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Map of Pangaea with Laurasia and Gondwana.
|Formed||1,071 Mya (Proto-Laurasia) |
|Today part of|
Laurasia (/ - /,), a portmanteau for Laurentia and Eurasia, was the more northern of two supercontinents (the other being Gondwana) that formed part of the Pangaea supercontinent around (Mya). It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pangaea, drifting farther north after the split.
Laurentia, the Palaeozoic core of North America and continental fragments that now make up part of Europe, collided with Baltica and Avalonia in the Caledonian orogeny c. 430–420 Mya to form Laurussia. In the Late carboniferous Laurussia and Gondwana formed Pangaea. Siberia and Kazakhstania finally collided with Baltica in the Late Permian which formed Laurasia. The North China and South China cratons later collided with Siberia.
Laurentia and Baltica first formed a continental mass known as Proto-Laurasia by the convergence and suturing of a series of Archaean continental blocks 1,950-1,800 Mya. Additional Proterozoic crust was accreted 1,800-1,600 Mya of which the only well-preserved sutures are the interior Trans-Hudson orogen and periferal Svecokarelian/Svecofennian orogen.
Laurentia and Baltica formed part of Rodinia, a supercontinent that began to breakup during the Neoproterozoic. As the Proto-Pacific opened 750–600 Mya both continents drifted southward away from the Equator together and rotated clockwise. As they approached the South Pole during the Varanger Glaciation, a mantle plume forced them to separate ca. 650–600 Mya and the Iapetus Ocean opened between them. Laurentia then began to move quickly (20 cm/year (7.9 in/year)) north towards the Equator where it got stuck over a cold spot in the Proto-pacific. Baltica remained near Gondwana in southern latitudes into the Ordovician.
Laurasia — Laurentia, Baltica, and Siberia — remained connected to each other within the short-lived, Precambrian-Cambrian supercontinent Pannotia. At this time a series of continental blocks that now form part of Asia, the Cathaysian terranes — Indochina, North China, and South China — and Cimmerian terranes — Sibumasu, Qiangtang, Lhasa, Afghanistan, Iran, and Turkey — were still attached to the Indian–Australian margin of Gondwana. Other blocks that now form part of southwestern Europe and North America from New England to Florida were still attached to the African-South American margin of Gondwana.
Breakup and reformation
Pannotia broke apart in the late Precambrian into Laurasia, Baltica, Siberia, and Gondwana. The Cadomian–Avalonian, Cathaysian, and Cimmerian terranes then broke away north across the Tethys Ocean.
During the Cambrian, Laurasia was largely located in equatorial latitudes and began to break up, with North China and Siberia drifting into latitudes further north than those occupied by continents during the previous 500 million years. By the Devonian, North China was located near the Arctic Circle and it remained the northernmost land in the world during the Carboniferous Ice Age between 300 and 280 million years ago. No evidence, though, exists for any large-scale Carboniferous glaciation of the northern continents. This cold period saw the rejoining of Laurentia and Baltica with the formation of the Appalachian Mountains and vast coal deposits, found in regions including West Virginia, Britain, and Germany.
Siberia moved southwards and joined with Kazakhstania, a small continental region believed today to have been created during the Silurian by extensive volcanism. When these two continents joined together, Laurasia was nearly reformed, and by the beginning of the Triassic, the East China craton had rejoined the redeveloping Laurasia as it collided with Gondwana to form Pangaea. North China became, as it drifted southwards from near-Arctic latitudes, the last continent to join with Pangaea.
Around 200 million years ago, Laurasia started to break up. Between eastern North America and northwest Africa, a new ocean formed - the Atlantic Ocean, though Greenland (attached to North America) and Europe were still joined together. The separation of Europe and Greenland occurred around 55 million years ago (at the end of the Paleocene). Laurasia finally divided into the continents after which it is named: Laurentia (now North America) and Eurasia (excluding the Indian subcontinent).
|Look up laurasia in Wiktionary, the free dictionary.|
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