The Canadian Shield, also called the Laurentian Plateau, or
Bouclier canadien (French), is a massive geological shield covered
by a thin layer of soil that forms the nucleus of the North
American or Laurentia craton. It is an area mostly composed of
igneous rock which relates to its long volcanic history. 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 over half of Canada; it also extends south into the
northern reaches of the United States. Population is scarce, and
industrial development is minimal, although the region has a large
hydroelectric power potential.
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 ft) with much volcanic activity, but
over the millennia the area was eroded to its current topographic
appearance of relatively low relief. It has some of the oldest
volcanoes on the planet. 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. 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.
In order to gain credit for this Earth Cache please email me the
answers to the following questions:
- What is your elevation at ground zero?
- Describe the exposed rock in the area: color, shape
texture.
- What kinds of evidence did you see on your journey to ground
zero of the laurentian shield?
- It is optional for you to post a photo of you and your
group.
