Summary. Upper Riphean/Vendian basalt lavas within the Hedmark Group of the Osen-Røa Nappe Complex, the lowest tectonostratigraphic unit within the Scandinavian Caledonides, are typical continental tholeiites. Differences in their REE patterns may reflect source heterogeneities, while the general lack of correlation between incompatible trace element ratios may be due to contamination of the basalts by continental crust. Their association with fluvial deposits in NNW-trending graben, and some geochemical disparities with time-equivalent basalt dykes of MORB-like character in tectonically higher units, may indicate their formation in an aulacogen related to the central rift zone of the lapetus Ocean.