Difference between revisions of "Canadian Shield" - New World Encyclopedia
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[[Image:Canadianshield.gif|right|thumb|Canadian Shield]] | [[Image:Canadianshield.gif|right|thumb|Canadian Shield]] | ||
| − | The '''Canadian Shield'''—also called the '''Laurentian Plateau''', '''Laurentian Shield''', Bouclier Canadien (French), or '''Precambrian Shield'''— is a massive U-shaped, almost circular region of the Earth that has extensive exposed [[Precambrium]] rock, forms the nucleus of [[North America]], and extends from Lake Superior on the south to the Arctic Islands on the north, and from western [[Canada]] eastward across to most of [[Greenland]], including also the Adirondack Mountains and the Northern Highlands | + | The '''Canadian Shield'''—also called the '''Laurentian Plateau''', '''Laurentian Shield''', Bouclier Canadien (French), or '''Precambrian Shield'''— is a massive U-shaped, almost circular region of the Earth that has extensive exposed [[Precambrium]] rock, forms the nucleus of [[North America]], and extends from Lake Superior on the south to the Arctic Islands on the north, and from western [[Canada]] eastward across to most of [[Greenland]], including also the Adirondack Mountains in northeastern United States and the Northern Highlands in Wisconsin in the United States. |
In geology, a '''shield'' is generally a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas, and that normally form the nucleus of continents. Most often they are bordered by belts of folded [[Cambrian]] rocks. The Canadian shield forms the nucleus of North America and is covered by a thin layer of [[soil]] that forms the nucleus of the [[North American craton]]— an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for over 500 million years. | In geology, a '''shield'' is generally a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas, and that normally form the nucleus of continents. Most often they are bordered by belts of folded [[Cambrian]] rocks. The Canadian shield forms the nucleus of North America and is covered by a thin layer of [[soil]] that forms the nucleus of the [[North American craton]]— an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for over 500 million years. | ||
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==Overview== | ==Overview== | ||
| − | + | 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, and nearly half of Canada's total area, including Labrador, most of [[Quebec]] north of the [[Saint Lawrence River|St. Lawrence River]], and much of [[Ontario]], including northern sections of the southern peninsula between the [[Great Lakes]]. It also includes in Canada the central/northern portions of [[Manitoba]] away from Hudson Bay and the [[Great Plains]], northern [[Saskatchewan]], and a small portion of northeastern [[Alberta]], as well as plunges under the mountains and plains to form a foundation under the province (HCF 2007). It also includes the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border (Northwest Territories and Nunavut). In the United States, the Canadian Shield includes the [[Adirondack Mountains]] of northern [[New York]], the northernmost part of Lower [[Michigan]] and all of [[Upper Michigan]], northern [[Wisconsin]], and northeastern [[Minnesota]]. | |
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| + | In total it covers approximately 8 million square kilometers. It covers even more area and stretches till the Western Cordillera in the west and Appalachians in the east but the formations remain underground. For example, in Alberta: as well as plunges under the mountains and plains to form a foundation under the province (HCF 2007). | ||
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| + | 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 --->. | ||
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| + | 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. | ||
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 (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/305–610 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. | 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 (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/305–610 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. | ||
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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>. | 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>. | ||
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==Geology== | ==Geology== | ||
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==References== | ==References== | ||
<div class="references-small"><references/> | <div class="references-small"><references/> | ||
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| + | Heritage Community Foundation (HCF). 2007. [http://www.abheritage.ca/abnature/shield/shield.htm The Canadian Shield Region]. ''Alberta Online Encyclopedia''. | ||
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</div> | </div> | ||
Revision as of 21:51, 12 May 2007
The Canadian Shield—also called the Laurentian Plateau, Laurentian Shield, Bouclier Canadien (French), or Precambrian Shield— is a massive U-shaped, almost circular region of the Earth that has extensive exposed Precambrium rock, forms the nucleus of North America, and extends from Lake Superior on the south to the Arctic Islands on the north, and from western Canada eastward across to most of Greenland, including also the Adirondack Mountains in northeastern United States and the Northern Highlands in Wisconsin in the United States.
In geology, a 'shield is generally a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas, and that normally form the nucleus of continents. Most often they are bordered by belts of folded Cambrian rocks. The Canadian shield forms the nucleus of North America and is covered by a thin layer of soil that forms the nucleus of the North American craton— an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for over 500 million years.
Viewed from space, the Canadian Shield gives the appearance of a warrior's shield or a giant horseshoe. It is a subsection of the Laurentia craton signifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils.
Overview
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, and nearly half of Canada's total area, including Labrador, most of Quebec north of the St. Lawrence River, and much of Ontario, including northern sections of the southern peninsula between the Great Lakes. It also includes in Canada the central/northern portions of Manitoba away from Hudson Bay and the Great Plains, northern Saskatchewan, and a small portion of northeastern Alberta, as well as plunges under the mountains and plains to form a foundation under the province (HCF 2007). It also includes the mainland northern Canadian territories to the east of a line extended north from the Saskatchewan/Alberta border (Northwest Territories and Nunavut). In the United States, the Canadian Shield includes the Adirondack Mountains of northern New York, the northernmost part of Lower Michigan and all of Upper Michigan, northern Wisconsin, and northeastern Minnesota.
In total it covers approximately 8 million square kilometers. It covers even more area and stretches till the Western Cordillera in the west and Appalachians in the east but the formations remain underground. For example, in Alberta: as well as plunges under the mountains and plains to form a foundation under the province (HCF 2007).
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 doesn't hold moisture very well and is frozen all year round. Forests are less dense in the north.
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 base rocks are mostly from the Precambrian 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/305–610 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 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.
Hydrographical drainage is generally poor, the effects of glaciation being one of the reasons. The Canadian shield is covered by boreal forests in the south, while tundra prevails in the northern regions. Population is scarce, and industrial development is generally poor[1], however the region has a large water-power potential and is a source of ore and timber.
Many mammals such as caribou, wolverines, weasels, mink, otters, grizzlies and black bears are also present in this area[2].
Geology
Such a large area of exposed old rock is unusual. 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 that were about 12,000 m[citation needed] in height and much volcanic activity, 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.
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.
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, Laurasia, 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 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 Greater 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 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 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 logging industry.
ReferencesISBN links support NWE through referral fees
- ↑ Canadian Shield - Columbia Encyclopedia, Sixth Edition, 2005
- ↑ National Geographic - Northern Canadian Shield taiga
Heritage Community Foundation (HCF). 2007. The Canadian Shield Region. Alberta Online Encyclopedia.
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