Resurgent strike-slip duplex development along the Hitra-Snåsa and Verran Faults, Møre-trøndelag fault zone, Central Norway

Abstract Lineament analysis of the ENE-WSW Verran and Hitra-Snasa Faults of the long-lived More-Trondelag Fault Zone (MTFZ), has revealed the presence of a complex array of anastomosing faults and fractures. This has the geometric configuration of a major, dextral, strike-slip fault zone and compares well with characteristic patterns of braided wrench-faulting, e.g. the San Andreas Fault System of California. The fault array recognized in conjunction with the Verran Fault is clearly post-Caledonian and is considered to define a dextral, strike-slip duplex system. Associated with the parallel Hitra-Snasa Fault are Riedel-like structures which tend to point to an earlier component of sinistral movement. Rock products present along the Hitra-Snasa Fault and its secondary faults comprise mylonites, hydrothermally altered rocks and small-scale recrystallized breccias. Along the main Verran Fault, evidence of late polyphasal deformation is seen in several discrete episodes of brecciation, hydrothermal alteration, and locally pervasive prehnite and stilbite veining. The fault structures occurring along the Hitra-Snasa and Verran faults are thought to have originated as a sinistral fault system of late Devonian age, especially for the Hitra-Snasa lineament. Subsequently, strike-slip movement reversed in sense and shifted locus towards the Verran Fault system during the late Jurassic or early Cretaceous. During this strike-slip reversal, some earlier fractures related to the sinistral system were rejuvenated within the stress field of the evolving dextral duplex system. Strike-slip displacements of a similar age are known from fault complexes on the Norwegian continental shelf and in the northern North Sea. The regional picture indicates that the MTFZ was almost certainly linked to the fault systems of northern Scotland, prior to the opening of the Viking Graben.