Laurentia is the ancient North American craton, with a basement complex of 1.0 to 3.0 billion-year-old igneous oxides. It has changed shape due to collisions with other cratons, volcanic activity, and sedimentary accretion. It was part of various supercontinents and divided in half by the Western Interior Sea during the Cretaceous period.
Laurentia is another name for the North American craton, the large and very ancient piece of rock on which North America rests. The “basement complex” – the metamorphic and igneous rock beneath the sedimentary layer – of Laurentia is 1.0 to 3.0 billion years old and was created in a tectonically active environment under great pressure and temperature. Its constituent rocks are all igneous oxides, such as granite. Like the other continents, Laurentia is pushed by the expanding oceans, colliding with them and occasionally forming supercontinents such as Pangea.
This landmass gets its name from the Laurentian craton, which takes its name from the St. Lawrence River, which flows over it. The Laurentian craton underlies the entire North American continent, but only reaches the surface in northern Canada, where sedimentary rocks were scraped away during the last ice age. The Laurentian craton is the world’s largest exposed area of Archean rock (older than 2.5 billion years). It features numerous geological spectacles, including the Mackenzie Dam swarm, a 311-mile (500 km) wide and 1,864-mile (3,000 km) long trail of magma cooled by a prodigious eruption 1.2 billion years ago, and the oldest volcanoes in the world.
Over the hundreds of millions of years, Laurentia’s shape has changed slightly, due to collisions with other cratons; volcanic activity, especially large igneous provinces, which can be extruded over the course of a million years; and sedimentary accretion. At the edge of continents is where much of the mountain building takes place, due to the pressure between colliding cratons. The Laurentian craton has mountain ranges on both edges, including the Sierra Nevada to the west and the Appalachian Mountains to the east.
Part of the reason the name “Laurentia” is needed is that the continent has been in various different configurations throughout its history and isn’t necessarily always “north” of anything, making “North America” inappropriate. Laurentia was a component of the supercontinents Kenorland, Nena, Columbia, Rodinia, Protolaurasia, Pannotia, Euramerica, Pangea, Laurasia and the present minor supercontinent, America. For tens of millions of years, during the Cretaceous period, Laurentia was divided in half by the Western Interior Sea. For this reason, various marine fossils can be found in the central United States and Canada.
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