Structural history and plutonic and metamorphic geology of the Central Southern Indian Lake Area, Manitoba
Frohlinger, T. G.
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This study of the plutonic, metamorphic and structural history of the Central Southern Indian Lake area consisted of field mapping followed by petrographic, structural and chemical analyses. The mapping of the 1000 square mile map-area was at a scale of 1/2 mile = 1 inch, while areas of greater structural and lithographic complexity were mapped at two times this scale. All consolidated rocks in the map-area are Precambrian in age, and most exhibit regional metamorphism to the amphibolite facies. Wasekwan-type gneisses and migmatites derived from greywacke, and the later, Sickle-type gneisses and migmatites, derived primarily from arkose, are separated by post-Wasekwan-type basic igneous rocks of intermediate age. The Sickle-type gneisses were subsequently intruded by basic igneous rocks and then by granitic intrusions. Pegmatites and aplites intrude most units but their relative age is uncertain. Lamprophyre and diabase are the youngest rocks in the area through neither forms mappable bodies. The area has undergone two, and possibly three, events of prograde regional metamorphism, plus localized retrograde development of chlorite epidote associate with shearing (late-tectonic D4). The first event (M1), amphibolite facies, is found effecting only the Wasekwan-type gneisses. There is indirect evidence for a second event (M2), effecting only Wasekwan rocks (pre-Sickle). The third event (M3), amphibolite facies but with lower temperatures than M1, effects Wasekwan and Sickle rocks...