Influence of basement fabrics on fault reactivation during rifting and inversion: a case study from the Celtic Sea basins, offshore Ireland

Abstract

The evolution of rift basins is often influenced by the reactivation of pre-existing structures, a response that is partly controlled by the angular relationship between fault strike and the subsequent extension/compression axes. In the Celtic Sea basins, offshore Ireland, Caledonian and Variscan structures form a heterogeneous basement for rifting in the Triassic–Jurassic and Cretaceous and for later Pyrenean inversion in the Paleogene. Using 2D and 3D seismic reflection data, we evaluate the impact of a range of pre-existing structures on the style of deformation within basin margin and basin axis settings. The earlier Triassic–Jurassic rift phases arising from NW–SE extension exploited the NNE–SSW-, NE–SW- and ENE–WSW-trending basement structures. By contrast, Cretaceous rifting, with a dominant north–south extension direction, generated newly formed, roughly east–west-trending normal faults, which interacted with pre-existing faults that were only reactivated when they were at >45° to the extension direction. During basin inversion arising from north–south compression, orthogonal extensional faults and highly oblique basement structures were reactivated as reverse and strike/oblique slip faults, and together interacted with the newly formed strike-slip faults. Combining constraints from multiple deformation phases, this study highlights the reactivation response of variably oriented faults to changing extension and compression vectors, and the associated changes in fault behaviour and mode of fault formation. Supplementary material: The location of regional 2D seismic reflection lines and a detailed description of the seismic interpretation are available at https://doi.org/10.6084/m9.figshare.c.6168279