Abstract

Dr. M. D. Max and Mr. C. B. Long write: The crystallization age of the Slieve Gamph Igneous Complex has been determined by Pankhurst et al. 1976, using the Rb/Sr whole rock isochron, at c. 487 ± 6 Ma, with an age of 494 ± 9 Ma for the Ox Mountains Granodiorite, which is the oldest major body in the complex. This is consistent with a 500 ± 18 Ma age determined by the same method (Max et al. 1976) to determine the earliest age of crystallization. However, the main geological conclusion (Pankhurst et al. 1976) that the age of the granodiorite can be used to infer a pre-Caledonian age (see also Phillips et al. 1975) for the metasedimentary envelope may be misleading, and we propose that the envelope rocks have not yet been shown to have other than a Caledonian tectono-thermal history.

Although the sedimentary age of the Ox Mountains succession is subject to interpretation (Long 1974,, 1975, Long & Max, 1977 Phillips et al. 1975) there appears to be unanimity about the metamorphic and structural state of the Ox Mountains succession during emplacement of the granodiorite. Long (1975) and Long & Max (in press) regard it as having been at almandine amphibolite facies; Taylor (1966) was of similar opinion, and Phillips et al. 1975 also regarded it as having been at amphibolite facies. Pankhurst et al. (1976, p. 328) concluded that the granodiorite was deformed at moderate to high P-T conditions, which may imply similar conditions in the

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