Metamorphism around the Ross of Mull Granite

Abstract

I. T he G ranite and the M oine G neisses . ( a ) The Granite. T he western end of the Ross of Mull, which stretches out into the Atlantic, is a granite mass occupying some 20 square miles of land. On the north, west, and south this granite is exposed to the ocean waves, but along its eastern border it is seen in contact with a series of typical Moine Schists, which form the next portion of this peninsula passing landwards. The Ross of Mull granite is a muscovite-biotite-granite of coarse texture intruded into the Moine Schists and Gneisses. At the south-western corner of the Ross, opposite the island of Erraid, it gives place to a fairly coarse diorite, which also forms the Eilean a' Chalmain. The granite was intruded probably before the diorite was cool, and the two rocks are there so intermixed that the drawing of any boundary-line between them is a purely arbitrary matter. Taken together, the facts summarized below lead to the conclusion that this granite is one of the ‘Newer Granites,’ as was formerly inferred by Prof. Judd:— ( a ) It resembles the newer granites in composition and association with diorite. ( b ) It is unaffected by shearing. ( c ) It is conspicuously later than the foliation and strain-slipping of the Moine Schists into which it has been intruded, producing contact-alteration. ( d ) It is associated with sheets of mica-trap and vogesite, by which it is traversed. In one case, an intrusive sheet