Synopsis

A rich assemblage of xenoliths is present in three small Permian dykes that cut the Ross of Mull granite on the SW coast of Mull, bordering the Sound of Iona. The xenoliths, up to 80 mm in diameter, are abundant, and include a wide range of compositions, including spinel lherzolites, dunites, pyroxenites, meta-basic granulite-facies gneisses, anorthosites, anorthoclasites, quartzo-feldspathic gneisses and psammitic meta-sediments. Granitic xenoliths attributable to the Ross of Mull pluton are strikingly scarce. The inference is that the majority of the xenoliths were entrained from beneath the pluton. The xenoliths represent a wide cross-section of the lithosphere, from below the Moho to relatively high crustal levels. Cataclasis and intense shearing in some of the crustal xenoliths suggests that the dykes intersected one or more of the bounding Caledonian thrusts at mid-crustal depths.

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