Stepwise Decay of Rift Propagation in the Porcupine Basin, Offshore West of Ireland

The influence of transversal crustal discontinuities on the development of continental rift systems remains poorly constrained, especially because their connection with shallow normal faults is often unclear. Nonetheless, these basement faults likely affect the dynamics and the kinematics of the rifting, especially during the early stages of extension. Our study focusses on the Porcupine Basin, offshore west of Ireland, an aborted rift propagator that experienced a 220 Myr-long geological evolution with several rifting episodes. Detailed seismic analysis, integrated with exploration well data, illustrates the regional complexity of the structural patterns across the basin, with faults running subparallel or transverse to its axis. This tectonic framework controlled the northward migration of the crustal stretching during the Late Jurassic, followed by crustal thinning during the Early Cretaceous. Pre-existing, orogenic-derived structures bound crustal terranes that control deformation pulses when rifted apart. This suggests structural barriers that either slowed the northward rifting migration during the Oxfordian, Kimmeridgian and Tithonian when crosscutting through the Variscan and Caledonian fold-and-thrust belts, or stopped the rifting by the end of the Barremian when it encountered Caledonian and Grenvillian crystalline basements. We propose that this structural inheritance led to the formation of a typical rift propagator of continental nature, and that the Porcupine Basin constitutes a remarkable example of a termination of rifting processes in a well-formed oceanic rift system.