Potassium–Argon Ages of Slates from the Southern Caledonides of the British Isles

Abstract

THE Caledonian orogenic event in Britain is divisible into a number of episodes of deformation and recrystallization¹. In the low grade Caledonian metamorphic belt (here referred to as the “Southern Caledonides”) which lies to the south of the Scottish Highlands and includes its continuation south-west into Ireland, there is a considerable amount of structural and stratigraphic evidence for the episodic nature of the Caledonian orogeny^2–5. Potassium–argon ages have been obtained from several members of the magmatic sequence in North Wales^6,7, but recent investigations in S.W. England⁸ and in the Scottish Dalradians⁹ have demonstrated the advantages of using whole-rock samples of low grade metamorphic rocks to date episodes of deformation and recrystallization in orogenic belts. This latter approach has now been extended to the Southern Caledonides and the results of a preliminary investigation involving twenty-eight samples are reported here. The analytical data are presented in Table 1 and the geographical distribution of ages is shown in Fig. 1. Details of analytical techniques and precise sample localities are given elsewhere¹⁰.