Abstract - Rift basin evolution is often influenced by the reactivation of pre-existing structures, a response that is
partly controlled by the angular relationship of fault strike and 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. Earlier Triassic-Jurassic rift phases arising from NW-SE extension, exploited NNE-SSW,
NE-SW and ENE-WSW trending basement structures. By contrast, Cretaceous rifting, with a
dominant N-S extension direction, generated newly formed, approximately E-W 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 N-S compression, orthogonal extensional
faults and highly oblique basement structures were reactivated as reverse and strike/oblique-slip
faults, and together interacted with 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.
Journal of Geological Society London, 180, doi: https://doi.org/10.1144/jgs2022-024, 2022.