The southwestern part of the Precambrian Shield of northern Saskatchewan is divisible into five lithostructural domains. The lithological, structural, and metamorphic characters of these domains are described. The Mudjatik and Virgin River domains constitute parts of a more extensive mobile belt extending further east and share a common tectonometamorphic history. The western boundary of this (Hudsonian) mobile belt is marked by the Virgin River shear zone, a zone of repealed movement marked by a narrow belt of mylonite gneisses and sheared marginal granitic intrusions. To the west of the shear zone the Western Granulite and Firebag domains comprise elements of an earlier (Archean?)cratonic foreland, formed by granulite facies gneisses which are only mildly affected by later Hudsonian events. These two cratonic elements are separated by the Clearwater domain, a narrow mobile belt with a history broadly similar to that of the main mobile belt to the east.The Mudjatik and Virgin River domains are formed predominantly by granitoid gneisses, with supracrustal rocks appearing only in thin, often discontinuous zones. It is suggested that these relationships were achieved by remobilization of granitoid (Archean?) basement and preservation of the (Aphebian?) supracrustals between laterally moving, flat lying migmatite nappelobes.

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