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AVALONIA was a microcontinent in the Paleozoic era . Crustal fragments of this former microcontinent underlie south-west Great Britain , and the eastern coast of North America
North America
. It is the source of many of the older rocks of Western Europe
Western Europe
, Atlantic Canada, and parts of the coastal United States
United States
. Avalonia
Avalonia
is named for the Avalon Peninsula in Newfoundland .

Avalonia
Avalonia
developed as a volcanic arc on the northern margin of Gondwana . It eventually rifted off, becoming a drifting microcontinent. The Rheic Ocean formed behind it, and the Iapetus Ocean shrank in front. It collided with the continents Baltica
Baltica
, then Laurentia , and finally with Gondwana, ending up in the interior of Pangea
Pangea
. When Pangea
Pangea
broke up, Avalonia's remains were divided by the rift which became the Atlantic Ocean
Atlantic Ocean
.

CONTENTS

* 1 Development * 2 Consequences * 3 See also * 4 References * 5 External links

DEVELOPMENT

Schematic diagram of the paleogeographic evolution of Avalonia, Baltica
Baltica
and Laurentia. (Names in German.) Location of the Caledonian/Acadian mountain chains in the Early Devonian
Devonian
Epoch. Present day coastlines are shown for reference. Red lines are sutures, capitalized names are the different continents/super-terranes that joined during the Caledonian orogeny. The Old Red Sandstone Continent
Continent
in the Devonian
Devonian

The early development of Avalonia
Avalonia
is believed to have been in volcanic arcs near a subduction zone on the margin of Gondwana . 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 .

In the early Cambrian
Cambrian
, the supercontinent Pannotia
Pannotia
broke up and Avalonia
Avalonia
drifted off northwards from Gondwana. This independent movement of Avalonia
Avalonia
started from a latitude of about 60° South. The eastern end of Avalonia
Avalonia
collided with Baltica
Baltica
, a continental plate occupying the latitudes from about 30°S to 55°S, as Baltica
Baltica
slowly rotated counterclockwise towards it. This happened at the end of the Ordovician
Ordovician
and during the early Silurian
Silurian
.

In the late Silurian
Silurian
and lower Devonian
Devonian
, the combined Baltica
Baltica
and Avalonia
Avalonia
collided progressively, with Laurentia , beginning with the long extremity of Avalonia
Avalonia
which is now attached to the USA and Canada. 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
North America
as an early phase in the Acadian orogeny .

In the Permian
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
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
Carboniferous
, forming Pangaea
Pangaea
with Avalonia
Avalonia
near its centre but partially flooded by shallow sea.

In the Jurassic
Jurassic
, Pangaea
Pangaea
split into Laurasia
Laurasia
and Gondwana, with Avalonia
Avalonia
as part of Laurasia. In the Cretaceous
Cretaceous
, Laurasia
Laurasia
broke up into North America
North America
and Eurasia
Eurasia
with Avalonia
Avalonia
split between them.

Iberia was later rotated away again as the African part of Gondwana strike-slipped past it. This last movement caused the Alpine orogeny including the raising of the Pyrenees
Pyrenees
during the Miocene
Miocene
and Pliocene . As a result of this, part of Avalonia
Avalonia
is now to be found on each side of the Straits of Gibraltar .

CONSEQUENCES

This map shows the positions of the rocks of Avalonia
Avalonia
remaining in Europe. The notes on it indicate the part which collided with Baltica
Baltica
in the upper Ordovician
Ordovician
and that which collided with Laurentia in the Silurian. The parts of Avalonia
Avalonia
now in Iberia and Morocco were carried there by rotation of Iberia during the subsequent collision with Gondwana followed by separation. These rocks are by no means all at the modern surface.

The Avalonian part of Great Britain
Great Britain
almost exactly coincides with England and Wales. Elsewhere in Europe
Europe
, parts of Avalonia
Avalonia
are found in the Ardennes
Ardennes
of Belgium
Belgium
and north-eastern France
France
, north Germany
Germany
, north-western Poland
Poland
, south-eastern Ireland
Ireland
, and the south-western edge of the Iberian Peninsula
Iberian Peninsula
.

Part of the British-Belgian section formed an island in the Carboniferous, affecting the disposition of coalfields; this is known by names such as the ' London-Brabant Island '. Its bulk had an effect on the geological structure between the Ardennes
Ardennes
and the English Midlands by influencing the subsequent crustal folding resulting from the Variscan collision.

In Canada
Canada
, Avalonia
Avalonia
comprises the Avalon Peninsula of southeast Newfoundland , southern New Brunswick
New Brunswick
, part of Nova Scotia
Nova Scotia
, and Prince Edward Island
Prince Edward Island
. In the United States
United States
, Avalonia
Avalonia
consists of northern coastal Maine
Maine
, all of Rhode Island
Rhode Island
, and other sections of coastal New England
New England
.

SEE ALSO

* Mistaken Point, Newfoundland and Labrador

REFERENCES

* ^ Murphy, J. B.; Pisarevsky, S. A.; Nance, R. D.; Keppie, J. D. (2001). Jessell, M. J., ed. "Animated history of Avalonia
Avalonia
in Neoproterozoic - Early Proterozoic" (PDF). General Contributions. Journal of the Virtual Explorer. 3: 45–58. Retrieved November 2015. Check date values in: access-date= (help ) * ^ Strachan, R. A. (2000). "Late Neoproterozoic to Cambrian accretionary history of Eastern Avalonia
Avalonia
and Armorica on the active margin of Gondwana". In Woodcock, N. H.; Strachan, R. A. Geological History of Britain and Ireland. Blackwell. pp. 127–139. Retrieved November 2015. Check date values in: access-date= (help )

EXTERNAL

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