Abstract

On the basis of K/Ar determination on biotite, the granite of the Mourne mountains, Ireland, has an age of 75 + or - 7 million years, or early Tertiary. The granite and the Tardree rhyolite have, at one time, been considered as belonging to the same period, that is, intermediate between lower and upper basalts of the region. Chemical dissimilarity discounts this idea, and in addition a late Miocene or early Pliocene age (not more than 23 m.y.) recently proposed for the Interbasaltic Bed, plus the age evidence for the granite, confirms the lack of direct relationship of the granite and the rhyolite. In the discussion by Le Bas, existing age data are summarized and it is pointed out that present data show the Mourne and Carlingford complexes to be the same age and the Carlingford granophyres to be later than the Carlingford lavas. In the discussion by Harland the lower Tertiary age of the main Thulean igneous activity in Scotland is maintained.

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