A conspectus of Scandinavian Caledonian ophiolites

SUMMARY: Dismembered and fragmented ophiolite assemblages constitute important elements of the metamorphic allochthon ofthe Scandinavian Caledonides. Ophiolites recognized to date range in age from probable Vendian to Middle Ordovician d occur at two principal tectonostratigraphic levels. Field criteria, with support from geochemical data, permit a classification of many of the ophiolite complexes into two fundamental groups. Group I is characterized by a generally well-developed pseudostratigraphy, MORB as well as IAT and WPB petrochemistry, plagiogranites at higher levels, and a conformable cap of oceanic sediments with local ocean r immature arc volcanism. The group is representative of either a major ocean or evolved marginal-basin regime. Evidence points to their obduction, and initial internal deformation, i the Finnmarkian orogenic event in pre-Middle Arenig time. Group II complexes are younger, of late Arenig to Llanvirn and possibly Llandeilo age, and show a poorer-defined pseudostratigraphy. They are laterally and vertically intercalated with either siliciclastic sediments from a contemporary magmatic arc or arcs, and are considered as having been generated in a restricted marginal-basin setting. Their prime tectonic deformation, and translation within nappes, i essentially ofSilurian age. Group I ophiolites were also further dissected and deformed uring this main Caledonian event