XIII.—Granites and Associated Rocks of the Eastern Part of the Western Redhills Complex, Isle of Skye

Abstract

SynopsisThe country lying between the head of Loch Ainort and the northern end of the Blaven Range in central Skye forms part of a Tertiary igneous complex. Country rocks in the area are Jurassic sediments. The earliest igneous rocks are basalt lavas which show the effects of thermal metamorphism by a later intrusion of eucrite and gabbro. This latter, which is part of the Blaven mass, has features of a layered intrusion such as igneous lamination, repetition of layers rich in certain minerals and comparable textures. It may be correlated with zones of the Cuillin layered intrusion. The eucrites are cut by a cone sheet swarm. Adjacent to the eucrite is a vent breccia which contains eucrite blocks, is not cut by cone sheets and is, therefore, of later age than the eucrite. The major part of the area under discussion is formed from four granitic ring dykes and a hybrid suite with ring dyke form, all of which belong to the Western Redhills intrusive complex; in addition, part of a fifth granitic ring dyke, which probably belongs to the Eastern Redhills intrusive complex is included in the area. The granites are mainly fayalite-hedenbergite types with a variety of phenocrysts of felspar and features characteristic of high level intrusions such as granophyric texture and varying optical and chemical properties of the felspar indicating higher temperature modifications. Three new chemical analyses of the granites and one of ferrohedenbergitic pyroxene are presented. The granites may be regarded as partial remelts of the underlying basement gneiss and a simple investigation of thermal requirements indicates that the heat necessary for the partial melting could be provided by a mass of basic rock presumed from geophysical evidence to underlie the complex. Various acid and basic minor intrusions in the area are also described.