Abstract

Ultrabasic and basic gneiss masses exposed in the early Lewisian (Precambrian) complex, near Scourie and Drumbeg, Sutherland, Scotland, have been defined as metamorphosed and disrupted layered igneous intrusions. This interpretation is considered incompatible with the field relationships, mineralogy, and geochemistry of the rocks. A modified version of the hypothesis that the ultrabasic and basic gneisses are metamorphosed intrusive sill-like masses within a migmatite complex now represented by the layered acid gneiss is proposed, incorporating the concept that the ultrabasic gneisses represent ultrabasic intrusive rocks which were tectonically emplaced among rocks that subsequently became the layered acid gneisses.

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