Abstract:

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.

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