THE SOUTHERN MOUNTAINS IGNEOUS COMPLEX, ISLE OF RHUM

Abstract

The structure and petrology of an acid complex forming the southern part of the Rhum Tertiary igneous centre are described. The rock types of primary concern are felsites, explosion breccias, intrusive tufts and granophyre. The intrusive rocks have been injected along an arcuate fracture, 1½ miles in diameter, with subsidence of country rock centrally. The order of intrusion has been, first felsites associated with explosion breccias, followed by intrusive tufts, and finally granophyre. These three phases mark increasing depths of formation. It is concluded that the explosion breccias and intrusive tufts had their origin in the escape of water vapour from porphyritic acid magma that subsequently crystallized as felsite, and that the granophyre is the crystallization product of an apparently identical magma which retained its water content.