The Sudbury Basin (/ˈsʌdbəri/), 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.[1] The crater was formed 1.849 billion years ago in the Paleoproterozoic era.[2]
The basin is located on the Canadian Shield in the city of Greater Sudbury, Ontario. The former municipalities of Rayside-Balfour, Valley East and Capreol 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.[3]
Formation
Onaping Fallback Breccia, polished slab, 15 by 23 cm (6 by 9 in)
The Sudbury basin formed as a result of an impact into the Nuna supercontinent from a meteor approximately 10–15 km (6.2–9.3 mi) in diameter that occurred 1.849 billion years ago[2] in the Paleoproterozoic era.
Debris from the impact was scattered over an area of 1,600,000 km2 (620,000 sq mi) thrown more than 800 km (500 mi); and ejecta — rock fragments ejected by the impact — have been found as far away as Minnesota.[4][5][6]
Models suggest that for such a large impact, debris was most likely scattered globally,[7] but has since been eroded. Its present size is believed to be a smaller portion of a 130 km (81 mi) round crater that the meteor originally created. Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin is the third-largest crater on Earth, after the 300 km (190 mi) Vredefort impact structure in South Africa, and the 180 km (110 mi) Chicxulub crater under Yucatán, Mexico.
Geochemical evidence suggests that the impactor was likely a chondrite asteroid or a comet with a chondritic component.[8]
Structure
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: the Sudbury Igneous Complex (SIC), the Whitewater Group, and footwall brecciated country rocks that include offset 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 a suevite and sedimentary package composed of the Onaping (fallback breccias), 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.[9]
The deformation of the Sudbury structure occurred in five main deformation events (by age in Mega years):
Geological map of the Copper Cliff area, produced in the 1950s.
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[11] 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 impact, including shatter cones[12] and shock-deformed quartz crystals in the underlying rock.[13] Geologists reached consensus by about 1970 that the Sudbury basin was formed by a meteorite impact.[citation needed] In 2014, analysis of the concentration and distribution of siderophile 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.[14][15]
Due to the then-remoteness of the Sudbury area, Salter's discovery did not have much immediate effect. The construction of the Canadian 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 the Murray Mine site, named by owners William and Thomas Murray.[20]
The Vermillion Mine, which was the first in the Basin to be exploited, was the site at which Frank Sperry (a chemist of the Canadian Copper Company) made the first identification in 1889 of the arsenide of platinum which bears his name.[22]
As a result of the 1917 Royal Ontario Nickel Commission, which was chaired by Englishman George Thomas Holloway, the legislative structure of the prospecting trade was significantly altered.[23] Some of the Holloway recommendations were in line with the agitations of Aeneas McCharles a 19th-century prospector and early mine owner.[24]
As a result of these metal deposits, the Sudbury area is one of the world's major mining communities, and has fathered Vale Inco and Falconbridge 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]
Agriculture
Due to the high mineral content of its soil, the floor of the basin is among the best agricultural land in Northern Ontario, with numerous vegetable, berry, and dairy farms located in the valley. However, because of its northern latitude, it is not as productive as agricultural lands in the southern portion of the province. Accordingly, the region primarily supplies products for consumption within Northern Ontario, and is not a major food exporter.[citation needed]
^ abcDavis, Donald W. (January 23, 2008). "Sub-million-year age resolution of Precambrian igneous events by thermal extraction-thermal ionization mass spectrometer Pb dating of zircon: Application to crystallization of the Sudbury impact melt sheet". Geology. 36 (5): 383–386. Bibcode:2008Geo....36..383D. doi:10.1130/G24502A.1.
^Beales, FW; Lozej, GP (1975). "Sudbury Basin Sediments and the Meteoritic Impact Theory of Origin for the Sudbury Structure". Canadian Journal of Earth Sciences. 12 (4): 629–635. Bibcode:1975CaJES..12..629B. doi:10.1139/e75-056.
^Molnár, Ferenc; Watkinson, David H.; Everest, John O. (1999). "Fluid-inclusion characteristics of hydrothermal Cu–Ni–PGE veins in granitic and metavolcanic rocks at the contact of the Little Stobie deposit, Sudbury, Canada". Chemical Geology. 154 (1–4): 279–301. Bibcode:1999ChGeo.154..279M. doi:10.1016/S0009-2541(98)00136-3.
^"Sperrylite". mindat.org and The Hudson Institute of Mineralogy. Retrieved 3 April 2021.
^"GEORGE THOMAS HOLLOWAY". No. Vol. 27, Trans IMM 1917-18, pp.399-400. Northern Mine Research Society. Retrieved 3 April 2021.
^Bemocked of Destiny : The Actual Struggles and Experiences of a Canadian Pioneer, and the Recollections of a Lifetime / By Aeneas McCharles. Toronto : William Briggs, 1908
^Phinney, William (2015). Science Training History of the Apollo Astronauts. NASA SP -2015-626. pp. 247, 252.
External links
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