Sudbury Basin
Encyclopedia
The Sudbury Basin, also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geologic
structure in Ontario
, Canada
. It is the second-largest known impact crater
or astrobleme on Earth
, as well as one of the oldest.
The basin is located on the Canadian Shield
in the city of Greater Sudbury, Ontario
. The former municipalities of Rayside-Balfour and Valley East 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.
The Sudbury Basin is located near a number of other geological structures, including the Temagami Magnetic Anomaly
, the Lake Wanapitei
impact crater, the western end of the Ottawa-Bonnechere Graben
, and the eastern end of the Great Lakes Tectonic Zone
although none of the structures are directly related to each other in the sense of resulting from the same geophysical processes.
from a bolide approximately 10–15 km (6.2–9.3 mi) in diameter that occurred 1.849 billion years ago in the Paleoproterozoic
era.
Debris from the impact was scattered over an area of 1600000 km² (617,763.5 sq mi) and traveled over 800 km (497.1 mi) away — rock fragments ejected by the impact have been found as far as Minnesota
(though models suggest that for such a large impact, debris was most likely scattered globally, but has since been eroded away). Its present size is believed to be a smaller portion of a 250 km (155.3 mi) round crater that the bolide originally created.
Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin would then be the second-largest crater on Earth, after the 300 km (186.4 mi) Vredefort crater
in South Africa
, and larger than the 170 km (105.6 mi) Chicxulub crater
in Yucatán
, Mexico
.
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 Sublayer. The SIC is believed to be a stratified impact melt sheet composed from the base up of sublayer norite, mafic norite, felsic norite, quartz gabbro, and granophyre.
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 sublayer.
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 Sudbury crater, whether it being the diameter of the original transient cavity, or the final rim diameter.
The deformation of the Sudbury structure occurred in five main deformation events (by age):
Considering how old the evidence is for a meteor impact, some 1.8 billions of years of weathering and other geological processes made it difficult to prove with 1970s era technology that a meteor was the cause of the Sudbury geological structures. Since then an ash and conglomerate layer has been found associated with the impact event and stressed rock formations have been fully mapped.
The cause of the ongoing difficulty with proof of the meteor event was that the region was volcanically active around the same time as the impact—and some weathered volcanic structures can look like meteor collision structures given the right conditions.
containing nickel
, copper
, platinum
, palladium
, gold
, and other metal
s. In 1856 while surveying a baseline westward from Lake Nipissing
, provincial land surveyor Albert Salter
located magnetic abnormalities in the area that were strongly suggestive of mineral deposits. The area was then examined by Alexander Murray of the Geological Survey of Canada, who confirmed "the presence of an immense mass of magnetic trap".
Due to the then-remoteness of the Sudbury area, Salter's discovery did not have much immediate impact. The later 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 connected to the railway construction revealed a large concentration of nickel and copper ore at the Murray Mine
site.
As a result of these metal deposits, the Sudbury area is one of the world's major mining
communities. The region is one of the world's largest suppliers of nickel and copper ores. Most of these mineral deposits are found on the outer rim of the basin.
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. Due to its northern latitude, it is not as fertile 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.
An Ontario Historical Plaque was erected by the province to commemorate the discovery of the Sudbury Basin.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
structure in Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. It is the second-largest known impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
or astrobleme on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, as well as one of the oldest.
The basin is located on the Canadian Shield
Canadian Shield
The Canadian Shield, also called the Laurentian Plateau, or Bouclier Canadien , is a vast geological shield covered by a thin layer of soil that forms the nucleus of the North American or Laurentia craton. It is an area mostly composed of igneous rock which relates to its long volcanic history...
in the city of Greater Sudbury, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. The former municipalities of Rayside-Balfour and Valley East 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.
The Sudbury Basin is located near a number of other geological structures, including the Temagami Magnetic Anomaly
Temagami Magnetic Anomaly
The Temagami Magnetic Anomaly, also called the Temagami Anomaly or the Wanapitei Anomaly, is a large buried geologic structure in Ontario, Canada, stretching from Lake Wanapitei in the west to Bear Island in Lake Temagami....
, the Lake Wanapitei
Lake Wanapitei
Lake Wanapitei occupies a meteorite crater in Sudbury, Ontario, Canada. It is located near the large Sudbury meteorite crater but is not related to it....
impact crater, the western end of the Ottawa-Bonnechere Graben
Ottawa-Bonnechere Graben
The Ottawa-Bonnechere Graben , with its branch the Timiskaming Graben, is an ancient rift valley in the Canadian Shield of Northeastern Ontario and Quebec, Canada. This rift valley was formed when the Earth's crust moved downward about a kilometre between two major fault zones known as the Mattawa...
, and the eastern end of the Great Lakes Tectonic Zone
Great Lakes tectonic zone
During the Late Archean Eon the Algoman orogeny added landmass to the Superior province by volcanic activity and continental collision along a boundary that stretches from present-day South Dakota, U.S., into the Sudbury, Ontario, Canada, Lake Huron region....
although none of the structures are directly related to each other in the sense of resulting from the same geophysical processes.
Formation and structure
The full extent of the Sudbury Basin is 62 km (38.5 mi) long, 30 km (18.6 mi) wide and 15 km (9.3 mi) deep, although the modern ground surface is much shallower. The basin formed as an impactImpact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
from a bolide approximately 10–15 km (6.2–9.3 mi) in diameter that occurred 1.849 billion years ago in the Paleoproterozoic
Paleoproterozoic
The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
era.
Debris from the impact was scattered over an area of 1600000 km² (617,763.5 sq mi) and traveled over 800 km (497.1 mi) away — rock fragments ejected by the impact have been found as far as Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
(though models suggest that for such a large impact, debris was most likely scattered globally, but has since been eroded away). Its present size is believed to be a smaller portion of a 250 km (155.3 mi) round crater that the bolide originally created.
Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin would then be the second-largest crater on Earth, after the 300 km (186.4 mi) Vredefort crater
Vredefort crater
Vredefort crater is the largest verified impact crater on Earth. It is located in the Free State Province of South Africa and named after the town of Vredefort, which is situated near its centre. The site is also known as the Vredefort dome or Vredefort impact structure...
in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, and larger than the 170 km (105.6 mi) Chicxulub crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...
in Yucatán
Yucatán
Yucatán officially Estado Libre y Soberano de Yucatán is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 106 municipalities and its capital city is Mérida....
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
.
The main units characterizing the Sudbury Structure can be subdivided into three groups: the Sudbury Igneous Complex
Sudbury Igneous Complex
The Sudbury Igneous Complex is a 1,844 million year-old impact melt sheet in Greater Sudbury, Northern Ontario, Canada. It is part of the Sudbury Basin impact structure, and is classified as a lopolith.-References:*...
(SIC), the Whitewater Group, and footwall brecciated country rocks that include offset dikes
Sudbury dike swarm
The Sudbury dike swarm, also called the Sudbury dikes, is a Mesoproterozoic dike swarm in northeastern Ontario, Canada. With an age of 1,238 million years, it is younger than the Sudbury Basin impact event and predates the impact event that formed Lake Wanapitei.-See also:*Volcanism of...
and the Sublayer. The SIC is believed to be a stratified impact melt sheet composed from the base up of sublayer norite, mafic norite, felsic norite, quartz gabbro, and granophyre.
The Whitewater Group consists of a suevite
Suevite
Suevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event...
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
Pseudotachylite
Pseudotachylite is a fault rock that has the appearance of the basaltic glass, tachylyte. It is dark in color and has a glassy appearance. However, the glass has normally been completely devitrified into very fine-grained material with radial and concentric clusters of crystals...
), footwall breccia, radial and concentric quartz dioritic breccia dikes (polymict impact melt breccias), and the discontinuous sublayer.
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 Sudbury crater, whether it being the diameter of the original transient cavity, or the final rim diameter.
The deformation of the Sudbury structure occurred in five main deformation events (by age):
- formation of the Sudbury Igneous ComplexSudbury Igneous ComplexThe Sudbury Igneous Complex is a 1,844 million year-old impact melt sheet in Greater Sudbury, Northern Ontario, Canada. It is part of the Sudbury Basin impact structure, and is classified as a lopolith.-References:*...
(1849 Ma) - the Penokean orogenyPenokean orogenyThe Penokean orogeny was a mountain-building episode that occurred in the early Proterozoic about 1.85 to 1.84 billion years ago, in the area of North America that would eventually become Minnesota, Wisconsin, Michigan and Ontario...
(1890-1830 Ma) - the Mazatzal orogeny (1700-1600 Ma)
- the Grenville orogenyGrenville orogenyThe Grenville Orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland...
(1400 - 1000 Ma) - the Lake WanapiteiLake WanapiteiLake Wanapitei occupies a meteorite crater in Sudbury, Ontario, Canada. It is located near the large Sudbury meteorite crater but is not related to it....
impact (37 Ma)
Disputes over origin
Even as late as the mid-1970s, geologists were not fully certain of the Sudbury basin having meteor origins. The educational television programme Planet of Man—created for Canadian universities to use in introductory geology classes—mooted the possible volcanic origins of the Sudbury geological structures.Considering how old the evidence is for a meteor impact, some 1.8 billions of years of weathering and other geological processes made it difficult to prove with 1970s era technology that a meteor was the cause of the Sudbury geological structures. Since then an ash and conglomerate layer has been found associated with the impact event and stressed rock formations have been fully mapped.
The cause of the ongoing difficulty with proof of the meteor event was that the region was volcanically active around the same time as the impact—and some weathered volcanic structures can look like meteor collision structures given the right conditions.
Modern uses
The large impact crater filled with magmaMagma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
containing nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
, gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
, and other metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s. In 1856 while surveying a baseline westward from Lake Nipissing
Lake Nipissing
Lake Nipissing is a lake in the Canadian province of Ontario. It has a surface area of , a mean elevation of above sea level, and is located between the Ottawa River and Georgian Bay. Excluding the Great Lakes, Lake Nipissing is the fifth-largest lake in Ontario. It is relatively shallow for a...
, provincial land surveyor Albert Salter
Albert Salter
Albert Salter was a provincial land surveyor in Ontario in the mid-19th century. He is historically most notable for having discovered magnetic abnormalities at what is now Creighton Mine in Greater Sudbury, while surveying a baseline westward from Lake Nipissing in 1856...
located magnetic abnormalities in the area that were strongly suggestive of mineral deposits. The area was then examined by Alexander Murray of the Geological Survey of Canada, who confirmed "the presence of an immense mass of magnetic trap".
Due to the then-remoteness of the Sudbury area, Salter's discovery did not have much immediate impact. The later construction of the Canadian Pacific Railway
Canadian Pacific Railway
The Canadian Pacific Railway , formerly also known as CP Rail between 1968 and 1996, is a historic Canadian Class I railway founded in 1881 and now operated by Canadian Pacific Railway Limited, which began operations as legal owner in a corporate restructuring in 2001...
through the area, however, made mineral exploration more feasible. The development of a mining settlement occurred in 1883 after blasting connected to the railway construction revealed a large concentration of nickel and copper ore at the Murray Mine
Murray Mine
Murray Mine is a defunct nickel and copper mine in Greater Sudbury, Ontario. It was the site of the original ore discovery that led to the launch of mining operations in the Sudbury area....
site.
As a result of these metal deposits, the Sudbury area is one of the world's major mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
communities. The region is one of the world's largest suppliers of nickel and copper ores. Most of these mineral deposits are found on the outer rim of the basin.
Due to the high mineral content of its soil, the floor of the basin is among the best agricultural
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
land in Northern Ontario
Northern Ontario
Northern Ontario is a region of the Canadian province of Ontario which lies north of Lake Huron , the French River and Lake Nipissing. The region has a land area of 802,000 km2 and constitutes 87% of the land area of Ontario, although it contains only about 6% of the population...
, with numerous vegetable
Vegetable
The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....
, berry
Berry
The botanical definition of a berry is a fleshy fruit produced from a single ovary. Grapes are an example. The berry is the most common type of fleshy fruit in which the entire ovary wall ripens into an edible pericarp. They may have one or more carpels with a thin covering and fleshy interiors....
, and dairy
Dairy
A dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned...
farms located in the valley. Due to its northern latitude, it is not as fertile 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.
An Ontario Historical Plaque was erected by the province to commemorate the discovery of the Sudbury Basin.
External links
- Earth Impact Database
- Aerial Exploration of the Sudbury Crater
- Fallbrook Gem and Mineral Society - Sudbury Structure page
- 190Pt– 186Os and 187Re– 187Os systematics of the Sudbury Igneous Complex, Ontario. Study by John W. Morgan et al. Geochimica et Cosmochimica Acta, Vol. 66, No. 2, pp. 273–290, 2002.