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Geological Society, London, Special Publications; 1988; v. 38; p. 149-183;
DOI: 10.1144/GSL.SP.1988.038.01.12
© 1988 Geological Society of London

Pre-Arenig Activity in the Caledonian-Appalachian Orogen

Plutonism and volcanism related to the pre-Arenig evolution of the Caledonide-Appalachian orogen

D. W. Rankin, Harald Furnes, A. C. Bishop, B. Cabanis, D. J. Milton, S. J. O’Brien & R. S. Thorpe

U.S. Geological Survey, Mail Stop 926, National Center, Reston, VA 22092, USA
Geologisk Institutt Avd. A, Allegaten 41, 5000 Bergen, Norway
Keeper of Mineralogy, British Museum (Natural History), Cromwell Road, London SW7 5BD, UK
Laboratoire de Géochimie Comparée et Systématique, Tour 16–26, 4 place Jussieu, 75230 Paris Cédex 05, France
U.S. Geological Survey, Mail Stop 928, National Center, Reston, VA 22092, USA
Mineral Development Division, Department of Mines and Energy, PO Box 4750, St John’s, Newfoundland A1C 5T7, Canada
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK

Igneous activity younger than 1 Ga related to crustal extension characterizes the western part of the orogen from N America to Scotland in the Laurentian plate and the eastern part of the orogen in Scandinavia in the Baltic plate. Sub-aerial tholeiites, locally with alkalic rhyolites at embayments, and accompanying mafic dyke-swarms indicate late Proterozoic continental rifting; oceanic tholeiites followed. Iapetus oceanic crust is preserved in ophiolites obducted to the W in Laurentia and to the E in Baltica. Ensimatic island arcs developed locally in late Cambrian and early Ordovician in Scandinavia were broadly coeval with plutonic rocks intruding continental-shelf sediments during the late Finnmarkian deformation in northern Norway. E of the Iapetus suture in N America, southern Britain and northern France many of the igneous rocks of the accreted terranes underwent or were generated during a late Proterozoic orogeny (Avalonian or Cadomian). Locally fossiliferous lower Cambrian strata rest unconformably on calc-alkaline Avalonian or Cadomian granites.

Type I, or cratonal, terranes formed the rifted margins of the Iapetus Ocean. Type II, or accreted, terranes appear not to have been part of the Iapetus rifting cycle and are not now tied stratigraphically to any large cratonal masses. Type II terranes terminate northward against the projection of Tornquist’s line which may have originated in the late Proterozoic as the southern rifted margin of Baltica.





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A. P. M. Vaughan, P. T. Leat, and R. J. Pankhurst
Terrane processes at the margins of Gondwana: introduction
Geological Society, London, Special Publications, 2005; 246: 1 - 21.
[Abstract] [PDF]