The deep structure of the Porcupine Basin, offshore Ireland, from gravity and magnetic studies

Marine gravity and magnetic surveys around Ireland, together with satellite gravity data from the deeper ocean, are used to investigate the large-scale crustal structure of the Porcupine Basin, offshore west of Ireland. The structure of the syn-rift to post-rift sedimentary successions, derived from vertical incidence seismic reflection data, is used to isolate the gravity and magnetic responses of the crust and mantle. The crustal structure derived from wide-angle seismic data in the region is used to control the interpretation and modelling. The results of gravity modelling in the southern part of the Porcupine Basin suggest a crustal thickening in the centre of the basin. Comparison with the Rockall Basin, where axial crustal thickening is seismically defined, suggests a similar pattern of crustal extension. The amount of extension is less across the narrower northern sector of the Porcupine Basin, where a north–south-trending axial gravity high is present resulting from anomalous density variations in the lower crust/upper mantle. A new model for the large-scale structural development of the Porcupine Basin is presented that explains the along-axis variations in crustal structure in terms of changes in the kinematics of crustal extension across NW–SE transfer zones. This model involves tectonic unroofing of the mantle lithosphere and serpentinization of the exhumed mantle peridotites.