Avalon terrane

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. It is the source of many of the older rocks of Western Europe, Atlantic Canada, and parts of the coastal United States. Avalonia is named for the Avalon Peninsula in Newfoundland.

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, then Laurentia, and finally with Gondwana, ending up in the interior of Pangea. When Pangea broke up, Avalonia's remains were divided by the rift which became the Atlantic Ocean.

The early development of 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, the supercontinent Pannotia broke 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 Baltica slowly rotated counterclockwise towards it. This happened at the end of the Ordovician and during the early Silurian.

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