MULTI-STAGE THERMAL EVOLUTION OF THE HYLAND RIVER METAMORPHIC COMPLEX IN SOUTHEAST YUKON, CANADA

The upper Hyland River area, located in southeast Yukon, Canada, is characterized by Neoproterozoic – Cambrian metasedimentary rocks of the Selwyn Basin. Rocks in this area underwent low-grade regional metamorphism during the Jurassic-Cretaceous and are overprinted by a later medium- to high-grade stage. In the field, the metamorphic complex has been mapped as a series of semi-concentric metamorphic zones. These zones are cut by a series of mid-Cretaceous granitic intrusions, including the Hyland River suite (ca. 105-100 Ma) and the Tay River and Tungsten suites (ca. 99-95 Ma).

This study focusses on constraining the tectono-metamorphic history of the Hyland metamorphic complex using P-T pseudosection modelling linked with LA-ICPMS garnet mapping to better understand the thermal evolution of these rocks, and its association with emplacement of the Cretaceous plutons.

Results from structural analysis and phase-equilibria modelling indicate the phyllites that host the intrusive rocks are overprinted by two metamorphic stages. The first metamorphic event occurred at medium pressure (~0.5-0.6 GPa) and temperatures ranging from 400°C to 850°C with the highest temperatures associated with abundant partial melting being recorded in the core of the metamorphic complex. This metamorphic stage records a complex history of growth and resorption garnet which occur both under sub- and supra-solidus conditions. The second metamorphic stage is characterized by growth of andalusite and its replacement by sillimanite at <0.3 GPa. These two metamorphic events can either be interpreted as a single metamorphic cycle associated with exhumation or two distinct tectono-metamorphic events.

Constraints on the timing of metamorphism are being undertaken to better understand the P-T-t evolution of these rocks and the relationship to Cretaceous plutonism and emplacement of Au-bearing quartz-calcite veins in the region.