Abstract -
The Tellus aeromagnetic dataset suggests the existence of a conjugate strike-slip fault system in Northern Ireland from the Palaeogene through to the Oligocene times. Kilometre scale displacements are observed along two dominant trends, with NNW-SSE trending dextral faults offsetting igneous complexes in the east, and with NE-SW sinistral faults reactivating older Carboniferous and Caledonian structures and displacing broadly contemporaneous Palaeogene dykes. This structural configuration is supported by interpretation of 2D and 3D seismic datasets further to the south within the Irish Sea, with the NNW-SSE trending Codling Fault accommodating km-scale dextral displacements and representing the lateral equivalent of similar structures, referred to as the Newry and Camlough Faults, observed onshore. This strike-slip fault system has been attributed to Alpine-related N-S regional shortening.
Detailed mapping of both onshore and offshore faults has highlighted the presence of a variety of associated accommodation structures along their length. The Codling fault is characterised by arrays of minor riedel strike-slip faults and by the presence of pull-apart basins, as expected, along right-stepping bends. Similarly onshore accumulations of Oligocene sediment are associated with left-stepping bends along the NE-SW striking sinistral Tow Valley fault. Combined with evidence suggesting that igneous complexes could be spatially associated with, and perhaps even controlled by, the Newry/Camlough faults, there are strong grounds for suggesting that strike-slip faults are accompanied by associated volumetric strains which localise both sedimentation and igneous activity. Potentially the most profound impact of this fault system is seen, however, in the Lough Neagh area where the principal strike-slip conjugate faults intersect and the thickest accumulations of both Palaeogene basalts and Oligocene sediments are found. This structural configuration is attributed to right stepping of major dextral strike-slip fault across a reactivated sinistral strike-slip fault, leading to stretching which is coincident with the conjugate fault intersection and the related pull-apart.
Abstract of talk presented at:
Atlantic Ireland Conference, Petroleum Affairs Division, Dublin, October 2011.