Tectono-Metamorphic Evolution of the Snowcap Assemblage, Yukon-Tanana Terrane, West-Central Yukon

Quantitative and qualitative analyses of Snowcap Assemblage metapelitic rocks of the Yukon-Tanana terrane (YTT) in west-central Yukon results in the identification of three phases of metamorphism and deformation through garnet crystallization modeling coupled with garnet age dating. A first Permo-Triassic metamorphic event (ca. 245 Ma), associated with a heating event occurring during the emplacement of Permian granitoids, reached low P amphibolite facies metamorphic conditions. The second metamorphic event dated at the Jurassic (ca. 197-188 Ma) reached peak P-T conditions of 7 kbar and 650-685 °C with a heating rate of 20 °C/My and is followed by a dwell period at T > 600 °C. This event follows typical Barrovian-type metamorphism and is interpreted to be associated with the accretion of the YTT onto Laurentia. The third metamorphic event, post-Jurassic in age, reached peak P-T conditions of 6 kbar and 580 °C with a heating rate of 20 °C/My.