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Pre-Arenig Activity in the Caledonian-Appalachian Orogen |
Department of Geology, Royal Holloway & Bedford New College, University of London, Egham, Surrey TW20 0EX, UK
Geologisk Institutt Avd. A, Universitetet i Bergen, 5000 Bergen, Norway
United States Geological Survey, Reston, VA 22092, USA
Department of Geology, University of Massachusetts, Amherst, MA 01003, USA
Department of Mines and Energy, PO Box 1087, Halifax, Nova Scotia, Canada
Available isotopic data suggest that the Precambrian basement elements of the northern parts of the Caledonide orogen in N America, Britain, Ireland, Greenland and Scandinavia comprise largely Grenvillian and Svecofennian continental crust. Archaean precursors have been identified in Greenland, Norway and Britain, but not positively in the Appalachians. Early Caledonian (Grampian-Finnmarkian) orogenic activity gave rise, in the Scandinavian and British-Irish sectors, to an early Palaeozoic basement which, in Norway, is overlain by Ordovician to Silurian supracrustal sequences. In contrast, a late Precambrian-early Cambrian (Cadomian-Avalonian and older) basement is present in southern parts of the orogen.
The distribution of these basement elements constrains any plate-tectonic reconstructions of the N Atlantic Caledonide orogen and suggests that the orogen was tripartite during its early development. Further, it suggests that transcurrent movements as well as obduction may have been important tectonic processes during Grampian-Finnmarkian tectonism.
