Avalonia

Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent are terranes in parts of the eastern coast of North America: Atlantic Canada, and parts of the East Coast of the United States. In addition, terranes derived from Avalonia also make up portions of Northwestern Europe, being found in England, Wales and parts of Ireland.

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. The Armorican Terrane assemblage collided with the merged Baltica/Avalonia during the formation of Pangea. When Pangea broke up, Avalonia's remains were divided by the rift which became the Atlantic Ocean.

Avalonia is named for the Avalon Peninsula in Newfoundland.

When the term "Avalon" was first coined by Canadian geologist Harold Williams in 1964, he included only Precambrian rocks in eastern Newfoundland. More than a decade later he extended the term to include all exotic rocks from Newfoundland down to Rhode Island. Since the introduction of the term terrane in the 1980s, Avalonia has been referred to as "platform", "composite terrane", "superterrane", "East" and "West Avalonia", and "Avalon sensu lato". "Avalonia" can thus refer exclusively to rocks in Newfoundland (Avalonia sensu stricto), an assembly of terranes, or a single tectonic unit.