The status of the Banff nappe

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Abstract
Summary: The status of the major horizon of gneisses (Cowhythe, Donside, Ellon and Inzie Head gneisses) in NE Scotland has been reinterpreted, on the basis of geochronological and fabric evidence, as the basal element of a major nappe, the Banff nappe. It is suggested that these gneisses represent a pre-Caledonian basement gneiss-complex, thrust into its present structural position during the Grampian phase of the Caledonian orogeny, after the formation of the Tay nappe. The basal zone of this unit is characterised by the development of distinctive mylonitic assemblages. In this interpretation, the rocks of the overlying Banff division form part of the allochthonous assemblage, as a Caledonian cover sequence, uncoupled from the basement along the Boyne line during emplacement.