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Caledonian orogeny
The Caledonian orogeny was a mountain building era recorded in the northern parts of Ireland and Britain, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the continents and terranes of Laurentia, Baltica and Avalonia collided.
The Caledonian orogeny is named for Caledonia, the Latin name for Scotland. The name was first used in 1885 by Austrian geologist Eduard Suess for an episode of mountain building in northern Europe that predated the Devonian period. Geologists like Émile Haug and Hans Stille saw the Caledonian orogeny as one of several episodic phases of mountain building that had occurred during Earth's history.〔McKerrow ''et al.'' (2002)〕 Current understanding has it that the Caledonian orogeny encompasses a number of tectonic phases that can laterally be diachronous. The name "Caledonian" can therefore not be used for an absolute period of geological time, it applies only to a series of tectonically related events.
==Geodynamic history==
The Caledonian orogeny was one of several orogenies that would eventually form the supercontinent Pangaea in the Late Paleozoic era. In the Early Paleozoic the majority of all continental landmasses were united in the paleocontinent of Gondwana, containing the crust of future Africa, South America, southern Eurasia, Australia and Antarctica, which lay centered around the South Pole. Between 650 and 550 million years ago (in the Ediacaran period) the smaller continents of Laurentia (containing the future northeast section of North America), Baltica and Siberia had separated from Gondwana to move northward towards the equator. In the process, the Iapetus Ocean between Gondwana, Baltica and Laurentia closed.
In the Early Ordovician period (about 480 million years ago) the microcontinent (a small fragment of continental lithosphere) Avalonia (at present lithosphere that is scattered over the east of New England, the south of Newfoundland, parts of New Brunswick and Nova Scotia, southern Ireland, most of England and Wales, the low countries and northern Germany) began to separate from the northern margin of Gondwana.〔The exact moment when Avalonia broke off Gondwana is disputed. Here Cocks ''et al.'' (1997) are followed.〕
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