Timing of Caledonian Evorogenic Activity in the Scandinavian Caledonides

Abstract

RECENT discussion of the precise timing, extent and intensity of late Cambrian and early Ordovician movements and metamorphism in the Caledonian orogen, and in Scandinavia in particular, has concentrated on graptolite faunal studies^1–5 and radiometric age determinations^6,7. In Norway, interest has centred on the West Finnmark and Trondheim regions following the revelation of an early Ordovician evorogenic event in Finnmark; in compiling evidence çorrelatable with this period of folding, intrusion and metamorphism, Sturt et al.⁶ tended to overemphasize the significance of the Trondhjem (Trondheim) disturbance⁸ so that later workers^3,5,9 have mistakenly promoted this parorogenic episode to the status of an important deformation and metamorphism. Concern has been voiced in Scandinavian circles over this repeated misuse of Holtedahl's term⁸, which was originally used to define a local unconformity where a conglomerate overlies a greenstone sequence. Similar crustal movements recognized higher up in the stratigraphy, the Ekne and Horg disturbances of Vogt¹⁰, have analogues in minor breaks occurring in the Appalachian¹¹ and British Caledonian¹² Lower Palaeozoic successions. As the evolution of the Caledonian-Appalachian orogen is now being reassessed in the light of the plate tectonics philosophy^13,14, it is timely to review aspects of the Norwegian evidence before further models are proposed.