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Laurentia or the North American craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and the Hebridean terrane in northwest Scotland. During other times in its past, Laurentia has been part of larger continents and and consists of many smaller assembled on a network of early Proterozoic Orogenic belt. Small and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.
The oldest bedrock, assigned to the Archean Slave craton, Rae craton, Hearne craton, Wyoming craton, Superior craton, and Nain Province Provinces, is located in the northern two thirds of Laurentia. During the Early Proterozoic they were covered by sediments, most of which has now been eroded away.
Greenland is part of Laurentia. The island is separated from North America by the Nares Strait, but this is a Pleistocene erosional feature. The strait is floored with continental crust and shows no indications of a thermal event or seaway tectonism. Greenland is composed mostly of crust of Archean to Proterozoic age, with lower Paleocene shelf formations on its northern margin and Devonian to Paleogene formations on its western and eastern margins. The eastern and northern margins were heavily deformed during the Caledonian orogeny.
The Isua Greenstone Belt of western Greenland preserves oceanic crust containing sheeted dike complexes. These provide evidence to geologists that mid-ocean ridges existed 3.8 Ga. The Abitibi gold belt in the Superior Province is the largest greenstone belt in the Canadian Shield.
The resulting nucleus of Laurentia was mostly reworked Archean crust but with some juvenile crust in the form of volcanic arc belts. Juvenile crust is crust formed from magma freshly extracted from the Earth's mantle rather than recycled from older crustal rock. The intense mountain building of the Trans-Hudson orogeny formed thick, stable roots beneath the craton, possibly by a process of "kneading" that allowed low density material to move up and high density material to move down.
Over the next 900 million years, Laurentia grew by the accretion of Island arc and other juvenile crust and occasional fragments of older crust (such as the Mojave block). This accretion occurred along the southeastern margin of Laurentia, where there was a long-lived convergent plate boundary. Major accretion episodes included the Yavapai orogeny at 1.71 to 1.68 Gya, which welded the 1.8 to 1.7 Gya Yavapai province to Laurentia; the Mazatzal orogeny at 1.65 to 1.60 Gya, accreting the 1.71 to 1.65 Gya Mazatzal province; the Picuris orogeny at 1.49 to 1.45 Gya, which may have welded the 1.50 to 1.30 Gya Granite-Rhyolite province to Laurentia; and the Grenville orogeny at 1.30 to 0.95 Gya, which accreted the 1.30 to 1.00 Gya Llano-Grenville province to Laurentia.
The Picuris orogeny, in particular, was characterized by the intrusion of great volumes of granitoid magma into the juvenile crust, which helped mature the crust and stitch it together. Slab rollback at 1.70 and 1.65 Gya deposited characteristic quartzite-rhyolite beds on the southern margin of the craton. This long episode of accretion doubled the size of Laurentia but produced craton underlain by relatively weak, hydrous, and fertile (ripe for extraction of magma) mantle lithosphere. The subduction under the southeast margin of the continent likely caused enrichment of the Lithosphere mantle beneath the orogenic belts of the Grenville Province. Around 1.1 Gya, the center of the craton nearly rifted apart along the Midcontinent Rift System. This produced the Keweenawan Supergroup, whose are rich in copper ore.
Recent evidence suggests that South America and Africa never quite joined to Rodinia, though they were located very close to it. Newer reconstructions place Laurentia closer to its present-day orientation, with East Antarctica and Australia to the west, South China to the northwest, Baltica to the east, and Amazonia and Rio de la Plata to the south.
The breakup of Rodinia began by 780 Ma, when numerous mafic were emplaced in western Laurentia. Early stages of rifting produced the Belt Supergroup, which is over thick. By 750 Ma the breakup was mostly complete, and Gondwana (composed of most of today's southern continents) had rotated away from Laurentia, which was left isolated near the equator. The breakup of Rodinia may have triggered an episode of severe ice ages (the Snowball Earth hypothesis.)
The breakup of Pannotia produced six major continents: Laurentia, Baltica, Kazakhstania, Siberia, China, and Gondwana. Laurentia remained an independent continent until the middle Silurian. During the early to middle Ordovician, several volcanic arcs collided with Laurentia along what is now the Atlantic coast of North America. This caused an episode of mountain-building called the Taconic orogeny. As the mountains raised by the Taconic orogeny were subsequently eroded, they produced the immense Queenston Delta, recorded in the rocks of the Queenston Formation. There was also violent volcanic activity, including the eruption that produced the Millburg/Big Bentonite ash bed. About of ash erupted in this event. However, this does not seem to have triggered any mass extinction.
Throughout the early Paleozoic, Laurentia was characterized by a tectonically stable interior flooded by the seas, with marginal Orogenic belt. An important feature was the Transcontinental Arch, which ran southwest from the lowlands of the Canadian Shield. The shield and the arch were the only portions of the continent that were above water through much of the early Paleozoic. There were two major marine transgressions (episodes of continental flooding) during the early Paleozoic, the Sauk and the Tippecanoe. During this time, the Western Cordillera was a passive margin. Sedimentary rocks that were deposited on top of the basement complex were formed in a setting of quiet marine and river waters. The craton was covered by shallow, warm, tropical epicontinental or epicratonic sea (meaning literally "on the craton") that had maximum depths of only about 60 m (200 ft) at the shelf edge.
The position of the equator during the Late Ordovician epoch ( Ma) on Laurentia has been determined via extensive shell bed records. Flooding of the continent that occurred during the Ordovician provided the shallow warm waters for the success of sea life and therefore a spike in the carbonate shells of shellfish. Today the beds are composed of fossilized shells or massive-bedded Thalassinoides facies and loose shells or nonamalgamated brachiopod shell beds. These beds imply the presence of an equatorial climate belt that was hurricane free which lay inside 10° of the equator. This ecological conclusion matches the previous paleomagnetic findings which confirms this equatorial location.
During this time, several small continental fragments merged with other margins of the craton. These included the North Slope of Alaska, which merged during the Early Devonian. Several small crust fragments accreted from the late Devonian through the Mesozoic to form the Western Cordillera.
The Western Cordillera became a convergent plate margin during the Ordovician, and the Transcontinental Arch became submerged, only to reappear in the Devonian. The Devonian also saw the deposition of the Chattanooga Shale and the Antler Orogeny in the Western Cordillera.
During the Pennsylvanian, the Ancestral Rocky Mountains were raised in the southwestern part of Laurentia. This has been attributed either to either the collision with Gondwana or subduction under the continental margin from the southwest. (2025). 9781607810049, University of Utah Press. ISBN 9781607810049 Two additional marine transgressions took place during the late Paleozoic: the Kaskaskia and Absaroka.
The great continental mass of Pangaea strongly affected climate patterns. The Permian was relatively arid, and were deposited in the Permian Basin. Sedimentary beds deposited in the southwest in the early Triassic were fluvial in character, but gave way to eolian beds in the late Triassic. Pangaea reached its height about 250 Ma, at the start of the Triassic.
The Gulf of Mexico opened during the Late Triassic and Jurassic. This was accompanied by deposition of evaporite beds that later gave rise to that are important petroleum reservoirs today. Europe rifted away from North America between 140 and 120 Ma, and Laurentia once again became the core of an independent continent with the opening of the North Atlantic in the Paleogene.
Four orogeny occurred in the Mesozoic in the Western Cordillera: the Sonoma orogeny, Nevadan orogeny, Sevier orogeny, and Laramide orogeny. The Nevadan orogeny emplaced the extensive batholiths of the Sierra Nevada. The regression of the Sundance Sea in the late Jurassic was accompanied by deposition of the Morrison Formation, notable for its vertebrate fossils.
During Cretaceous times, the Western Interior Seaway ran from the Gulf of Mexico to the Arctic Ocean, dividing North America into eastern and western land masses. From time to time, land masses or mountain chains rose up on the distant edges of the craton and then eroded down, shedding their sand across the landscape. Chalk beds of the Niobrara Formation were deposited at this time, and accretion of crustal fragments continued along the Western Cordillera.
The southwestern portion of Laurentia consists of Precambrian basement rocks deformed by continental collisions. This area has been subjected to considerable rifting as the Basin and Range Province has been stretched up to 100% of its original width. The area experienced numerous large volcanic eruptions. Baja California rifted away from North America during the Miocene. This block of crust consists of Proterozoic to early Paleozoic shelf and Mesozoic arc volcano formations. The Holocene being an interglacial, a warm spell between episodes of extensive glaciation.
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