Avalonia was an ancient
microcontinentor terranewhose history formed much of the older rocks of Western Europe, Atlantic Canada, and parts of the coastal United States. The name is derived from the Avalon Peninsulain Newfoundland.
The early development of Avalonia is believed to have been in
volcanic arcs near a subduction zoneon the margin of Gondwana. [ [http://virtualexplorer.com.au/journal/2001/03/murphy/paper2.html Virtual Explorer] ] Some material may have accreted from volcanic island arcs which formed further out in the ocean and later collided with Gondwana as a result of plate tectonic movements. The igneous activity had started by 730 million years ago and continued until around 570 million years ago, in the late Neoproterozoic. [Woodcock, N. & Strachan, R., eds, (2000) "Geological History of Britain and Ireland", Blackwell, pp 127-139.]
In the early
Cambrian, the supercontinent Pannotiabroke up and Avalonia drifted off northwards from Gondwana. This independent movement of Avalonia started from a latitude of about 60° South. The eastern end of Avalonia collided with Baltica, a continental plate occupying the latitudes from about 30°S to 55°S, as the latter slowly rotated anticlockwise towards it. This happened at the end of the Ordovicianand during the early Silurian.
In the late
Silurianand lower Devonian, the combined Baltica and Avalonia collided progressively, with Laurentia, beginning with the long extremity of Avalonia which is now attached to America. The result of this was the formation of Euramerica. At the completion of this stage, the site of Britain was at 30°S and Nova Scotia at about 45°S. This collision is represented by the Caledonian folding or in North America as an early phase in the Acadian orogeny.
Permian, the new continent and another terrane, Armorica which included Iberia, drifted in from Gondwana, trapping Avalonia between it and the continent so adding Iberia/Armorica to Euramerica. This was followed up by the arrival of Gondwana. The effects of these collisions are seen in Europe as the Variscan folding. In North America it shows as later phases of the Acadian orogeny. This was happening at around the Equator during the later Carboniferous, forming Pangaeain such a way that Avalonia was near its centre but partially flooded by shallow sea.
Jurassic, Pangaea split into Laurasiaand Gondwana, with Avalonia as part of Laurasia. In the Cretaceous, Laurasia broke up into North Americaand Eurasiawith Avalonia split between them.
Iberia was later rotated away again as the African part of Gondwana brushed past. This last movement caused the
Alpine orogenyincluding the raising of the Pyreneesduring the Mioceneand Pliocene. As a result of this, part of Avalonia is now to be found on each side of the Straits of Gibraltar.
In the modern world, we see Avalonia as forming the basic structure of the
Ardennesof Belgiumand north-eastern France, north Germany, north-western Poland, England, Wales, south-eastern Ireland, the south-western edge of the Iberian Peninsula, the Avalon Peninsula, much of Nova Scotia, southern New Brunswickand parts of New England. See map 2, Acadian Orogenyand The Acadian orogeny.
The Avalonian part of Britain almost exactly coincides with England and Wales. Part of this which had formed an island in the Carboniferous, so affecting the disposition of coalfields, is known by names such as the '
London-Brabant Island'. Its bulk had an effect on the geological structure between the Ardennes and the English Midlandsby influencing the subsequent crustal folding resulting from the Variscan collision.
Canada, Avalonia comprises the Avalon Peninsulaof southeast Newfoundland, portions of New Brunswick, Nova Scotia, Prince Edward Island. In the United States, Avalonia comprises northern coastal Maine, other sections of coastal New England, and sections of coastal North Carolina.
* [http://upload.wikimedia.org/wikipedia/de/e/e4/Avalonia_entwicklung_odovizium_silur.png] These maps show the relative positions of the terranes and continental plates at various stages in the Ordovician, Silurian and Devonian respectively. The names shown are in their German forms.
Iceland- a microcontinent
Mistaken Point (Newfoundland and Labrador)
* [http://palaeos.com/Earth/Geography/Avalonia.htm Article about Avalonia at Palaeos.Com] (licensed under Attribution-NonCommercial 1.0 complete with pictures)
* [http://www.dinodata.net/Golonka/phan.pdf The context of Avalonia's movements] (not available without registration)
* [http://www.globalchange.umich.edu/Ben/Publications/gsab01.pdf Relative positions of Avalonia and Gondwana]
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