Difference between revisions of "Canadian Shield" - New World Encyclopedia
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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. | 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. | ||
| − | == | + | ==Location== |
| − | 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 | + | 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]] (HCF 2007), as well as 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 | + | In total, the Canadian Shield covers approximately 8 million square kilometers. If underground areas are included, the the Canadian Shield covers even more area. For example, in Alberta, Canada it plunges under the mountains and plains to form a foundation under the province (HCF 2007), and it also stretches till the Western Cordillera in the west and Appalachians in the east, but the formations remain underground. The underlying rock structure also include Hudson Bay and the submerged area between North America and Greenland, but by some definitions these submerged regions are not ''technically'' part of the Shield since they are not on the surface. |
| − | + | ==Climate and ecology== | |
| − | The Canadian shield is so large the climate varies across it | + | The Canadian shield is so large that the climate varies across it. |
| − | + | [[Image:Canadian Shield Ontario.jpg|thumb|200px|left|Typical Canadian Shield: pines, lakes, bogs, and rock.]] | |
| + | 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, the climate 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 in duration. Winter daylight hours are about 5.5 hours, and in the summer the daylight hours are about 18.5 hours. | |
| − | + | [[Hydrography|Hydrographical]] drainage is generally poor, the effects of [[glaciation]] being one of the reasons. 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. | |
| + | The Canadian shield is covered by [[boreal forest]]s in the south. Forests are less dense in the north, and tundra prevails in the more northern regions. Transitional between the tundra and the boreal forests is the Northern Canadian Shield Taiga ecoregion, characterized by low-lying bushes because of the increasingly severe weather and unsuitable soil conditions (WWF 2001). The human population tends to be scarce the taiga, but many mammals are present in the area, such as [[caribou]], [[wolverine]]s, [[weasel]]s, [[mink]], [[otter]]s, [[grizzly bear|grizzlies]], and [[American black bear|black bear]]s. | ||
==Geology== | ==Geology== | ||
[[Image:North america craton nps.gif|thumb|Canadian Shield is exposed part of [[North American craton]] or ''[[Laurentia]]''.]] | [[Image:North america craton nps.gif|thumb|Canadian Shield is exposed part of [[North American craton]] or ''[[Laurentia]]''.]] | ||
| − | |||
| − | [[ | + | The exposed metamorphic rock of the Canadian shield mostly trace to the [[Precambrian]] era, between 4.5 billion and 542 million years ago, including extensive exposed rock from the [[Archaean]] eon. The Archean is set at the time period beginning with the formation of the earth's crust and the oldest earth rocks 3.8-3.96 billion years ago (3960-3800 million years ago) and extending to the [[Proterozoic]], 2.5 billion years ago (2500 mya). The [[origin of life]] traces to the Archean, with [[prokaryote]] [[fossil]]s known from 3.5 billion years ago. During the Archean, processes were also set in motion that prepared the foundation for multicellular life, with the development of an [[oxygen]] atmosphere and, it is speculated, possibly the appearance of the first [[eukaryote]]s around 2.7 billion years ago, near the end of the Archean (Mayr 2001). |
| + | |||
| + | Such a large area of exposed old rock as seen in the Canadian Shield is unusual. 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 that were about 12,000 m{{Fact|date=February 2007}} in height and 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 belts (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. | ||
| + | |||
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]]. | 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]]. | ||
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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]]. | 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]]. | ||
| + | |||
| + | |||
| + | 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. | ||
| + | |||
| + | 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. | ||
| + | |||
| + | |||
| + | |||
==Mining and economics== | ==Mining and economics== | ||
| + | Population is scarce, and industrial development is generally poor<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]]. | ||
| + | |||
| + | |||
The Shield is one of the world's richest areas 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, 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 is one of the world's richest areas 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, 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]]. | ||
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==References== | ==References== | ||
| − | |||
Heritage Community Foundation (HCF). 2007. [http://www.abheritage.ca/abnature/shield/shield.htm The Canadian Shield Region]. ''Alberta Online Encyclopedia''. | Heritage Community Foundation (HCF). 2007. [http://www.abheritage.ca/abnature/shield/shield.htm The Canadian Shield Region]. ''Alberta Online Encyclopedia''. | ||
| + | |||
| + | <ref>[http://www.nationalgeographic.com/wildworld/profiles/terrestrial/na/na0612.html National Geographic] - Northern Canadian Shield taiga</ref>. | ||
| + | |||
| + | WWF 2001. Northern Canadian Shield taiga (NA0612) | ||
| − | + | * Mayr, E. 2001. ''What Evolution Is''. New York, NY: Basic Books. ISBN 0465044263. | |
{{credit|Canadian_shield|129702989|Shield_(geology)|127322875|Craton_125469625}} | {{credit|Canadian_shield|129702989|Shield_(geology)|127322875|Craton_125469625}} | ||
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 22:49, 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.
Location
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 (HCF 2007), as well as 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, the Canadian Shield covers approximately 8 million square kilometers. If underground areas are included, the the Canadian Shield covers even more area. For example, in Alberta, Canada it plunges under the mountains and plains to form a foundation under the province (HCF 2007), and it also stretches till the Western Cordillera in the west and Appalachians in the east, but the formations remain underground. The underlying rock structure also include Hudson Bay and the submerged area between North America and Greenland, but by some definitions these submerged regions are not technically part of the Shield since they are not on the surface.
Climate and ecology
The Canadian shield is so large that 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, the climate 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 in duration. Winter daylight hours are about 5.5 hours, and in the summer the daylight hours are about 18.5 hours.
Hydrographical drainage is generally poor, the effects of glaciation being one of the reasons. 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.
The Canadian shield is covered by boreal forests in the south. Forests are less dense in the north, and tundra prevails in the more northern regions. Transitional between the tundra and the boreal forests is the Northern Canadian Shield Taiga ecoregion, characterized by low-lying bushes because of the increasingly severe weather and unsuitable soil conditions (WWF 2001). The human population tends to be scarce the taiga, but many mammals are present in the area, such as caribou, wolverines, weasels, mink, otters, grizzlies, and black bears.
Geology
The exposed metamorphic rock of the Canadian shield mostly trace to the Precambrian era, between 4.5 billion and 542 million years ago, including extensive exposed rock from the Archaean eon. The Archean is set at the time period beginning with the formation of the earth's crust and the oldest earth rocks 3.8-3.96 billion years ago (3960-3800 million years ago) and extending to the Proterozoic, 2.5 billion years ago (2500 mya). The origin of life traces to the Archean, with prokaryote fossils known from 3.5 billion years ago. During the Archean, processes were also set in motion that prepared the foundation for multicellular life, with the development of an oxygen atmosphere and, it is speculated, possibly the appearance of the first eukaryotes around 2.7 billion years ago, near the end of the Archean (Mayr 2001).
Such a large area of exposed old rock as seen in the Canadian Shield 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.
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.
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.
Mining and economics
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.
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
Heritage Community Foundation (HCF). 2007. The Canadian Shield Region. Alberta Online Encyclopedia.
[2].
WWF 2001. Northern Canadian Shield taiga (NA0612)
- Mayr, E. 2001. What Evolution Is. New York, NY: Basic Books. ISBN 0465044263.
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- ↑ Canadian Shield - Columbia Encyclopedia, Sixth Edition, 2005
- ↑ National Geographic - Northern Canadian Shield taiga
