METAMORPHISM IN THE CLACHNACUDAINN TERRANE AND IMPLICATIONS FOR TECTONIC SETTING IN THE SOUTHERN OMINECA BELT, CANADIAN CORDILLERA

New and previously published metamorphic data suggest that the Clachna cudainn terrane of the southern Omineca Belt has tectonic affinities w ith the overlying Selkirk allochthon, rather than the underlying Shusw ap metamorphic complex. This interpretation is based on relationships between metamorphic minerals and deformation phases, plutons, and the upper boundary of the terrane, the Standfast Creek fault. Regional kya nite and staurolite zones in the structurally lowest part of the terra ne are overlain by a garnet zone that is continuous upward across the Standfast Creek fault into the Selkirk allochthon. This metamorphism i s inferred to be Jurassic age based mainly on the continuity of these zones with those of known age in the allochthon. Textural relationship s show that metamorphism occurred at different times relative to defor mation across the terrane. Thermobarometry and a petrogenetic grid ind icate that the terrane attained lower to middle amphibolite facies con ditions. Sillimanite and andalusite zones in the contact aureoles of p osttectonic mid-Cretaceous plutons overprint the regional metamorphic zones and the Standfast Creek fault. Comparison of estimated pressures shows that approximately 5-10 km of exhumation occurred between regio nal and contact metamorphism. These metamorphic data are interpreted t o indicate that the Standfast Creek fault had minor displacement after regional metamorphism and negligible displacement after contact metam orphism. Therefore, the fault cannot be an Eocene ductile to ductile-b rittle shear zone that appressed or omitted metamorphic isograds and r apidly exhumed the Clachnacudainn terrane in its footwall, as was prev iously proposed.