In this sector of the Arctic Canadian Shield, mainly high-grade metamorphic rocks of the granulite facies crop out. The regional structural trend is characterized by penetrative foliation, with tight isoclinal folding which produces banding and metamorphic layering of the above lithologies. Generally the banding strikes NE and dips toward the axis of Summit Lake, outlining a wide synform structure. Microstructural relations indicate that the climax of the granulite facies has been reached in anhydrous conditions, and the whole system evolves towards partly hydrated conditions. Geothermometric data calculated from compositions of coexisting mineral pairs indicate T of 750-800 degrees C under inferred P = or <6 kbar. Petrographic and mineral chemistry data indicate that the subsequent metamorphic re-equilibration developed under high-grade amphibolite facies conditions.