The tectonic pattern of Britain and Ireland

The tectonic pattern of Britain and Ireland mainly dates from the Caledonian Orogeny due to closure of the late Neoproterozoic to Silurian Iapetus Ocean that separated the Laurentian continent from Baltica and Avalonia. The Early to Mid-Ordovician collision between Laurentia and an intra-oceanic volcanic arc resulted in the Grampian orogenic event. Eastern Avalonia joined Baltica during the latest Ordovician before early Silurian ‘hard’ collision of Baltica with Laurentia that resulted in the Scandian orogenic event. In contrast, the late Silurian ‘soft’ collision of Eastern Avalonia with Laurentia was not associated with major shortening. Instead sinistral, orogen-parallel motion between Laurentia and Baltica–Avalonia gave strike-slip displacement along major faults in northern Britain into the Early Devonian. During later Early Devonian times, widespread Acadian deformation in Eastern Avalonia probably resulted from the collision of Armorica and Iberia with the southern margin of Avalonia.

In late Carboniferous time, the major Gondwana continent collided with the assembled northern continents, closing the intervening Rheic Ocean and causing the Variscan Orogen. This belt runs west-east across southern Ireland, Wales and England. In Mesozoic time the Pangaea supercontinent began to break up so that extensional basins formed across the British-Irish region. Most basins follow the pre-existing Caledonian and Variscan template. The end of basin extension in mid-Cretaceous time was followed by thermal subsidence, itself terminated in two areas by Paleogene events; plume-related uplift and magmatism in north and west Britain and Ireland and weak shortening across southern England related to the Pyrenean orogeny to the south.