Canadian Shield - Geographical Extent

Geographical Extent

The 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 as the Adirondack Mountains (connected by the Frontenac Axis) and the Superior Upland. The Canadian Shield is U-shaped, but almost semi-circular, which yields an appearance of a warrior's shield, 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 is more than 2 billion years old. The Canadian Shield once had jagged peaks, but millions of years of erosion have changed these mountains to rolling hills.

The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic eon 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 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 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.r

When the Greenland section is included, the Shield is approximately circular, bounded on the northeast by the northeast edge of Greenland, with Hudson Bay in the middle. It covers much of Greenland, Labrador, most of 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 northern New York, the northernmost part of Lower Michigan and all of Upper Michigan, northern Wisconsin, northeastern Minnesota, the central/northern portions of Manitoba away 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 Saskatchewan/Alberta border (Northwest Territories and Nunavut). In total, it covers approximately 8,000,000 km2 (3,088,817 sq mi). 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.