A preliminary assessment of low pressure, amphibolite-facies metamorphism in the upper Hyland River area (NTS 105H), southeast Yukon
Description
The regional metamorphic grade in southeast Yukon is low, but amphibolite-facies metamorphism has affected regions adjacent to numerous mid-Cretaceous intrusions. In the upper Hyland River area, contact aureoles approximately 300 m wide are developed around the Hyland and Boundary plutons, which are members of the 97-94 Ma Tungsten plutonic suite. Andalusite + cordierite + biotite-bearing assemblages in the aureole of the Hyland pluton imply emplacement at ~2.5-3 kbar, equivalent to a depth of 9 to 11 km. Cordierite + biotite assemblages in the aureole of the adjacent Boundary pluton suggest emplacement at shallower levels (<~2.5 kbar or <9 km). Metamorphism associated with these intrusions took place after most regional deformation. In contrast, rocks adjacent to the older (ca. 106 Ma) Mount Billings batholith were metamorphosed syn-kinematically. Staurolite ± andalusite ± sillimanite-bearing assemblages in metapelites east of the Mount Billings batholith indicate metamorphism at deeper levels (~4 kbar, or 15 km depth), coincident with the formation of structures oblique to the regional trend.