A tectonic model for the evolution of the Finnmarkian Caledonides of North Norway

Abstract

A revision of previous plate models for the evolution of the Finnmarkian orogen in North Norway, based on new structural, palaeogeographical, palaeontological, and geochemical evidence is proposed. In this model, two zones of crustal extension occurred within the Laurentia–Baltica craton, as preserved in North Norway. The eastern zone (Gaissa Basin) was an aulacogen that was filled by shallow-marine to fluviatile sediments, including dolomitic and sabkha facies, overlain by glacial and further shallow-marine deposits of Vendian age. The western zone developed into the Iapetus Ocean in which a transgressive sequence of shallow-marine sandstones and mudstones was followed by sporadic carbonate facies and, finally, distal turbidites. Development of the Gaissa Basin during the late Riphean was followed by the rifting of the Iapetus Ocean somewhat later, in the early Sinian. The two basins were separated by a topographic high, the Finnmark Ridge, which became submerged during the earliest Vendian. These ages have been inferred from the proposed stratigraphic correlations and by the qualitative application of modem concepts of continental-margin development. Metabasic dykes within the 3.3 km thick Iapetus Ocean sediments have been related to an unspecified period of tension, post-Iapetus rifting, and not to Iapetus rifting as previously inferred. Comparison of this model with those from central Scandinavia shows marked discrepancies; it is postulated (but not demonstrated) that the age of rifting in central Scandinavia may have been considerably older than previously interpreted from the emplacement ages of the Ottfjället metadolerite dykes.