Mississippian U-Pb dates from Dorsey Terrane assemblages in the upper Swift River area, southern Yukon Territory

The polydeformed Yukon–Tanana terrane in the southwestern half of the Wolf Lake map area (NTS 105 B) includes the Big Salmon Complex and Dorsey Terrane, which has been divided into four assemblages: Ram Creek, Dorsey, Klinkit, and Swift River. Zircons in a granodiorite in the mostly metavolcanic Ram Creek assemblage are broadly Early Mississippian — a signature age for Yukon–Tanana terrane intrusions. Zircons from a metatuff horizon within the dominantly siliciclastic Dorsey assemblage are 355 ±2.7 Ma, which is similar to some dates from the Finlayson Lake belt (Money Creek thrust sheet), but older than dated volcanic rocks in the Big Salmon Complex (330–325 Ma). The greater age, continental derivation, and metamorphic grade of the Dorsey assemblage suggest that these rocks were both basement and some of the earliest products of the Mississippian arc assemblage that comprises much of the southern Yukon–Tanana terrane. 2001-A1 C.F. Roots and L. Heaman 1 CURRENT RESEARCH RECHERCHES EN COURS 2001 Article Article Titles Titres Purchase Information Information pour acheter 1 Contribution to the Ancient Pacific Margin NATMAP Project. 2 Yukon Geology Program, 2099 2nd Avenue, Whitehorse, Yukon Territory Y1A 3P3 3 Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta T6G 2E3