Potassium–Argon Ages of some Aberdeenshire Granites and Gabbros

Abstract

POTASSIUM–ARGON age determinations have been made on specimens of granites and gabbros representative of the ‘younger’ Caledonian plutonic intrusions of north-east Scotland. Unlike the ‘older’ igneous rocks these ‘younger’ intrusions post-date the earlier fold movements and acme of regional metamorphism in the Dalradian schists1. The exact relation of the gabbro intrusions to the established sequence of movements and metamorphisms in the Dalradian rocks has received considerable attention2–6. It is evident that their emplacement post-dated the large recumbent (F1) fold structures of north-east Scotland (Banff Nappe), the second phase (F2) structures and the static (post-F2) climax of regional metamorphism; also the evidence strongly favours deformation of the gabbros by the Boyndie–Buchan group of folds (F3) and is suggestive of their intrusion as a single large sheet2.