Canadian Shield

Last updated
Canadian Shield
Stratigraphic range: Precambrian
Type Shield
Unit of North American craton
Sub-units Laurentian Upland
Kazan [1]
Area8,000,000 km2 [2]
Location
Coordinates 52°00′N71°00′W / 52.000°N 71.000°W / 52.000; -71.000
Region North America
CountryCanada
United States
Greenland
Canada geological map.JPG
The Canadian Shield is a broad region of Precambrian rock (pictured in shades of red) that encircles Hudson Bay. It spans eastern, northeastern, and east-central Canada and the upper midwestern United States.

The Canadian Shield (French : Bouclier canadien [bukljekanadjɛ̃] ), also called the Laurentian Shield or the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the ancient geologic core of the North American continent. Glaciation has left the area with only a thin layer of soil, through which exposures of igneous bedrock resulting from its long volcanic history are frequently visible. [3] As a deep, common, joined bedrock region in eastern and central Canada, the shield stretches north from the Great Lakes to the Arctic Ocean, covering over half of Canada and most of Greenland; it also extends south into the northern reaches of the continental United States.

Contents

Geographical extent

The Canadian Shield is a physiographic division comprising four smaller physiographic provinces: the Laurentian Upland, Kazan Region, Davis and James. [1] The shield extends into the United States as the Adirondack Mountains (connected by the Frontenac Axis) and the Superior Upland. The Canadian Shield is a U-shaped subsection of the Laurentia craton signifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils. The age of the Canadian Shield is estimated to be 4.28 Ga. The Canadian Shield once had jagged peaks, higher than any of today's mountains, but millions of years of erosion have changed these mountains to rolling hills. [4]

The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic Eon that were progressively amalgamated during the interval 2.45–1.24 Ga, with the most substantial growth period occurring during the Trans-Hudson orogeny, between c. 1.90–1.80 Ga. [5] The Canadian Shield was the first part of North America to be permanently elevated above sea level and has remained almost wholly untouched by successive encroachments of the sea upon the continent. It is the Earth's greatest area of exposed Archean rock. The metamorphic base rocks are mostly from the Precambrian (between 4.5 Ga and 540 Ma) and have been repeatedly uplifted and eroded. Today it consists largely of an area of low relief 300–610 m (980–2,000 ft) above sea level with a few monadnocks and low mountain ranges (including the Laurentian Mountains) probably eroded from the plateau during the Cenozoic Era. During the Pleistocene Epoch, continental ice sheets depressed the land surface (creating Hudson Bay) but also tilted up its northeastern "rim" (the Torngat), scooped out thousands of lake basins, and carried away much of the region's soil. The northeastern portion, however, became tilted up so that, in northern Labrador and Baffin Island, the land rises to more than 1,500 metres (5,000 feet) above sea level.

When the Greenland section is included, the Canadian Shield is approximately circular, bounded on the northeast by the northeast edge of Greenland, with Hudson Bay in the middle. It covers much of Greenland, all of Labrador and the Great Northern Peninsula of Newfoundland, most of Quebec north of the St. Lawrence River, much of Ontario including northern sections of the Ontario Peninsula, the Adirondack Mountains [6] of New York, the northernmost part of Lower Michigan and all of Upper Michigan, northern Wisconsin, northeastern Minnesota, the central and northern portions of Manitoba, northern Saskatchewan, a small portion of northeastern Alberta, [7] mainland Northwest Territories to the east of a line extended north from the Saskatchewan-Alberta border, most of Nunavut's mainland and, of its Arctic Archipelago, Baffin Island and significant bands through Somerset, Southampton, Devon and Ellesmere islands. [2] In total, the exposed area of the shield covers approximately 8,000,000 km2 (3,100,000 sq mi). The true extent of the shield is greater still and stretches from the Western Cordillera in the west to the Appalachians in the east and as far south as Texas, but these regions are overlaid with much younger rocks and sediment.

Flin Flon Wilderness and Outcrop.jpg
Panorama of Canadian Shield geography in the Flin Flon, Manitoba, region. Big Island Lake is in the background.

Geology

The Canadian Shield is among the oldest geologic areas on Earth, with regions dating from 2.5 to 4.2 billion years. [8] The multitude of rivers and lakes in the region is classical example of a deranged drainage system, caused by the watersheds of the area being disturbed by glaciation and the effect of post-glacial rebound. [9] The shield was originally an area of very large, very tall mountains (about 12,000 m or 39,000 ft) [10] with much volcanic activity, but the area was eroded to nearly its current topographic appearance of relatively low relief over 500 Ma. [11] [12] Erosion has exposed the roots of the mountains, which take the form of greenstone belts in which belts of volcanic rock that have been altered by metamorphism are surrounded by granitic rock. These belts range in age from 3.6 to 2.7 Ga. [13] Much of the granitic rock belongs to the distinctive tonalite–trondhjemite–granodiorite family of rocks, which are characteristic of Archean continental crust. [14] Many of Canada's major ore deposits are associated with greenstone belts. [15]

The Sturgeon Lake Caldera in Kenora District, Ontario, is one of the world's best preserved mineralized Neoarchean caldera complexes, which is 2.7 Ga. [16] The Canadian Shield also contains the Mackenzie dike swarm, which is the largest dike swarm known on Earth. [17] The North American craton is the bedrock forming the heart of the North American continent, and the Canadian Shield is the largest exposed part of the craton's bedrock. The Canadian Shield is part of an ancient continent called Arctica, which was formed about 2.5 Ga during the Neoarchean era.

Mountains have deep roots and float on the denser mantle much like an iceberg at sea. As mountains erode, their roots rise and are eroded in turn. The rocks that now form the surface of the shield were once far below the Earth's surface. The high pressures and temperatures at those depths provided ideal conditions for mineralization. Although these mountains are now heavily eroded, many large mountains still exist in Canada's far north called the Arctic Cordillera. This is a vast, deeply dissected mountain range, stretching from northernmost Ellesmere Island to the northernmost tip of Labrador. The range's highest peak is Nunavut's Barbeau Peak at 2,616 metres (8,583 ft) above sea level. [18] Precambrian rock is the major component of the bedrock.

Ecology

Typical shield landscape in a southern Ontario region with very few old growth trees, due to a history of logging and fires. Black River, Queen Elizabeth II Wildlands Provincial Park. BlackRiver1.JPG
Typical shield landscape in a southern Ontario region with very few old growth trees, due to a history of logging and fires. Black River, Queen Elizabeth II Wildlands Provincial Park.

The current surface expression of the shield is one of very thin soil lying on top of the bedrock, with many bare outcrops. This arrangement was caused by severe glaciation during the ice ages that covered the shield and scraped the rock clean. The lowlands of the Canadian Shield have a very dense soil that is not suitable for forestation; it also contains many marshes and bogs (muskegs). The rest of the region has coarse soil that does not retain moisture well and is frozen with permafrost throughout the year. Forests are not as dense in the north.

The shield is covered in parts by vast boreal forests in the south that support natural ecosystems as well as a major logging industry. The boreal forest area gives way to the Eastern Canadian Shield taiga that covers northern Quebec and most of Labrador. The Midwestern Canadian Shield forests that run westwards from Northwestern Ontario have boreal forests that give way to taiga in the most northerly parts of Manitoba and Saskatchewan. Hydrologic drainage is generally poor, the soil compacting effects of glaciation being one of the many causes. Tundra typically prevails in the northern regions.

Many mammals such as beaver, caribou, white-tailed deer, moose, wolves, wolverines, weasels, mink, otters, grizzly bear, polar bears and black bears are present. [19] In the case of polar bears (Ursus maritimus), the shield area contains many of their denning locations, such as the Wapusk National Park. [20] The many lakes and rivers on the shield contain a plentiful quantity of different sports fish species, including walleye, northern pike, lake trout, yellow perch, whitefish, brook trout, arctic grayling, and many types of baitfish. [21] The water surfaces are also home to many waterfowl, most notably Canada geese, loons and gulls. [22] The vast forests contain a myriad population of other birds, including ravens and crows, predatory birds and many songbirds.

Mining and economics

The Canadian Shield is one of the world's richest areas in terms of mineral ores. It is filled with substantial deposits of nickel, gold, silver, and copper. There are many mining towns extracting these minerals. The largest, and one of the best known, is Sudbury, Ontario. Sudbury is an exception to the normal process of forming minerals in the shield since the Sudbury Basin is an ancient meteorite impact crater. Ejecta from the meteorite impact was found in the Rove Formation in May 2007. The nearby but less-known Temagami Magnetic Anomaly has striking similarities to the Sudbury Basin. This suggests it could be a second metal-rich impact crater. [23] In northeastern Quebec, the giant Manicouagan Reservoir is the site of an extensive hydroelectric project (Manic-cinq, or Manic-5). This is one of the largest-known meteorite impact craters on Earth, though not as large as the Sudbury crater.

The Flin Flon greenstone belt in central Manitoba and east-central Saskatchewan "is one of the largest Paleoproterozoic volcanic-hosted massive sulfide (VMS) districts in the world, containing 27 copper-zinc-(gold) deposits from which more than 183 million tonnes of sulfide have been mined." [24] The portion in the Northwest Territories has recently been the site of several major diamond discoveries. The kimberlite pipes in which the diamonds are found are closely associated with cratons, which provide the deep lithospheric mantle required to stabilize diamond as a mineral. The kimberlite eruptions then bring the diamonds from over 150 kilometres (93 mi) depth to the surface. The Ekati and Diavik mines are actively mining kimberlite diamonds.

See also

Related Research Articles

<span class="mw-page-title-main">Baltic Shield</span> Ancient segment of Earths crust

The Baltic Shield is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archean and Proterozoic gneisses and greenstone which have undergone numerous deformations through tectonic activity. It contains the oldest rocks of the European continent with a thickness of 250–300 km.

<span class="mw-page-title-main">Kenorland</span> Hypothetical Neoarchaean supercontinent from about 2.8 billion years ago

Kenorland is a hypothetical Neoarchean supercontinent. If it existed, it would have been one of the earliest known supercontinents on Earth. It is thought to have formed during the Neoarchaean Era c. 2.72 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust. It comprised what later became Laurentia, Baltica, Western Australia and Kalaharia.

<span class="mw-page-title-main">Greenstone belt</span> Zone of variably metamorphosed rocks occurring in Archaean and Proterozoic cratons

Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.

<span class="mw-page-title-main">Yilgarn Craton</span> Large craton in Western Australia

The Yilgarn Craton is a large craton that constitutes a major part of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts. Zircon grains in the Jack Hills, Narryer Terrane have been dated at ~4.27 Ga, with one detrital zircon dated as old as 4.4 Ga.

<span class="mw-page-title-main">Churchill Craton</span> Geologic region in Canada

The Churchill Craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary magmatic events. The Western Churchill province is the part of the Churchill Craton that is exposed north and west of the Hudson Bay. The Archean Western Churchill province contributes to the complicated and protracted tectonic history of the craton and marks a major change in the behaviour of the Churchill Craton with many remnants of Archean supracrustal and granitoid rocks.

<span class="mw-page-title-main">Geology of Minnesota</span>

The geology of Minnesota comprises the rock, minerals, and soils of the U.S. state of Minnesota, including their formation, development, distribution, and condition.

<span class="mw-page-title-main">Geology of the Rocky Mountains</span>

The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through central New Mexico and which is part of the great mountain system known as the North American Cordillera.

<span class="mw-page-title-main">Trans-Hudson orogeny</span> Mountain-building event in North America

The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton, forging the initial North American continent. It gave rise to the Trans-Hudson orogen (THO), or Trans-Hudson Orogen Transect (THOT), which is the largest Paleoproterozoic orogenic belt in the world. It consists of a network of belts that were formed by Proterozoic crustal accretion and the collision of pre-existing Archean continents. The event occurred 2.0–1.8 billion years ago.

<span class="mw-page-title-main">Laurentia</span> Craton forming the geological core of North America

Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and the Hebridean Terrane in northwest Scotland. During other times in its past, Laurentia has been part of larger continents and supercontinents and consists of many smaller terranes assembled on a network of early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.

<span class="mw-page-title-main">Geology of Saskatchewan</span>

The geology of Saskatchewan can be divided into two main geological regions, the Precambrian Canadian Shield and the Phanerozoic Western Canadian Sedimentary Basin. Within the Precambrian shield exists the Athabasca sedimentary basin. Meteorite impacts have altered the natural geological formation processes. The prairies were most recently affected by glacial events in the Quaternary period.

The West African Craton (WAC) is one of the five cratons of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania Craton. Cratons themselves are tectonically inactive, but can occur near active margins, with the WAC extending across 14 countries in Western Africa, coming together in the late Precambrian and early Palaeozoic eras to form the African continent. It consists of two Archean centers juxtaposed against multiple Paleoproterozoic domains made of greenstone belts, sedimentary basins, regional granitoid-tonalite-trondhjemite-granodiorite (TTG) plutons, and large shear zones. The craton is overlain by Neoproterozoic and younger sedimentary basins. The boundaries of the WAC are predominantly defined by a combination of geophysics and surface geology, with additional constraints by the geochemistry of the region. At one time, volcanic action around the rim of the craton may have contributed to a major global warming event.

<span class="mw-page-title-main">Volcanism of Eastern Canada</span>

The volcanism of Eastern Canada includes the hundreds of volcanic areas and extensive lava formations in Eastern Canada. The region's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Eastern Canada has very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Eastern Canada are Archean age greenstone belts containing a rare volcanic rock called komatiite.

The Rove Formation is a sedimentary rock formation of Middle Precambrian age underlying the upper northeastern part of Cook County, Minnesota, United States, and extending into Ontario, Canada. It is the youngest of the many layers of sedimentary rocks which constitute the Animikie Group.

<span class="mw-page-title-main">Algoman orogeny</span> Late Archaean episode of mountain building in what is now North America

The Algoman orogeny, known as the Kenoran orogeny in Canada, was an episode of mountain-building (orogeny) during the Late Archean Eon that involved repeated episodes of continental collisions, compressions and subductions. The Superior province and the Minnesota River Valley terrane collided about 2,700 to 2,500 million years ago. The collision folded the Earth's crust and produced enough heat and pressure to metamorphose the rock. Blocks were added to the Superior province along a 1,200 km (750 mi) boundary that stretches from present-day eastern South Dakota into the Lake Huron area. The Algoman orogeny brought the Archean Eon to a close, about 2,500 million years ago; it lasted less than 100 million years and marks a major change in the development of the Earth's crust.

The geology of Central African Republic (CAR) is part of the broader geology of Africa. CAR occupies a swath of ancient rocks, dating back billions of years that record significant aspects of Earth history and yield minerals vital to the country's small economy.

<span class="mw-page-title-main">Geology of Ontario</span>

The geology of Ontario is the study of rock formations in the most populated province in Canada- it is home to some of the oldest rock on Earth. The geology in Ontario consists of ancient Precambrian igneous and metamorphic rock which sits under younger, sedimentary rocks and soils.

The geology of Liberia is largely extremely ancient rock formed between 3.5 billion and 539 million years ago in the Archean and the Neoproterozoic, with some rocks from the past 145 million years near the coast. The country has rich iron resources as well as some diamonds, gold and other minerals in ancient sediment formations weathered to higher concentrations by tropical rainfall.

The geology of Mozambique is primarily extremely old Precambrian metamorphic and igneous crystalline basement rock, formed in the Archean and Proterozoic, in some cases more than two billion years ago. Mozambique contains greenstone belts and spans the Zimbabwe Craton, a section of ancient stable crust. The region was impacted by major tectonic events, such as the mountain building Irumide orogeny, Pan-African orogeny and the Snowball Earth glaciation. Large basins that formed in the last half-billion years have filled with extensive continental and marine sedimentary rocks, including rocks of the extensive Karoo Supergroup which exist across Southern Africa. In some cases these units are capped by volcanic rocks. As a result of its complex and ancient geology, Mozambique has deposits of iron, coal, gold, mineral sands, bauxite, copper and other natural resources.

The geology of the Northwest Territories has been mapped in different quadrangles by the Canadian government. The region has some of the oldest rocks in the world and among the oldest in North America, formed from several sections of stable craton continental crust, including the Slave Craton, Rae Craton and Hearne Craton. These rocks form the Archean and Proterozoic Precambrian basement rock of the region and are the subject of extensive research to understand continental crust and tectonic conditions on the early Earth.

The Superior Craton is a stable crustal block covering Quebec, Ontario, and southeast Manitoba in Canada, and northern Minnesota in the United States. It is the biggest craton among those formed during the Archean period. A craton is a large part of the Earth's crust that has been stable and subjected to very little geological changes over a long time. The size of Superior Craton is about 1,572,000 km2. The craton underwent a series of events from 4.3 to 2.57 Ga. These events included the growth, drifting and deformation of both oceanic and continental crusts.

References

  1. 1 2 The Atlas of Canada (12 September 2016). "Physiographic Regions Map". Natural Resources Canada. Retrieved 2019-11-15.
  2. 1 2 "Canadian Shield". Encyclopædia Britannica . Archived from the original on 2015-06-24. Retrieved 2009-02-10.
  3. ↑ Marshak, Stephen (2009). Essentials of geology (3rd ed.). New York: W.W. Norton. ISBN   978-0393932386.
  4. ↑ Alexander Murray; Harrisson Panabaker; Holy O'Rourke; David Barrett (7 February 2006). "Canadian Shield". The Canadian Encyclopedia. Retrieved 29 May 2024. Formed over 3 billion years through processes such as plate tectonics, erosion and glaciation
  5. ↑ Corrigan, D. (2008). "Metallogeny and Tectonic Evolution of the Trans-Hudson Orogen" (PDF). Archived from the original (PDF) on April 9, 2008. Retrieved 2008-03-05.
  6. ↑ Peterson Field Guide to Geology of Eastern North America by Roberts, David & Roger Tory Peterson.
  7. ↑ Alberta Heritage - Alberta Online Encyclopedia Archived 2010-12-08 at Archive-It - The Canadian Shield Region of Alberta
  8. ↑ Tsuyoshi Iizuka, at al., "Geology and Zircon Geochronology of the Acasta Gneiss Complex", Precambrian Research, 153 (2007) pp. 179–208
  9. ↑ Pidwirny, M. (2006). "The Drainage Basin Concept". Fundamentals of Physical Geography (2nd ed.).
  10. ↑ Clark, Bruce W. (1999). "Geologic History" . Making Connections: Canada's geography. Scarborough, Ontario: Prentice Hall Ginn Canada. pp.  95. ISBN   978-0-13-012635-1.
  11. ↑ Ambrose, J. W. (1 September 1964). "Exhumed paleoplains of the Precambrian Shield of North America". American Journal of Science. 262 (7): 817–857. Bibcode:1964AmJS..262..817A. doi: 10.2475/ajs.262.7.817 .
  12. ↑ Shilts, William W.; Aylsworth, Janice M.; Kaszycki, Christine A.; Klassen, Rodney A. (1987). "Canadian Shield". Geomorphic Systems of North America: 119–161. doi:10.1130/DNAG-CENT-v2.119. ISBN   0813753023.
  13. ↑ Card, K.D. (August 1990). "A review of the Superior Province of the Canadian Shield, a product of Archean accretion". Precambrian Research. 48 (1–2): 99–156. Bibcode:1990PreR...48...99C. doi:10.1016/0301-9268(90)90059-Y.
  14. ↑ Smithies, R.H (15 October 2000). "The Archaean tonalite–trondhjemite–granodiorite (TTG) series is not an analogue of Cenozoic adakite". Earth and Planetary Science Letters. 182 (1): 115–125. Bibcode:2000E&PSL.182..115S. doi:10.1016/S0012-821X(00)00236-3.
  15. ↑ de Geoffroy, J.; Wignall, T. K. (1 May 1971). "A probabilistic appraisal of mineral resources in a portion of the Grenville Province of the Canadian shield". Economic Geology. 66 (3): 466–479. Bibcode:1971EcGeo..66..466D. doi:10.2113/gsecongeo.66.3.466.
  16. ↑ Caldera Volcanoes Archived 2012-08-14 at the Wayback Machine Retrieved on 2007-07-20
  17. ↑ Pilkington, Mark; Roest, Walter R. (1998). "Removing varying directional trends in aeromagnetic data". Geophysics. 63 (2): 446–453. Bibcode:1998Geop...63..446P. doi:10.1190/1.1444345.
  18. ↑ "Barbeau Peak". Bivouac.com.
  19. ↑ World Wildlife Fund, ed. (2001). "Northern Canadian Shield taiga". WildWorld Ecoregion Profile. National Geographic Society. Archived from the original on 2010-03-08.
  20. ↑ C. Michael Hogan (2008) Polar Bear: Ursus maritimus, Globaltwitcher.com, ed. Nicklas Stromberg Archived December 24, 2008, at the Wayback Machine
  21. ↑ "Making Sense of Shield Lakes and Rivers | Northern Ontario Travel". 28 June 2016.
  22. ↑ "Wildlife of the Boreal Shield Ecozone".
  23. ↑ 3-D Magnetic Imaging using Conjugate Gradients: Temagami anomaly Archived 2009-07-11 at the Wayback Machine Retrieved on 2008-03-12
  24. ↑ Troymet Exploration, Report on the 2007 Diamond Drilling Program, McClarty Lake Project, Manitoba: The Pas Mining District NTS 63-K-08; UTM ZONE 14 N 415938 E, 6038968 N; 54° 29′ 28″ N 100° 17′ 52″ W , by Jessica Norris & Tracy Hurley (Whitehorse, Yukon: Aurora Geosciences, 2007‑09‑24).

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.