Geology
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 (about 12,000 metres or 39,000 feet) with much volcanic activity, but over hundreds of million of years, the area has been eroded to its current topographic appearance of relatively low relief. It has some of the oldest (extinct) volcanoes on the planet. It has over 150 volcanic belts (now deformed and eroded down to nearly flat plains) whose bedrock ranges 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 reach 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 mineralized Neoarchean caldera complexes, which is some 2.7 billion years old. The Canadian Shield also contains the Mackenzie dike swarm, which is the largest dike swarm known on Earth.
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. Although these mountains are now heavily eroded, many large mountains still exist in Canada's far north called the Arctic Cordillera. This is a vast deeply dissected mountain range, stretching from northernmost Ellesmere Island to the northernmost tip of Labrador. The range's highest peak is Nunavut's Barbeau Peak at 2,616 metres (8,583 ft) above sea level. 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.
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