Mineral layering in the Galway Granite, Connemara, Eire

Abstract

SUMMARYExamples of semi-horizontal mineral layering in adamellites from the Galway Granite Batholith of Co. Galway, Eire, are described and illustrated. The layering results from variation in the amounts of the constituent minerals in successive horizons of the granite. It is suggested that the layering originated by settling of the early crystallizing minerals during quiescent periods in the emplacement of the granite, and that it may have been much more extensively developed than it is at present. Volatile constituents are thought to have reduced the viscosity of the magma periodically.