Ancient scars and rotating ribbons: how Appalachian-Caledonian orogenic inheritance seeded the rotations of the Flemish Cap and the Porcupine Bank during the Mesozoic rifting of the North Atlantic Ocean

The rifted continental margins of the modern Atlantic Ocean, spanning from pole to pole, encompass the full gamut of margin types and structural styles, with the Newfoundland-Iberia margins arguably having received the greatest amount of scientific scrutiny and attention. Still, the most interesting segment of the Atlantic appears to correspond to the Newfoundland-Galician conjugates and the Newfoundland-Irish Atlantic conjugates, where classic passive margin templates are suddenly replaced by failed rifts and numerous continental ribbons, still tethered to their continents (e.g., Flemish Cap and Porcupine Bank). This region of increased complexity corresponds exactly with the intersection of the Mesozoic rift with pre-existing, and obliquely-oriented, scars from the Paleozoic Appalachian-Caledonian Orogen, providing a world-class laboratory for investigating the influence of inheritance on rifting.

A recently published numerical modelling study, simulating the interaction of propagating rifts, revealed that such rifts, when laterally offset by approximately 400 km, can successfully generate and rotate continental ribbons away from their respective rifted continental margins. In particular, that study provided a compelling mechanism to explain the rotation of the Flemish Cap. In this work, we argue for the broader extrapolation of those modelling results to explain the rotations of both the Flemish Cap, offshore Newfoundland, and the Porcupine Bank, offshore Ireland, with the first rift corresponding to the northward propagating Atlantic rift and the second apparent rift corresponding to reactivated Appalachian-Caledonian scars. Consistent with the numerical modelling results, this conceptual rifting model results in failed rifts both within the Orphan Basin, offshore Newfoundland, and within the Porcupine Basin, offshore Ireland, with those failed rift features supported by numerous complementary geophysical studies. Future numerical modelling efforts will be dedicated to testing this relatively simple model of rift-inheritance interactions for the southern North Atlantic to confirm that they are sufficient to explain the observed complexity of margin structures between offshore Newfoundland and its conjugates.