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Department of Geology, University College, Dublin 4, Ireland
Department of Earth Sciences, The University, PO Box 147, Liverpool L69 3BX, UK
Recurrent ductile and brittle displacements characterize the steep boundary mylonite zones that enclose Proterozoic gneisses of the Rosslare Complex in SE Ireland. The northern exposed limit of the Complex is a wide displacement zone containing greenschist facies mylonites derived from two protoliths: (a) basement gneisses and (b) supracrustal metasediments. Important sinistral transcurrent movements produced these mylonites probably during the late Precambrian. Docking of the Precambrian ‘Monian’ sediments to the Rosslare basement may indicate remobilization of a basement/cover relationship. The transpression, uplifted and eroded the mylonites into early Palaeozoic (?Cambrian and Arenig) overstep sediments. Renewed dip-slip displacement, possibly during the Ordovician, was distributed through the mylonites and deformed the sedimentary cover rocks. Finally, the initially wide displacement zone along the northern boundary of the Complex narrowed to discrete brittle faults during subsequent Palaeozoic reactivations. Following pre-Arenig ductile sinistral shear along the probable southern margin of the Complex, each bounding fault strand had divergent histories which involved decoupling of an anastomosing transpressive system.
