Relationship between metamorphism and migmatization in the northern part of the Moine Nappe

Synopsis It is shown that in northern Scotland there is a regional decrease in metamorphic grade westwards from the migmatites of central Sutherland towards the Moine thrust belt. Regional structural and microfabric evidence demonstrate that migmatization was coeval with the climax of regional metamorphism. The migmatites have a sheet-like form and overlie unmigmatized rocks. Thermal surfaces in the unmigmatized rocks are geometrically related to the base of the migmatite sheet and are inverted. It is concluded that the heat source immediately responsible for the thermal structure lay in the migmatites themselves.