Canadian Shield
6230
225684409
2008-07-14T21:59:07Z
68.214.28.38
/* Mining and economics */
{{Refimprove|date=January 2008}}
[[Image:Canadianshield.gif|right|thumb|Canadian Shield]]
[[Image:Canadian Shield.jpg|right|thumb|Canadian Shield Landform.]]
The '''Canadian Shield''' — also called the '''Laurentian Plateau''', or '''Bouclier Canadien''' (French) — is a large [[shield (geology)|geological shield]] covered by a thin layer of soil that forms the nucleus of the [[North American craton|North American or Laurentia craton]]. It has a deep, common, joined [[bedrock]] region in eastern and central [[Canada]] and stretches North from the [[Great Lakes]] to the [[Arctic Ocean]], covering over half the country.
== Geographical extent ==
It also includes most of [[Greenland]]{{Clarifyme|date=May 2008}}<!--This does not agree with the map shown; either the text is wrong or the map must be replaced.--> and extends into the [[United States geology|United States]] as the [[Adirondack Mountains]] and 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 [[craton]] signifying 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 (unit)|Ga]], with the most substantial growth period occurring during the [[Trans-Hudson orogeny]], between ca. 1.90 to 1.80 Ga.<ref name=Corrigan>{{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]]}}</ref> 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 [[Archaean]] rock. The [[Metamorphic rock|metamorphic]] [[Rock (geology)|base rocks]] are mostly from the [[Precambrian]] [[Era (geology)|Era]] (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 [[monadnock]]s and low mountain ranges (including the [[Torngat Mountains|Torngat]] and [[Laurentian Mountains]]) probably eroded from the plateau during the [[Cenozoic]] era. During the [[Pleistocene]] epoch, 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 ==
[[Hydrography|Hydrographical]] drainage is generally poor, the effects of [[glaciation]] being one of the reasons. The Canadian shield is covered by [[boreal forest]]s in the south, while [[tundra]] prevails in the northern regions. Population is scarce, and industrial development is minimal<ref>[http://www.bartleby.com/65/ca/CanadSh.html Canadian Shield] - Columbia Encyclopedia, Sixth Edition, 2005</ref>, however the region has a large water-power potential and is a source of [[ore]] and [[timber]]. Many mammals such as [[caribou]], [[wolverine]]s, [[weasel]]s, [[mink]], [[otter]]s, [[grizzly bear|grizzlies]] and [[American black bear|black bear]]s are also present in this area<ref>[http://www.nationalgeographic.com/wildworld/profiles/terrestrial/na/na0612.html National Geographic] - Northern Canadian Shield taiga</ref>.
==Regional extent==
When the [[Greenland]] section is included, the 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, [[Labrador]], most of [[Quebec]] north of the [[Saint Lawrence River|St. Lawrence River]], much of [[Ontario]] including northern sections of the southern peninsula between the [[Great Lakes]], the [[Adirondack Mountains]]<ref>Peterson Field Guide to Geology of Eastern North America by Roberts, David & Roger Tory Peterson.</ref> of northern [[New York]], the northernmost part of Lower [[Michigan]] and all of [[Upper Michigan]], northern [[Wisconsin]], and northeastern [[Minnesota]], the central/northern portions of [[Manitoba]] away from Hudson Bay and the [[Great Plains]], northern [[Saskatchewan]], a small portion of northeastern [[Alberta]],<ref>[http://www.abheritage.ca/abnature/shield/shield.htm Alberta Heritage - Alberta Online Encyclopedia] - The Canadian Shield Region of Alberta</ref> and the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border ([[Northwest Territories]] and [[Nunavut]])<ref>[http://www.britannica.com/eb/article-9019922 Encyclopædia Britannica] - Canadian Shield</ref>. In total it covers approximately 8 million square kilometers. It covers even more area and stretches to the Western Cordillera in the west and [[Appalachian Mountains|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<!---, but by some definitions these submerged regions may not ''technically'' be part of the Shield since they are not on the surfaces --->.
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 doesn't hold moisture very well and is frozen all year round. Forests are less dense in the north.
==Physiography==
The Canadian shield is a [[Physiographic regions of the world|physiographic division]], consisting of 5 smaller physiographic provinces, the [[Laurentian Upland]], Kazan, Davis, Hudson, and James.<ref>{{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 }}</ref>
==Geology==
[[Image:North america craton nps.gif|thumb|Canadian Shield is exposed part of [[North American craton]] or ''[[Laurentia]]''.]]
The current [[geomorphology|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 [[glacier|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 [[drainage basin|watershed]]s 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 [[mountain]]s (about 12,000 meters)<ref>
{{cite book
|last=Clark
|first=Bruce W.
|chapter=Geologic History|pages=pp. 95
|title=Making Connections: Canada's geography
|year=1999
|edition=
|publisher=Prentice Hall Ginn Canada
|location=Scarborough, Ontario
|id=ISBN 0-13-012635-7}}</ref> with much [[volcanic]] activity, but over the millennia the area was eroded to its current [[topography|topographic]] appearance of relatively low relief. It contains some of the most ancient volcanoes on Earth. It has over 150 [[volcanic belt]]s (now deformed and eroded down to nearly flat [[plain]]s) 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.
The [[Sturgeon Lake Caldera]] in [[Kenora District, Ontario]] is one of the world's best preserved [[mineralization (geology)|mineralized]] [[Neoarchean]] [[caldera]] complexes, which is some 2.7 billion years old.<ref>[http://www.d.umn.edu/~rmorton/ronshome/Volcanoes/calderas.html Caldera Volcanoes] Retrieved on [[2007-07-20]] </ref> The Canadian Shield also contains the [[Mackenzie dike swarm]], which is the largest [[dike swarm]] known on [[Earth]].<ref>[http://gdcinfo.agg.nrcan.gc.ca/app/dyke/index_e.html Supressing Varying Directional Trends] Retrieved on [[2007-07-28]]</ref>
[[Image:Canadian Shield Ontario.jpg|thumb|200px|left|Typical Canadian Shield: pines, lakes, bogs, and rock.]]
Mountains have deep roots and float on the denser [[Mantle (geology)|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 (geology)|mineralization]]. Although these mountains are now heavily eroded, many large mountains still exist in Canada's far north called the [[Arctic Cordillera]].
This a vast deeply dissected [[mountain range]], streching from northernmost [[Ellesmere Island]] to the northernmost tip of [[Labrador]]. The range's highest peak is [[Nunavut]]'s [[Barbeau Peak]] at 2,616 meters (8,583 feet) above [[sea level]].<ref>[http://www.bivouac.com/MtnPg.asp?MtnId=261 Barbeau Peak] in the Canadian Mountain Encyclopedia. Retrieved on [[2007-11-10]]</ref> [[Precambrian]] rock is the major component of the [[bedrock]].
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 billion years ago, during the [[Neoarchean]] era. It was split into Greenland, Laurentia, [[Scotland]], [[Siberia]], [[East Antarctica]] and is now roughly situated in the [[Arctic]] around the current [[North Pole]].
==Mining and economics==
The Shield is one of the world's richest area in terms of [[mineral]] [[ore]]s. 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 [[Greater Sudbury|Sudbury]], [[Ontario]]. Sudbury is an exception to the normal process of forming minerals in the Shield since there is significant evidence that the [[Sudbury Basin]] is an ancient [[meteorite]] [[impact crater]]. 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.<ref name="GH">[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]]</ref>
In northeastern Quebec, the giant [[Manicouagan Reservoir]] is the site of a massive hydroeletric project (Manic-cinq, or Manic-5). This is one of the largest-known [[meteor]] [[impact crater]]s on Earth.
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.<ref name=Norris>{{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=[[PDF]] |accessdate=2008-02-22 }}</ref>
The Shield, particularly 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 [[lithosphere|lithospheric]] [[Mantle (geology)|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 Diamond Mine|Ekati]] and [[Diavik Diamond Mine|Diavik]] mines are actively mining kimberlite diamonds.
The Shield is also covered by vast [[boreal forest]]s that support an important [[logging]] industry.
==References==
<div class="references-small"><references/>
</div>
==See also==
*[[Glacial history of Minnesota]]
*[[Shield (geology)|Shield]]
*[[Craton]]
*[[Platform (geology)|Platform]]
*[[Oldest rock]]
*[[basement (geology)|Basement]]
*[[Continental platform|Platform basement]]
*[[Volcanism in Canada]]
{{Canada topics}}
{{Geography topics}}
{{Physical geography topics}}
[[Category:Cratons]]
[[Category:Plate tectonics]]
[[Category:Geology of Canada]]
[[Category:Geography of Ontario]]
[[Category:Geology of Michigan]]
[[Category:Geology of Minnesota]]
[[Category:Geology of New York]]
[[Category:Geology of Wisconsin]]
[[Category:Geology of Greenland]]
[[Category:Physiographic divisions]]
[[Category:Regional geology]]
[[Category:Stratigraphy of Canada]]
[[af:Kanadese Skild]]
[[cs:Kanadský štít]]
[[de:Kanadischer Schild]]
[[es:Escudo Canadiense]]
[[eo:Laŭrenca tabulo]]
[[fr:Bouclier canadien]]
[[gl:Escudo Canadense]]
[[it:Scudo canadese]]
[[lt:Kanados skydas]]
[[nl:Canadees Schild]]
[[ja:カナダ楯状地]]
[[no:Grunnfjellsskjoldet]]
[[pl:Tarcza Kanadyjska]]
[[pt:Escudo Canadiano]]
[[ru:Канадский щит]]
[[fi:Kanadan kilpi]]
[[sv:Kanadensiska skölden]]
[[uk:Канадський щит]]