Structure, geochronology and thermobarometry of the eastern flank of the Shuswap metamorphic complex in the Upper Arrow Lake area, southeastern British Columbia

The Upper Arrow Lake - Trout lake area can be described in terms of suprastructure, infrastructure, and transition zone. The suprastructure comprises phyllite and schist of the biotite to garnet zone, which preserve Mesozoic deformation and cooling ages. It is marked by brittle structures and moderately to steeply dipping axial surfaces. The infrastructure includes amphibolite-facies metasedimentary rocks, which record Late Cretaceous to Paleocene peak metamorphic assemblages. The infrastructure features intensely transposed foliation, a strong stretching lineation and evidence of non-coaxial deformation. The transition zone is defined as a thin crustal section characterized by a steep, yet continuous metamorphic gradient. New thermobarometric data indicate that the transition zone underwent staurolite to sillimanite zone metamorphism; LA-ICP-MS and CHIME dating of monazite suggests that the transition zone experienced a thermal event between 81 and 87 Ma.; The Upper Arrow Lake - Trout Lake area has been interpreted to encompass the transition between autochthonous continental strata, and outboard and accreted terranes of uncertain paleogeographic position. A U-Pb detrital zircon study with LA-ICP-MS was undertaken in Proterozoic schist and gneiss of the Monashee complex cover succession and the mid-Paleozoic Chase Formation to try to elucidate the provenance of these units. This study shows that the analyzed units are dominated by zircons derived from multiple sources along the western Canadian Cordilleran margin, but ultimately derived from North America. The investigated Proterozoic and Paleozoic strata demonstrate sedimentologic and depositional relationships with respect to ancestral North America, and as such, are interpreted to represent outboard extensions of the Cordilleran miogeoclinal succession.; This study proposes a revised tectonic evolution of the eastern margin of the Shuswap metamorphic complex whereby east-directed translation of the suprastructure and infrastructure upon the Monashee complex was accommodated via mid-crustal flow above an inherited, relatively stiff ramp. Destabilization of the crust triggered lateral spreading; east-directed shearing within the infrastructure accommodated gravitational spreading, whereas brittle normal faulting was mostly limited to the suprastructure and transition zone.