Isotopic and geochemical evidence for magma mixing in the petrogenesis of the Coire Uaigneich Granophyre,Isle of Skye,N.W. Scotland

Field relations, petrographic features, major and selected trace element compositions, and Sr- and Pb- isotope characteristics indicate that the Coire Uaigneich Granophyre (CUG) was formed by the mixing of two magmas. One of these, a liquid of high ⁸⁷Sr/⁸⁶Sr ratio (ca. 0.731) formed by the anatexis of late Precambrian Torridonian sediments, contained relict quartz and zircon. The other liquid was an acid differentiate of basaltic magma and was enriched in incompatible elements such as Zr and Y. The two magmas mixed in the proportions of approximately two parts anatectic melt to one part acid differentiate. Hydrothermal metamorphism had no significant effect on the bulk chemistry of the CUG.