Reinterpretation of Finnmarkian deformation on western Sørøy, northern Norway

New field observations of the relationships between dikes of the Seiland Igneous Province and psammites of the Klubben Group on western Sørøy have led to the interpretation that the psammites were not deformed or folded by orogenesis either before or during intrusion of the dikes. Folds with axial planes parallel to the dikes developed after dike intrusion, and the dikes appear to cut undeformed sedimentary bedding and intrusion-related migmatitic textures and fold structures, not orogenic foliations and folds. These results contrast with previous studies which concluded that the Late Cambrian to Early Ordovician Seiland intrusions on Sørøy were syn-orogenic, interpretations originally used to define the Finnmarkian phase of the Caledonian orogeny. Relationships between Seiland intrusions and country rocks elsewhere in Finnmark, and other evidence for Finnmarkian regional metamorphism and thrust tectonics in northern Norway, should thus be re-examined. The syenites, carbonatites, layered gabbros and ultramafic rocks of the Seiland Igneous Province may be related to continental rifting and development of the Iapetus ocean; not mantle diapirism within a subduction zone, as previously interpreted.