Geochemistry of Upper Riphean-Vendian basalts associated with the ‘sparagmites’ of southern Norway

Abstract

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.

A conspectus of Scandinavian Caledonian ophiolites

“…Turning to the nearby island of Bomlo, the Lykling Ophiolite was strongly folded, and in places inverted, before being unconformably overlain by bimodal continental volcanics (NordAs et al 1983) now reliably dated as Middle Ordovician in age (Furnes et al 1983a). An ensimatic island arc was developed on the edifice of oceanic crust with extensive eruption of low-K tholeiites and keratophyres (Nord~s et al 1983) which have recently been dated at 535 + 46 Ma (Furnes et al 1983a).…”

“…An ensimatic island arc was developed on the edifice of oceanic crust with extensive eruption of low-K tholeiites and keratophyres (Nord~s et al 1983) which have recently been dated at 535 + 46 Ma (Furnes et al 1983a). This latter dating shows that the ophiolite itself must represent older oceanic crust.…”

“…Firstly, evidence for transform faulting is restricted to the southernmost localities (Karmoy, Lykling) where features of the sedimentary cap-rocks, and rotational patterns of sheeted dykes are strongly suggestive of transform activity (Amaliksen 1980;Solli 1981). Thick developments of ultramafic cumulates, often with chromite concentrations, and the only instances yet recorded of upper-mantle tectonites (Table 1) are confined to Leka and other occurrences in the Helgeland Nappe Complex (Furnes et al 1980b;Prestvik 1980). As shown by Furnes et al (1982) there are also regional differences in the geochemical patterns which are summarized below.…”

“…1) (Roberts et al 1983a), their actual location within the nappe pile has been complicated in some areas by multicomponental thrusting and slicing with resultant repetition of stratigraphies. In this contribution we outline the basic divisions of the ophiolite types and their distribution, and note the character and importance of major unconformities and tectono-metamorphic breaks throughout the mountain belt.…”

Chapter 59 Neoproterozoic glaciation of South Norway: from continental interior to rift and pericratonic basins in western Baltica

“…rests with depositional contact within the Hedmark Group on (1) coarse-grained fan-delta sandstones of the Ring Fm., (2) carbonate platform and shale beds of the Biri Fm., (3) fluvial sandstones of the Rendalen Fm., (4) shallow-marine sandstones of the Atna Fm. and (5) (Nystuen 1982(Nystuen , 1987Furnes et al 1983). Basalt clasts in marine canyon infill conglomerates of the Biskopåsen Formation located at the top of the Brøttum Fm.…”