- Canadian Shield
The Canadian Shield — also called the Laurentian Plateau, or Bouclier Canadien (French) — is a large geological shield covered by a thin layer of soil that forms the nucleus of the North American or Laurentia craton. It has a deep, common, joined
bedrockregion in eastern and central Canadaand stretches North from the Great Lakesto the Arctic Ocean, covering over half the country.
It also includes most of
GreenlandClarifyme|date=May 2008 and extends into the United States as the Adirondack Mountainsand the Northern Highland. The Canadian Shield is U-shaped, but almost circular, which gives it an appearance of a warrior's shield or a giant horseshoe, and is a subsection of the Laurentia cratonsignifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils.
The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of Proterozoic age that were progressively amalgamated during the interval 2.45 to 1.24 Ga, with the most substantial growth period occurring during the
Trans-Hudson orogeny, between ca. 1.90 to 1.80 Ga.cite journal |author=Corrigan, D. |year=2008 |title=Metallogeny and Tectonic Evolution of the Trans-Hudson Orogen |url=http://www.pdac.ca/pdac/conv/2008/pdf-tech-session/ts-corrigan.pdf | Retrieved on 2008-03-05] 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 Archaeanrock. The metamorphic base rocks are mostly from the PrecambrianEra (between 4.5 billion and 540 million years ago), and have been repeatedly uplifted and eroded. Today it consists largely of an area of low relief (1,000–2,000 ft/300–600 m above sea level) with a few monadnocks and low mountain ranges (including the Torngat and Laurentian Mountains) probably eroded from the plateau during the Cenozoicera. During the Pleistoceneepoch, continental ice sheets depressed the land surface (see Hudson Bay), scooped out thousands of lake basins, and carried away much of the region's soil.
Recent glaciation effects
Hydrographical drainage is generally poor, the effects of
glaciationbeing one of the many reasons. The Canadian shield is covered by boreal forestin the south, while tundraprevails in the northern regions. Population is scarce, and industrial development is minimal, [ [http://www.bartleby.com/65/ca/CanadSh.html Canadian Shield] - Columbia Encyclopedia, Sixth Edition, 2005] however the region has a large water-power potential, and is a source of oreand timber. Many mammals such as caribou, wolverines, weasels, mink, otters, grizzlies and black bears are present. [ [http://www.nationalgeographic.com/wildworld/profiles/terrestrial/na/na0612.html National Geographic] - Northern Canadian Shield taiga]
Greenlandsection is included, the Shield is approximately circular bounded on the northeast by the northeast edge of Greenland, with Hudson Bayin the middle. It covers much of Greenland, Labrador, most of Quebecnorth of the St. Lawrence River, much of Ontarioincluding northern sections of the southern peninsula between the Great Lakes, the Adirondack Mountains[Peterson Field Guide to Geology of Eastern North America by Roberts, David & Roger Tory Peterson.] of northern New York, the northernmost part of Lower Michiganand all of Upper Michigan, northern Wisconsin, and northeastern Minnesota, the central/northern portions of Manitobaaway from Hudson Bay and the Great Plains, northern Saskatchewan, a small portion of northeastern Alberta, [ [http://www.abheritage.ca/abnature/shield/shield.htm Alberta Heritage - Alberta Online Encyclopedia] - The Canadian Shield Region of Alberta] and the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border ( Northwest Territoriesand Nunavut). [ [http://www.britannica.com/eb/article-9019922 Encyclopædia Britannica] - Canadian Shield] In total it covers approximately 8 million square kilometers. It covers even more area and stretches to the Western Cordillera in the west and Appalachians in the east but the formations are still underground.
The underlying rock structure does include Hudson Bay and the submerged area between North America and Greenland .
The Canadian shield is so large the climate varies across it. In the southern parts the climate is seasonal; the average temperature in the winter is -18 degrees Celsius, and in the summer it is 25 degrees Celsius. The growing season of about 120 days coincides with summer daylight averaging about 15 hours, while winter daylight averages about 8.5 hours. In the northern parts it is very cold. The average temperatures range from 15 degrees Celsius in the summer to -35 degrees Celsius in winter. The growing season is only 60 days. Winter daylight hours are about 5.5 hours, and in the summer the daylight hours are about 18.5 hours. The lowlands of the Canadian shield have soggy soil suitable for planting trees, but it contains many marshes and bogs. The rest of the region has coarse soil that does not hold moisture very well and is frozen all year round. Forests are less dense in the north.
The Canadian shield is a physiographic division, consisting of 5 smaller physiographic provinces, the
Laurentian Upland, Kazan, Davis, Hudson, and James. [cite web |last=|first=| authorlink = | coauthors = |title=The Atlas of Canada |publisher=Natural Resources Canada |date=|url=http://atlas.nrcan.gc.ca/sites/english/maps/reference/anniversary_maps/physiographicregions/map.pdf |accessdate=2007-12-27 ]
North American cratonor " Laurentia".]
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 last ice age, which covered the Shield and scraped the rock clean.
The multitude of rivers and lakes in the entire region is caused by the watersheds of the area being so young and in a state of sorting themselves out with the added effect of
post-glacial rebound. The Shield was originally an area of very large mountains (about 12,000 meters) [cite book
chapter=Geologic History|pages=pp. 95
title=Making Connections: Canada's geography
publisher=Prentice Hall Ginn Canada
id=ISBN 0-13-012635-7] with much
volcanicactivity, but over the millennia the area was eroded to its current topographic appearance of relatively low relief. It contains some of the most ancient volcanoes on Earth. It has over 150 volcanic belts (now deformed and eroded down to nearly flat plains) that range from 600 to 1200 million years old.
Each belt probably grew by the coalescence of accumulations erupted from numerous vents, making the tally of volcanoes in the hundreds. Many of Canada's major ore deposits are associated with Precambrian volcanoes.
Sturgeon Lake Calderain Kenora District, Ontariois one of the world's best preserved mineralized Neoarchean calderacomplexes, which is some 2.7 billion years old. [ [http://www.d.umn.edu/~rmorton/ronshome/Volcanoes/calderas.html Caldera Volcanoes] Retrieved on 2007-07-20] The Canadian Shield also contains the Mackenzie dike swarm, which is the largest dike swarmknown on Earth. [ [http://gdcinfo.agg.nrcan.gc.ca/app/dyke/index_e.html Supressing Varying Directional Trends] Retrieved on 2007-07-28]
Mountains have deep roots and float on the denser mantle much like an
icebergat 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
This is a vast deeply dissected
mountain range, stretching from northernmost Ellesmere Islandto the northernmost tip of Labrador. The range's highest peak is Nunavut's Barbeau Peakat 2,616 meters (8,583 feet) above sea level. [ [http://www.bivouac.com/MtnPg.asp?MtnId=261 Barbeau Peak] in the Canadian Mountain Encyclopedia. Retrieved on 2007-11-10] Precambrianrock is the major component of the bedrock.
North American cratonis 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 billion years ago, during the Neoarcheanera. It was split into Greenland, Laurentia, Scotland, Siberia, East Antarcticaand is now roughly situated in the Arcticaround the current North Pole.
Mining and economics
The 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. Throughout the Shield 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 there is significant evidence that the Sudbury Basinis an ancient meteorite impact crater. The nearby, but less known Temagami Magnetic Anomalyhas striking similarities to the Sudbury Basin. This suggests it could be a second metal-rich impact crater. [http://gdcinfo.agg.nrcan.gc.ca/app/3Dimaging/temagami_e.html 3-D Magnetic Imaging using Conjugate Gradients: Temagami anomaly] Retrieved on 2008-03-12]
In northeastern Quebec, the giant
Manicouagan Reservoiris the site of a massive hydroeletric project (Manic-cinq, or Manic-5). This is one of the largest-known meteor impact craters on Earth.
Flin Flon greenstone beltin central Manitobaand east-central Saskatchewanis one of the largest Paleoproterozoicvolcanic-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.cite paper |author=Norris, Jessica |title=Report on the 2007 Diamond Drilling Program McClarty Lake Project, Manitoba |publisher=Aurora Geosciences Ltd. |date=2007 |url=http://www.troymet.com/i/pdf/2007McClarty43-101.pdf |format=
The Shield, particularly the portion in the
Northwest Territories, has recently been the site of several major diamonddiscoveries. The kimberlitepipes 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 km depth to the surface. Currently the Ekati and Diavik mines are actively mining kimberlite diamonds.
The Shield is also covered by vast
boreal forests that support an important loggingindustry.
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