Thermobarometric Constraints on Mid-Cretaceous to Late Cretaceous Metamorphic Events in the Western Metamorphic Belt of the Coast Mountains Complex near

The western metamorphic belt is part of the Coast Mountains Complex of southeastern Alaska and western Canada. This complex formed as a result of mid-Cretaceous through middle Eocene crustal shortening between the previously amalgamated Wrangellia and Alexander terranes (Insular superterrane) and previously accreted terranes of the North American continental margin (Intermontane superterrane). The western metamorphic belt, which ranges from a few kilometers to several tens of kilometers in width, records a complex sequence of contact-metamorphic and regional metamorphic events, the most significant of which are designated M1 R , M2 C–R , and M3 R . The M1 R regional metamorphic event ranged in grade from subgreenschist to greenschist facies and was overprinted by the M2 C–R and M3 R metamorphic events. The M2 C–R metamorphic event is recorded in discrete contact-metamorphic aureoles and regional metamorphic-mineral assemblages related to tonalite-granodiorite plutons of the Admiralty-Revillagigedo plutonic belt. The M3 R metamorphic belt, which is adjacent to the M2 C–R belt, is characterized by regional Barrovian isograds of garnet, staurolite, kyanite, and sillimanite. Using the THERMOCALC program, pressure-temperature (P–T) conditions for the M2 C–R metamorphic event are estimated to be in the ranges 5.3–7.5 kbars and 525–640oC and for the M3 R metamorphic event in the ranges 9.4–12.6 kbars and 730–895oC. The M2 C–R