Onshore evidence for progressive changes in rifting directions during continental break-up in the NE Atlantic

Current models for the Palaeogene-aged continental break-up in the North Atlantic invoke a NW-SE extension vector throughout the rift-to-drift process, accommodated by margin-parallel normal faults, and margin-oblique (strike-slip) transfer zones. However, Palaeogene and younger faults in the Faroe Islands provide evidence for a progressive anticlockwise rotation in extension vectors immediately prior to and following North Atlantic break-up. Six deformation stages are recognized: (1) east-west to NE-SW extension, accommodated by dip-slip north-south-and NW-SE-trending faults; (2) continued NE-SW extension accommodated by NW-SE-and NNE-SSW-oriented dykes; (3) north-south extension accommodated by ENE-WSW and ESE-WNW conjugate dykes; (4) crustal extrusion involving both east-west shortening and further north-south extension along ENE-WSW (dextral) and ESE-WNW (sinistral) conjugate strike-slip faults; (5) during the final stages of rifting, the regional extension vector became NW-SE and was accommodated predominantly by slip along NE-SW dextral oblique-slip faults; (6) pre-existing structures were locally reactivated as tensional and extensional-shear features, characterized by the entrainment of clastic material along fault planes. The present study reveals a distinct period of margin-parallel extension immediately prior to break-up that is not accounted for by existing models, illustrating the importance of conducting field-based studies to validate otherwise widely accepted margin-scale models worldwide.