PALEOGEOGRAPHY AND TECTONIC EVOLUTION OF PALEOZOIC STRATA OF THE NORTHERN KOOTENAY ARC, SOUTHEASTERN BRITISH COLUMBIA

New field studies and detrital zircon geochronology from the lower Paleozoic Lardeau Group and Carboniferous Milford Group south of the TransCanada Highway at Revelstoke, B.C. have tightened constraints on the Paleozoic evolution of the southern Canadian Cordillera. As first reported by J.O. Wheeler in 1968, the Lardeau Group was buried, deformed ductilely, and exhumed prior to deposition of the Upper Mississippian Milford Group. The cause of the deformation has remained enigmatic. A newly recognized sequence of phyllite, grit and limestone that unconformably underlies the Milford Group but post-dates the Paleozoic deformation event has locally been preserved. The new sequence is inferred to be of Upper Devonian or Lower Mississippian age and may correlate with strata to the east or west. Carboniferous and Permian rocks assigned to the oceanic Slide Mountain terrane are in depositional contact with the Lardeau Group north of Trout Lake, confirming the earlier interpretation that the strata represent a marginal basin stratigraphically linked to North America. Detrital zircon samples from the area possess two distinct patterns: one mimicking the pre-1.7 Ga Alberta basement, and the other containing an additional abundance of Mesoproterozoic grains aged ca. 1.5 Ga and ca. 1.3-1.0 Ga. Potential sources of the Grenville-aged detrital zircon in the southern Canadian Cordillera may exist nearby, and new constraints for paleogeographic models can be outlined in light of the data.