Abstract

High-grade metasedimentary rocks, probably of both early Paleozoic and late Paleozoic – Triassic ages, underlie an area termed the Nemo Lakes belt between Slocan and Arrow Lakes in the northern Valhalla Range, southeastern British Columbia. The rocks have experienced two possibly related periods of major folding. Phase 1, accompanied and outlasted by metamorphism at PT conditions of 5.0–6.8 kbar (500–680 MPa) and 630–680 °C, involved emplacement of ultramafic rocks, major faulting, and folding. Phase 2 involved large-scale inclined to upright folds which were dominantly south-verging, deforming the phase 1 fabric. Both phases probably occurred in the Middle to Late Jurassic, as part of the Columbian Orogeny.Rocks lithologically and structurally similar to those of the Nemo Lakes belt are found across the Rodd Creek fault near the Columbia River and extend the general continuity of the belt into the Shuswap metamorphic complex.Plutonic rocks, some of which bracket the movement on the Rodd Creek fault, the southern extension of the Columbia River fault zone, range in age from Middle Jurassic to EoceneIn the valley of Slocan Lake, a major normal fault is postulated on structural and metamorphic grounds and may be related to the north–south arching of the Valhalla gneiss complex. It is suggested that this arching and uplift, which followed phase 2 deformation, produced both the fault and a zone of cataclasis on the eastern side of the complex, and gave rise to its domal shape.

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