Palaeomagnetic dating of fault rocks: evidence for Permian and Mesozoic movements and brittle deformation along the extensional Dalsfjord Fault, western Norway

Abstract

SUMMARY Palaeomagnetic and structural studies of the Dalsfjord Nappe, western Norway, show that the basal !ow-angle detachment (Dalsfjord Fault) is a long-lived fault zone, and that the most important phase of faulting was of Devonian extension, probably nucleated on an earlier Silurian (Scandian) thrust. Fault rocks produced during subsequent movements indicate that the Dalsfjord Fault underwent periods of brittle low-angle extensional reactivation during the Permian (250-260 Ma) and Upper Jurassic/Lower Cretaceous (c. 150 Ma), corresponding with stages of major extensional movements on the continental shelf. Palaeomagnetic studies may be of great importance for dating faults and major movement stages in long-lived fault systems. The particular importance of the results is that they show that low-angle normal faults can operate in a brittle upper crustal regime.