| Sudbury Basin | |
|---|---|
| Sudbury Structure | |
 NASA World Wind satellite image of the Sudburyastrobleme | |
| Impact crater/structure | |
| Confidence | Confirmed |
| Diameter | 130 km (81 mi) |
| Age | 1849 Ma Paleoproterozoic |
| Exposed | Yes |
| Drilled | Yes |
| Bolide type | Chondrite |
| Location | |
| Coordinates | 46°36′N81°11′W / 46.600°N 81.183°W /46.600; -81.183 |
| Country | Canada |
| Province | Ontario |
  Location of the crater in Canada | |
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TheSudbury Basin (/ˈsʌdbəri/), also known asSudbury Structure or theSudbury Nickel Irruptive, is a majorgeological structure inOntario, Canada. It is among the oldest- and largest-knownimpact structures on Earth.[1] The structure, the eroded remnant of animpact crater, was formed by the impact of an asteroid 1.849 billion years ago in thePaleoproterozoic era.[2] The ores of the Sudbury Basin are known to containnickel,copper,gold,silver,platinum,palladium,rhodium,iridium, andruthenium.[3]
The basin is located on theCanadian Shield in the city ofGreater Sudbury,Ontario. The former municipalities ofRayside-Balfour,Valley East andCapreol lie within the Sudbury Basin, which is referred to locally as "The Valley". The urban core of the former city of Sudbury lies on the southern outskirts of the basin.
An Ontario Historical Plaque was erected by the province to commemorate the discovery of the Sudbury Basin.[4]
The Sudbury basin formed as a result of animpact into theNuna supercontinent from a largeimpactor body approximately 10–15 km (6.2–9.3 mi) in diameter that occurred 1.849 billion years ago[2] in thePaleoproterozoic era.
Debris from the impact was scattered over an area of 1,600,000 km2 (620,000 sq mi) and thrown more than 800 km (500 mi);ejecta—rock fragments ejected by the impact—have been found as far away asMinnesota.[5][6][7]
Models suggest that for such a large impact, debris was most likely scattered globally,[8] but has since been eroded. Its present size is believed to be a smaller portion of a 130-kilometre (81 mi) round crater that themeteor originally created. Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin is among the largest-known craters on Earth, after the 300-kilometre (190 mi)Vredefort impact structure inSouth Africa, and the 180-kilometre (110 mi)Chicxulub crater underYucatán,Mexico.
Geochemical evidence suggests that the impactor was likely achondrite asteroid or a comet with a chondritic component.[9]
The full extent of the Sudbury Basin is 62 km (39 mi) long, 30 km (19 mi) wide, and 15 km (9.3 mi) deep, although the modern ground surface is much shallower.[citation needed]
The main units characterizing the Sudbury Structure can be subdivided into three groups: theSudbury Igneous Complex (SIC), the Whitewater Group, and footwall brecciated country rocks that includeoffset dikes and the Sub layer. The SIC is believed to be a stratified impact melt sheet composed from the base up of sub layer norite, mafic norite, felsic norite, quartz gabbro, and granophyre.[citation needed]
The Whitewater Group consists of asuevite and sedimentary package composed of the Onaping (fallbackbreccias), Onwatin, and Chelmsford Formations in stratigraphic succession. Footwall rocks, associated with the impact event, consist of Sudbury Breccia (pseudotachylite), footwall breccia, radial and concentric quartz dioritic breccia dikes (polymict impact melt breccias), and the discontinuous sub layer.[citation needed]
Because considerable erosion has occurred since the Sudbury event, an estimated 6 km (3.7 mi) in the North Range, it is difficult to directly constrain the actual size of the diameter of the original transient cavity, or the final rim diameter.[10]
The deformation of the Sudbury structure occurred in five main deformation events (by age in millions of years):
Some 1.8 billion years of weathering and deformation made it difficult to prove that a meteorite was the cause of the Sudbury geological structures. A further difficulty in proving that the Sudbury complex was formed by meteorite impact rather than by ordinary igneous processes was that the region was volcanically active at around the same time as the impact, and some weathered volcanic structures can look like meteorite collision structures. Since its discovery, a layer of breccia has been found associated with the impact event,[12] and stressed rock formations have been fully mapped.
Reports published in the late 1960s described geological features that were said to be distinctive of meteorite impacts, includingshatter cones[13] and shock-deformed quartz crystals in the underlying rock.[14] Geologists reached a consensus by about 1970 that the Sudbury basin was formed by a meteorite impact.[citation needed] In 2014, analysis of the concentration and distribution ofsiderophile elements as well as the size of the area where the impact melted the rock indicated that a comet, rather than an asteroid, most likely caused the crater.[15][16]
The Sudbury Basin is located near a number of other geological structures, including theTemagami Magnetic Anomaly, theLake Wanapitei impact crater, the western end of theOttawa-Bonnechere Graben, theGrenville Front Tectonic Zone, and the eastern end of theGreat Lakes Tectonic Zone, but the structures are not directly related to one another in the sense of resulting from the same geological processes.[citation needed]
The large impact crater filled withmagma containingnickel,copper,palladium,gold, theplatinum group, and othermetals.[17] This magma formed intopyrrhotite,chalcopyrite, andpentlandite rocks,[18][19] as well ascubanite andmagnetite.[20]
In 1856, while surveying a baseline westward fromLake Nipissing, provincial land surveyorAlbert Salter locatedmagnetic abnormalities in the area that were strongly suggestive of mineral deposits, especially near what later became theCreighton Mine.[21] The area was examined byAlexander Murray of theGeological Survey of Canada,[21] who confirmed "the presence of an immense mass of magnetic trap".[22]
Due to the then-remoteness of the Sudbury area, Salter's discovery did not have much immediate effect. The construction of theCanadian Pacific Railway through the area, however, made mineral exploration more feasible. The development of a mining settlement occurred in 1883 after blasting at the railway construction site revealed a large concentration of nickel and copper ore at what is now theMurray Mine site, named by owners William and Thomas Murray.[21]
TheVermillion Mine, which was the first in the Basin to be exploited, was the site at which Frank Sperry (a chemist of theCanadian Copper Company) made the first identification in 1889 of thearsenide of platinum whichbears his name.[23]
As a result of the 1917 Royal Ontario Nickel Commission, which was chaired by EnglishmanGeorge Thomas Holloway, the legislative structure of the prospecting trade was significantly altered.[24] Some of the Holloway recommendations were in line with the advocacy ofAeneas McCharles, a 19th-century prospector and early mine owner.[25]
As a result of these metal deposits, the Sudbury area is one of the world's majormining communities, and has fatheredVale Inco andFalconbridge Xstrata. The Basin is one of the world's largest suppliers of nickel and copper ores. Most of these mineral deposits are found on its outer rim.[citation needed]
This list was collected from the 1917 topographic map of the Sudbury Basin, located at right.
Most soils in the Sudbury Basin are acidic and sandy; where well-drained, they usually belong to thePodzol great soil group. Poor drainage results ingleysols andpeats. Regardless of drainage or classification, the Basin has deeper soils than the surrounding terrain, much of which is mapped as Rockland (a combination of frequent bedrock outcrops and shallow soil). Consequently, considerable areas in the Basin have been cleared for agriculture. The best soils, mapped as Azilda series and Bradley series, occur aroundChelmsford.[26]
NASA used the site to train theApollo astronauts in recognizing rocks formed as the result of a very large impact, such asbreccias. Those who used this training on the Moon includeApollo 15'sDavid Scott andJames Irwin,Apollo 16'sJohn Young andCharlie Duke, andApollo 17'sGene Cernan andJack Schmitt. Notable geologist instructors includedWilliam R. Muehlberger.[27]
