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The Canadian Shield — also called the '''Precambrian Shield''', '''Laurentian Shield''', '''Laurentian Plateau''', or '''Bouclier Canadien''' (French) — is a large Shield covered by a thin layer of soil that forms the nucleus of the North American 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 half the country. It also includes most of Greenland and extends into the United States as the Adirondack Mountains and the Northern Highland . The Canadian Shield is U-shape, 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 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/300–600 m above sea level) with a few Monadnock s 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. and Timber . Many mammals such as Caribou , Wolverine s, Weasel s, Mink , Otter s, Grizzlies and Black Bear s are also present in this area National Geographic - Northern Canadian Shield taiga. REGIONAL EXTENT When the and Nunavut ) 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 doesn't hold moisture very well and is frozen all year round. Forests are less dense in the north. GEOLOGY or '' Laurentia ''.]] Such a large area of exposed old rock is unusual. The current 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, 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 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, 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 Forest s that support an important Logging industry. REFERENCES SEE ALSO |
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