Understanding The Canadian Shield

It’s Geology; It’s Ecology:

The Canadian Shield, also known as the Precambrian Shield or Laurentian Plateau, covers about half of Canada as well as most of Greenland and part of the northern United States; an area of 4.4 million square kilometers (1.7 million square miles).It is the oldest part of the North American crustal plate and contains fossils of bacteria and algae over 2 billion years old. The shield is composed of granite and the earth’s greatest area of exposed Precambrian rock (igneous and metamorphic rock formed in the Precambrian geological era 500 million years ago).

The shield was the first part of the continent to be permanently raised above sea level. Subsequent rising and falling, folding, erosion and continental ice sheets have created its present topography. The reoccurring invasion and withdrawal of the ice sheets (1.6 million to 10,000 years ago) depressed the surface creating Hudson Bay, scraped out tens of thousands of lake basins, carried away much of the soil cover and redeposited glacial debris.

The shield plateau ranges from 305 to 610 meters (1000 to 2000 feet) above sea level. In northern Labrador and Baffin Island the crustal plate has tilted so much that it rises over 1,500 meters (5,000 feet) above sea level. There are a number of mountain ranges within the shield: the Adirondack (northeastern New York state), Superior Highlands (northern Minnesota, Wisconsin & Michigan states), Torngat and Laurentian.

The shield is a rich source of metallic minerals such as iron, nickel, copper, zinc, uranium, gold, silver, platinum and molybdenum.

Ecology:

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 ice age, which covered the Shield and scraped the rock clean.

The lowlands of the Canadian Shield have very dense soil that is not suitable for forestation, but it also contains many marshes and bogs. The rest of the region has coarse soil that does not retain moisture well and is frozen as permafrost year round. Forests are not as dense in the north.

The Shield is covered in parts by vast boreal forests in the south that support important natural ecosystems as well as a major logging industry. Hydrographical drainage is generally poor, the effects of glaciation being one of the many reasons. Tundra typically prevails in the northern regions. Many mammals such as caribou, wolverines, weasels, mink, otters, grizzlies, polar bears and black bears are present. In the case of polar bears (Ursus maritimus) the Shield area contains many of the denning locations such as the Wapusk National Park.

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 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.

In northeastern Quebec, the giant Manicouagan Reservoir is the site of an extensive hydroelectric project (Manic‐cinq, or Manic‐5). This is one of the largest‐known meteorite impact craters 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 tons of sulfide have been mined.

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 kilometers (93 mi) depth to the surface. Currently the Ekati and Diavik mines are actively mining kimberlite diamonds.

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