CARBONIFEROUS SUBVOLCANIC ACTIVITY ON THE BEARA PENINSULA, SW IRELAND

Magmatic activity associated with the Munster Basin has been more wide spread than previously reported. The Munster Basin is a substantial se dimentary basin, and towards the end of its extensional phase of devel opment, at the beginning of the Variscan orogeny in Ireland, numerous intrusions were emplaced into consolidated Upper Devonian and Lower Ca rboniferous sediments on the Beara Peninsula. One hundred and sixty-fo ur sills and dykes have been mapped which are subalkaline to alkaline in nature. Two separate suites have been identified. The northern suit e comprises subalkaline basalts of God's Head and Dursey Island which are intruded into Devonian Red Beds, and the southern suite comprises alkali basalts, trachytes and phonolites which crop out along 9 km of the south coast of the Beara Peninsula and are suggested as Brigantian in age. They are intruded into Devonian Red Beds and marine Lower Car boniferous strata and are therefore later than the tholeiitic magmatis m on the Iveragh peninsula to the north. The alkaline magmatism on Bea ra was induced by lithospheric thinning and controlled partly by pre-e xisting zones of weakness in the Caledonide crust and partly by fractu re zones that developed parallel to the Munster Basin margin as it sub sided. In contrast to the Iveragh Peninsula, the stretching factor for the Beara lithosphere was never large enough to lead to the productio n of tholeiitic magmas. (C) 1997 John Wiley & Sons, Ltd.