The Canadian Shield, also called the Laurentian Plateau, or Bouclier
canadien (French), is a large area of exposed
Precambrian igneous and
high-grade metamorphic rocks (geological shield) that forms the
ancient geological core of the North American continent (the North
Craton or Laurentia). Composed of igneous rock resulting from
its long volcanic history, the area is covered by a thin layer of
soil. With a deep, common, joined bedrock region in eastern and
central Canada, it 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. Human population is sparse, and
industrial development is minimal, while mining is prevalent.
1 Geographical extent
4 Mining and economics
5 See also
7 Further reading
Canadian Shield is a physiographic division, consisting of five
smaller, physiographic provinces: the Laurentian Upland, Kazan Region,
Davis, Hudson and James. The shield extends into the United States
Adirondack Mountains (connected by the Frontenac Axis) and the
Superior Upland. The
Canadian Shield is U-shaped and is a subsection
Laurentia craton signifying the area of greatest glacial impact
(scraping down to bare rock) creating the thin soils. The Canadian
Shield is more than 3.96 billion years old. The
Canadian Shield once
had jagged peaks, higher than any of today's mountains, but millions
of years of erosion have changed these mountains to rolling hills.
Canadian Shield is a collage of
Archean plates and accreted
juvenile arc terranes and sedimentary basins of the
that were progressively amalgamated during the interval 2.45 to 1.24
Ga, with the most substantial growth period occurring during the
Trans-Hudson orogeny, between ca. 1.90 to 1.80 Ga. 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
Archean rock. The metamorphic base rocks are
mostly from the
Precambrian Supereon (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 300 to 610 m
(980 to 2,000 ft) 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.
Greenland section is included, the Shield is approximately
circular, bounded on the northeast by the northeast edge of Greenland,
Hudson Bay in the middle. It covers much of Greenland, Labrador,
Quebec north of the St. Lawrence River, much of Ontario
including northern sections of the southern peninsula between the
Great Lakes, the Adirondack Mountains of New York, the northernmost
part of Lower
Michigan and all of Upper Michigan, northern Wisconsin,
northeastern Minnesota, the central/northern portions of
from Hudson Bay, northern Saskatchewan, a small portion of
northeastern Alberta, and the mainland northern Canadian
territories to the east of a line extended north from the
Alberta border (
Northwest Territories and Nunavut). In
total, the exposed area of the Shield covers approximately
8,000,000 km2 (3,088,817 sq mi). The true extent of the
Shield is greater still and stretches from the Western Cordillera in
the west to the Appalachians in the east and as far south as Texas,
but these regions are overlaid with much younger rocks and sediment.
The underlying rock structure also includes Hudson Bay.
Canadian Shield geography in the Flin Flon,
Manitoba region. The lake
in the background is Big Island Lake.
Precambrian pillow lava in the Temagami Greenstone Belt
Canadian Shield is among the oldest on earth, with regions dating
from 2.5 to 4.2 billion years. 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, very tall mountains (about 12,000 metres or 39,000 feet)
with much volcanic activity, but over hundreds of millions 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.[citation
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
Sturgeon Lake Caldera in Kenora District, Ontario, is one of the
world's best preserved mineralized
Neoarchean caldera complexes, which
is 2.7 billion years old. The
Canadian Shield also contains the
Mackenzie dike swarm, which is the largest dike swarm known on
Typical Canadian Shield: spruce, lakes, bogs, and rock.
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
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.
North American craton
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.
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,
is now roughly situated in the
Arctic around the current North Pole.
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 a very dense soil that is not
suitable for forestation; it also contains many marshes and bogs
(muskegs). The rest of the region has coarse soil that does not retain
moisture well and is frozen with permafrost throughout the year.
Forests are not as dense in the north.
Typical landscape in a southern
Ontario region with very few old
growth trees, due to a history of logging and fires. Black River,
Queen Elizabeth II Wildlands Provincial Park.
The Shield is covered in parts by vast boreal forests in the south
that support natural ecosystems as well as a major logging industry.
This boreal forest area includes ecoregions such as the Eastern
Canadian Shield taiga that covers northern
Quebec and most of
Labrador, and the
Midwestern Canadian Shield forests that run
westwards from Northwestern Ontario. Hydrographical drainage is
generally poor, the soil compacting effects of glaciation being one of
the many causes.
Tundra typically prevails in the northern regions.
Many mammals such as caribou, white-tailed deer, moose, wolves,
wolverines, weasels, mink, otters, grizzly bear, 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
Canadian 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 the
Sudbury Basin is an ancient
meteorite impact crater. Ejecta from the meteorite impact was found in
Rove Formation in May 2007. 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.
Flin Flon greenstone belt in central
Manitoba and east-central
Saskatchewan is one of the largest
massive sulfide (VMS) districts in the world, containing 27
copper-zinc-(gold) deposits from which more than 183 million
tons[clarification needed] 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 kilometres (93 mi) depth to
the surface. Currently the Ekati and Diavik mines are actively mining
Volcanology of Canada
Glacial history of Minnesota
^ a b The Atlas of Canada. "Physiographic Regions Map" (JP2). Natural
Resources Canada. Retrieved 2017-08-01.
^ a b Encyclopædia Britannica. "Canadian Shield". Archived from the
original on 2015-06-24. Retrieved 2009-02-10.
^ Stephen Marshak. Essentials of Geology. 3rd ed.
Canadian Shield Archived 2006-08-21 at the Wayback Machine." in
Columbia Encyclopedia. 6th ed., 2005.
^ James-Abra, Erin. "Canadian Shield". Canadian Encyclopedia. Archived
from the original on 11 January 2018. Retrieved 24 January 2018.
^ Corrigan, D. (2008). "Metallogeny and Tectonic Evolution of the
Trans-Hudson Orogen" (PDF). Archived from the original (PDF) on April
9, 2008. Retrieved 2008-03-05.
^ Peterson Field Guide to Geology of Eastern
North America by Roberts,
David & Roger Tory Peterson.
Alberta Heritage -
Alberta Online Encyclopedia Archived 2010-12-08
Archive-It - The
Canadian Shield Region of Alberta
^ Tsuyoshi Iizuka, at al., Geology and Zircon Geochronolgy of the
Acasta Gneiss Complex,
Precambrian Research, 153 (2007) pp. 179 - 208
^ Clark, Bruce W. (1999). "Geologic History". Making Connections:
Canada's geography. Scarborough, Ontario: Prentice Hall Ginn Canada.
p. 95. ISBN 0-13-012635-7.
Caldera Volcanoes Archived 2012-06-16 at
WebCite Retrieved on
^ Mark Pilkington and Walter R. Roest, Removing varying directional
trends in aeromagnetic data, Geophysics, vol. 63 no. 2 (1998), pp.
^ "Barbeau Peak". Bivouac.com.
^ World Wildlife Fund (2001). "Northern
Canadian Shield taiga".
WildWorld Ecoregion Profile. National Geographic Society. Archived
from the original on 2010-03-08.
^ C. Michael Hogan (2008) Polar Bear: Ursus maritimus,
Globaltwitcher.com, ed. Nicklas Stromberg Archived December 24, 2008,
at the Wayback Machine.
^ 3-D Magnetic Imaging using Conjugate Gradients: Temagami anomaly
Archived 2009-07-11 at the Wayback Machine. Retrieved on 2008-03-12
^ Norris, Jessica (2007). "Report on the 2007
Diamond Drilling Program
McClarty Lake Project, Manitoba" (PDF). Aurora Geosciences Ltd.
Archived from the original (PDF) on 2008-05-30. Retrieved
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Schwartzenberger, Tina (2005), The Canadian Shield, Weigl Educational
Pazynych V.G. Formation of placer gold deposits in Canadian Shield
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Coordinates: 52°00′N 71°00′W / 52.000°N 71.000°W /