Structural evolution of the Irish Variscides

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Abstract
The effects of the Variscan orogeny on the Upper Palaeozoic succession are recognizable throughout central and southern Ireland. The deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre-Variscan structures in the basement. The most intense deformation occurs to the south of the Dingle–Dungarvan line, where shortening approaches 50% as a result of layer-parallel shortening, followed by buckling and finally thrusting. The deformation is considered to have developed above a shallow-dipping sole thrust which has been located offshore by the SWAT seismic reflection profiles. Cross-faults, which are common throughout the orogen, resulted from N–S shear couples; this is consistent with their origin as accommodation structures due to differential shortening along strike. The original shape of the Munster Basin has exerted a control on the distribution and overall facing of the major structures. The sole thrust extends to the north of the Dingle–Dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust. The Leinster Massif is considered to be essentially autochthonous; slip on the sole thrust decays towards the Massif which acted as a rigid, passive block and was partially responsible for the arcuate trend of the orogen.