EVIDENCE FOR OPHIOLITE OBDUCTION, TERRANE ACCRETION AND POLYOROGENIC EVOLUTION OF THE NORTH SCANDINAVIAN CALEDONIDES

Recent work on the thrust sheets of the Ofoten-Troms region, north Nor wegian Caledonides, has resulted in revision of the tectonostratigraph ic correlations providing new constraints on models for terrane accret ion and poly-orogenic Cambro-Ordovician and Siluro-Devonian developmen t. Previous studies on Late Ordovician-Early Silurian fossils in metas ediments unconformably overlying the Lyngen Ophiolite complex within o ne of the Troms nappes documented a period of ophiolite obduction prio r to the major Siluro-Devonian Scandian orogenic event. Correlation of these units and underlying and overlying thrusts sheets southward int o the Ofoten area, 150 km to the south, is demonstrated. This implies that an extensive, completely transported, Upper Ordovician-Lower Silu rian basin, developed on top of the obducted ophiolite, composes the b edrock of much of northern Norway. Metamorphism and deformation within these basinal rocks resulted from the Scandian phase of the Caledonia n orogeny. The relatively weak metamorphic and deformational imprint o n the ophiolitic basement provides a rare opportunity to evaluate the pre-Scandian tectonic evolution of northern Scandinavia. Poly-orogenic evolution, a controversial subject in northern Norway, is documented. The character and relative extent of Cambro-Ordovician and Siluro-Dev onian orogenic zones in northern Norway are elucidated. The Balsfjord/ Ofoten unconformity formed approximately concomitant with other post-o phiolite obduction unconformities in central and southern Norway, impl ying an orogen-wide Late Cambrian-Early Ordovician event.