Caledonian orogeny

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The Caledonian orogeny is a mountain building event recorded in the mountains and hills of northern Scotland, Ireland, England, Wales, and west Norway. This event occurred during the Silurian and Devonian Periods of the Palaeozoic Era, roughly 444-416 Mya. This orogeny has been named for Caledonia, the Latin name for Scotland.

The Mesozoic Era is marked by the existence of a supercontinent, Pangaea, in which most of the land mass was conjoined into a single large continent surrounded by a single large ocean, Panthalassa. The Caledonian range already existed and was contiguous to the ancestor of the Appalachian Mountains of the eastern United States.

The origin of the Caledonian range occurred earlier, during the assembly of Pangaea by the convergence of more ancient plates. In the preceding Ordovician Period, ca. 488-444 Ma, the largest continent, Gondwana, containing the plates of the future Africa, South America, and Antarctica, was located between the South Pole and the Equator. A second land mass, Laurentia, containing the future northeast section of North America, straddled the equator. To the northeast was the Siberian plate with another continent, Siberia, separated from Gondwana by the Uralian Ocean. To the southeast, the Baltic Plate with the continent Baltica was separated from Gondwana by the Iapetus Ocean. A small archipelago-like continent, Avalonia (containing today's New England, Nova Scotia, and a part of Western Europe including the British Isles) was located west of Baltica, separated from it by the Tornquist Ocean. The Rheic Ocean lay between Avalonia and Baltica to the north and Gondwana to the south.

In the Ordovician Period, the Rheic Ocean began to open, pushing Baltica and Avalonia in the direction of Laurentia by sea-floor spreading. Baltica and northern Avalonia collided first, causing the Caledonian Orogeny of the Silurian. At the end of the Silurian and in the subsequent Devonian, the rest of Avalonia collided, causing the Acadian Orogeny of North America, which raised the early Appalachian Mountains.

See also

• Scandinavian Mountains

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