| Summary: | The early Tertiary marked a period of intense magmatic activity in the Canadian Cordillera as a consequence of tectonic restructuring within the Kula-North American plate system from orthogonal to oblique convergence. Resultant calc-alkaline volcanism formed a discontinuous belt (Challis Arc) along the eastern margin of the Coast Plutonic Complex (CPC) from south-eastern Alaska through Yukon into west-central British Columbia and northern Washington State. The Sifton Range volcanic complex (SRVC) is the Yukon's largest Paleogene erosional remnant of volcanic rocks (240 km2), and represents the only coeval volcanic-plutonic suite within the Sloko-Skukum Group of southern Yukon Territory and northern British Columbia. It comprises a 900-m thick, shallow-dipping, volcanic succession dominated by intermediate to evolved lavas and abundant felsic pyroclastics deposited in a north-westerly trending half-graben. Three volcano-stratigraphic units are documented: (1) Lower Interbedded Unit, (2) Middle lavas, and (3) Upper Interbedded Unit. Locally, the volcanic sequence is intruded by biotite, hornblende, two-feldspar granites of the CPC's Nisling plutonic suite dated at 57.5 Ma. Felsite sills radiate from the main intrusive body, and together with numerous basaltic to dacitic dykes traverse the entire volcanic package. (Abstract shortened by UMI.)
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