia.Mashchak, M.S. and Naumov, M.V., 2012. ''The Suavjärvi impact structure, NW Russia.'' ''Meteoritics & Planetary Science'', 47(10), pp.1644-1658. Their classification as impact structures remain controversial and unsettled.Reimold, W.U., Ferrière, L., Deutsch, A. and Koeberl, C., 2014. ''Impact controversies: impact recognition criteria and related issues.'' ''Meteoritics & Planetary Science'', 49(5), pp.723-731. The

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

in the centre of the impact structure was originally thought to have been formed by a

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale

shatter cone Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the rang ...

s were discovered in the

bed A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...

of the nearby

Vaal River The Vaal River ( ; Khoemana: ) is the largest tributary of the Orange River in South Africa. The river has its source near Breyten in Mpumalanga province, east of Johannesburg and about north of Ermelo and only about from the Indian Ocean. ...

. This impact structure is one of the few multiple-ringed impact structures on Earth, although they are more common elsewhere in the Solar System. Perhaps the best-known example is Valhalla crater on

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...

's moon Callisto. Earth's

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

has some as well. Geological processes, such as erosion and

plate tectonics Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of larg ...

, have destroyed most multiple-ring impact structures on Earth. The impact distorted the

Witwatersrand Basin The Witwatersrand () (locally the Rand or, less commonly, the Reef) is a , north-facing scarp in South Africa. It consists of a hard, erosion-resistant quartzite metamorphic rock, over which several north-flowing rivers form waterfalls, which ...

which was laid down over a period of 250 million years between 950 and 700 million years before the Vredefort impact. The overlying Ventersdorp lavas and the Transvaal Supergroup which were laid down between 700 and 80 million years before the meteorite strike, were similarly distorted by the formation of the impact structure. The rocks form partial concentric rings around the impact structure's centre today, with the oldest, the

Witwatersrand The Witwatersrand () (locally the Rand or, less commonly, the Reef) is a , north-facing scarp in South Africa. It consists of a hard, erosion-resistant quartzite metamorphic rock, over which several north-flowing rivers form waterfalls, which ...

rocks, forming a semicircle from the centre. Since the Witwatersrand rocks consist of several layers of very hard, erosion-resistant sediments (e.g.

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

s and banded ironstones), they form the prominent arc of hills that can be seen to the northwest of the impact structure's centre in the satellite picture above. The Witwatersrand rocks are followed, in succession, by the Ventersdorp lavas at a distance of about from the centre, and the Transvaal Supergroup, consisting of a narrow band of the Ghaap

Dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

rocks and the Pretoria Subgroup of rocks, which together form a band beyond that.Geological map of South Africa, Lesotho and Swaziland (1970). Council for Geoscience, Geological Survey of South Africa. From about halfway through the Pretoria Subgroup of rocks around the impact structure's centre, the order of the rocks is reversed. Moving outwards towards where the crater rim used to be, the Ghaap Dolomite group resurfaces at from the centre, followed by an arc of Ventersdorp lavas, beyond which, at between from the centre, the Witwatersrand rocks re-emerge to form an interrupted arc of outcrops today. The Johannesburg group is the most famous one because it was here that gold was discovered in 1886. It is thus possible that if it had not been for the Vredefort impact this gold would never have been discovered. The centre of the Vredefort impact structure consists of a granite dome (where it is not covered by much younger rocks belonging to the

Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a peri ...

) which is an exposed part of the

Kaapvaal craton The Kaapvaal Craton (centred on Limpopo Province in South Africa), along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records fr ...

, one of the oldest microcontinents which formed on Earth 3.9 billion years ago. This central peak uplift, or dome, is typical of a complex impact structure, where the liquefied rocks splashed up in the wake of the meteor as it penetrated the surface. File:Earth's geolological timeline.svg, A timeline of the Earth's history indicating when the Vredefort impact structure was formed in relation to some of the other important South African geological events. W indicates when the Witwatersrand Supergroup was laid down, C the

Cape Supergroup The Cape Fold Belt is a fold and thrust belt of late Paleozoic age, which affected the sequence of sedimentary rock layers of the Cape Supergroup in the southwestern corner of South Africa. It was originally continuous with the Ventana Mount ...

, and K the

. The graph also indicates the period during which banded ironstone formations were formed on earth, indicative of an oxygen-free atmosphere. The Earth's crust was wholly or partially molten during the Hadean Eon. One of the first microcontinents to form was the

Kaapvaal Craton The Kaapvaal Craton (centred on Limpopo Province in South Africa), along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records fr ...

, which is exposed at the centre of the Vredefort Dome, and again north of Johannesburg. File:Vredefort crater cross section 2.png, A schematic diagram of a NE (left) to SW (right) cross-section through the 2.020-billion-year-old Vredefort impact structure and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is where the Witwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the impact structure's rim, on the left. Not to scale.

Conservation

The Vredefort Dome World Heritage Site is currently subject to property development, and local owners have expressed concern regarding sewage dumping into the Vaal River and the impact structure. The granting of prospecting rights around the edges of the impact structure has led environmental interests to express fear of destructive mining.

Community

The Vredefort Dome in the centre of the impact structure is home to four towns: Parys, Vredefort,

Koppies Koppies is a small town (railway station) situated near the Renoster River in the Free State province of South Africa. Geography The town is situated 63 km north-east of Kroonstad, 48 km west of Heilbron and 42 km south-south-eas ...

and Venterskroon. Parys is the largest and a tourist hub; both Vredefort and Koppies mainly depend on an agricultural economy. On 19 December 2011, a broadcasting licence was granted by

ICASA The Independent Communications Authority of South Africa (ICASA) is an independent regulatory body of the South African government, established in 2000 by the ICASA Act to regulate both the telecommunications and broadcasting sectors in the publ ...

to a community radio station to broadcast for the Afrikaans- and English-speaking members of the communities within the impact structure. The Afrikaans name ''Koepel'' Stereo (Dome Stereo) refers to the dome and announces its broadcast as KSFM. The station broadcasts on 94.9 MHz FM.

References

External links

Parys South Africa

Impact Cratering Research Group – University of the Witwatersrand

Satellite image of Vredefort impact structure
from

Google Maps Google Maps is a web mapping platform and consumer application offered by Google. It offers satellite imagery, aerial photography, street maps, 360° interactive panoramic views of streets (Street View), real-time traffic conditions, and rou ...

Impact Cratering: an overview of Mineralogical and Geochemical aspects – University of Vienna

Google Earth 3d .KMZ of 25 largest craters
(requires

Google Earth Google Earth is a computer program that renders a 3D computer graphics, 3D representation of Earth based primarily on satellite imagery. The program maps the Earth by superimposition, superimposing satellite images, aerial photography, and geog ...

) {{Impact cratering on Earth Extinction events Impact craters of South Africa Landforms of the Free State (province) Proterozoic impact craters World Heritage Sites in South Africa

Formation and structure

Conservation

Community

See also

References

External links