The late Mesozoic and Cenozoic metamorphic evolution of the western North American continental margin is recorded in a belt
of homogeneous metapelitic rocks, the Kluane metamorphic assemblage (KMA), in the northern Coast Belt of Yukon Territory.
A record of Late Cretaceous medium-pressure and -temperature (~7kbar, 500°C) metamorphism, M1, is preserved in Ca-rich
garnet and Na-rich plagioclase cores in rocks that were little affected by later events. M1 was synchronous with
mylonitization and is attributed to accretion of the KMA to the ancient continental margin. Isothermal decompression
during rapid uplift was followed by Early Eocene emplacement of the Ruby Range Batholith (RRB), part of a magmatic arc
produced by subduction of the Kula plate. The intrusion of the RRB led to a contact metamorphic overprint, M2, producing
a 5 to 6km wide aureole in which grade ranges from sub-garnet zone to garnet-cordierite-K-feldspar zone. Pressure and
temperature estimates for M2, calculated from mineral equilibria are 3.5-4.5kbar and 530 to 720°C, generally consistent
with stability limits of observed mineral assemblages. Comparison of mineral assemblages and P-T conditions in the KMA
with those in the Mclaren Glacier metamorphic belt in Alaska does not support correlation of the two metamorphic sequences.
This weakens the hypothesis proposing 400km of dextral slip along the Denali fault zone.
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