The Central and South-West Highland Epidiorites: A Study in Progressive Metamorphism

Abstract

I. Introduction Ever since the publication of Teall's description of the Scourie dyke (1885, p. 133) and its passage from a dolerite into a foliated amphibolite by the ordinary processes of metamorphism, petrologists have from time to time directed their researches along modern lines to a study of the metamorphism of basic igneous rocks. No formal review of the literature is necessary owing to the numerous references contained in the following pages, but among the earlier writers Maculloch (1821, p. 298), De la Beche (1834, pp. 298 et seq.) and Sterry Hunt (1875) may be mentioned. Although frequently the work of these authors was a model of careful observation and accurate description, their inference that hornblendic rocks were chemical precipitates from a thermal ocean can to-day be regarded as of historical interest only. It was thus left for Jukes (1862, pp. 169–72) to suggest that many hornblendic rocks were altered lavas or tuffs. Dealing with amphibblites chiefly from the south-west of England, Allport (1876, p. 422), Phillips(1876, p. 155,and 1878, p.471), and Bonney (1883, p. 14) expressed the opinion that they were metamorphosed igneous rocks. Shortly afterwards, the Scottish Geological Survey (Geikie, 1884, p. 122) in the course of their investigations on the amphibolites of Aberdeenshire and Banffshire came to a similar conclusion. Lehmann (1884, p. 190) also arrived at this conclusion for the amphibolites from the Saxon Granulitgebirge, when describing the passage of a gabbro into a schistose amphibolite, whilst Lessen (1882–3) studied the contact metamorphism of a diabase