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Laurentia



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Laurentia, also called the North American craton.

Laurentia (or North American Craton) is a large continental craton. It forms the ancient geological core of the North American continent. Originally, it included core of Greenland and the northwestern part of Scotland, known as the Hebridean Terrane.

During other times in its past, Laurentia has been part of larger continents and supercontinents. It is an assembly of smaller tectonic plates which merged early in the Palaeoproterozoic era. As the plates moved together, a huge range of mountains formed. Small plates and oceanic islands collided with and fused with the ever-growing Laurentia. Together they made the huge, stable craton we see today as the north and west of North America and Greenland.[1]

The remaining, western, part of North America was added much later, after Pangaea split up, and the Americas moved west from Eurasia and Gondwana.

The craton is named after the Laurentian Mountains.

Rocks as seen today

The cratonic rocks are metamorphic and igneous, while the overlying sedimentary rocks are composed mostly of limestones, sandstones, and shales.[2] These sedimentary rocks were deposited from 650 to 290 million years ago.[3] In eastern and central Canada, much of the stable craton is exposed at the surface.

The southwestern portion of Laurentia consists of Precambrian basement rocks deformed by continental collisions (violet area of the image above). This area has been subjected to considerable rifting as the Basin and Range Province and has been stretched up to 100% of its original width.[4] The area has a history of major volcanic eruptions.

References

  1. Dalziel I.W.D. 1992. "On the organization of American plates in the Neoproterozoic and the breakout of Laurentia". GSA Today 2 (11): 237–241.
  2. Sloss, L.L. (1988). "Conclusions, Chapter 17: The Geology of North America". Sedimentary cover - North American Craton. D-2. pp. 493–496.
  3. Burgess, P.M. Gurnis, M., and Moresi, L. (1997). "Formation of sequences in the cratonic interior of North America by interaction between mantle, eustatic, and stratigraphic processes". Geological Society of America Bulletin 109 (12): 1515–1535. doi:10.1130/0016-7606(1997)109<1515:FOSITC>2.3.CO;2 .
  4. "Geologic provinces of the United States: Basin and Range Province". USGS.gov website. http://geomaps.wr.usgs.gov/parks/province/basinrange.html. Retrieved 9 November 2009.