Lough Neagh : the site of a Cenozoic pull-apart basin

The Lough Neagh Basin in Northern Ireland is the site of a Cenozoic depocentre defined by gravity measurements and a thick succession of Paleocene basaltic lavas and Upper Oligocene clays. Much of the Cenozoic outcrop is concealed by Lough Neagh, but the rhombic outline of the lough provides some indication of the underlying structural control of the depocentre. Several authors have inferred that a Cenozoic pull-apart basin lies within the Lough Neagh area and suggest it is one of a number of transtensional basins, including the Bovey and Petrockstow basins in SW England, associated with NW to NNW-trending strike-slip fault zones. Solid geology maps and gravity data show that the structure of the Lough Neagh Basin is dominated by a segmented, orthogonal pattern of offset NNW and NE-trending faults. It is proposed that pull-apart basin formation took place in the Mid-Paleocene by dextral movement on these offset faults. The potential link between strike-slip tectonics and Cenozoic volcanism in the north of Ireland is briefly considered.