Abstract - The Cenozoic tectonics of North West Europe is generally attributed to a combination of three major controls: Alpine compression, mantle plume-related uplift and North Atlantic opening. The relative influence of each is the subject of ongoing debate. North East Ireland hosts extensive exposures of Paleogene rocks of the North Atlantic Igneous Province and in combination with a number of high resolution geophysical data sets, provides a firm basis for considering the contribution of each factor. Evidence derived from analysis of the Tellus aeromagnetic dataset suggests that North East Ireland was subjected to N-S Alpine compression resulting in strike-slip faulting, which was punctuated by plume-related NE-SW to ENE-WNW extension. The latter is reflected in the considerable numbers of associated WNW-NW trending dykes which have been revealed by the aeromagnetic survey and are age constrained by cross-cutting relationships with stratigraphic units, intrusions or faults. Four distinct swarms show different amounts of lateral displacement across NE-SW trending sinistral strike-slip faults, attesting to the broadly overlapping periods of extension and faulting. Strike-slip faulting conforms to conjugate pairs of NE-trending sinistral and NNW-trending dextral faults, with displacements of up to 2.5km. Sinistral faults reactivate pre-existing Caledonian and Carboniferous structures, whilst dextral faults show no evidence of previous structure. NNW-trending dextral faults mapped from seismic data farther to the south in the Irish Sea are believed to be the lateral equivalent of onshore structures which extend into the Lough Neagh Basin. The latter is characterised by thick sequences of both Oligocene clays and earlier Palaeocene basalts, and appears to represent a pull-apart basin which is close to the intersection of major dextral and sinistral strike-slip faults. Evidence therefore indicates that, during the Cenozoic, North East Ireland was tectonically controlled by a background N-S Alpine compression which was periodically overwhelmed by well-defined phases of plume-related rifting and associated volcanic emplacement.
Abstract of poster presented to:
Tectonic Studies Group Annual Meeting, Birmingham, January 2010.