Canadian Shield

The Canadian Shield, also called the Laurentian Shield, is a vast expanse of exposed Precambrian igneous and high-grade metamorphic rock forming the ancient geological core, or craton, of North America. It encircles Hudson Bay across eastern, northeastern and east-central Canada and the upper midwestern United States, and, taken together with Greenland, forms a roughly circular pattern; its exposed area covers about 8,000,000 square kilometers, though the same basement rock continues underground much farther, from the Western Cordillera to the Appalachians and as far south as Texas beneath younger cover. Dating puts the shield's oldest rock at up to 4.28 billion years old, with most of the exposed basement between 2.5 and 4.2 billion years old, among the oldest ground anywhere on Earth; repeated glaciation has scraped away the soil across much of the region, leaving bedrock exposed at the surface, including greenstone belts whose mineralized zones formed when erosion stripped away overlying mountains to expose deep crust that had crystallized under conditions favorable to ore formation. This entity documents the Canadian Shield specifically as a geological formation.