Late Cretaceous to Paleogene tectonometamorphic evolution of the Shuswap Metamorphic Complex, British Columbia

The Shuswap Metamorphic Complex (SMC) in southeastern British Columbia exposes penetratively deformed rocks exhumed from the deepest structural levels of the Canadian Cordillera. U-Th-Pb monazite petrochronology, metamorphic phase modelling and microstructural analysis are used to quantify Pressure-Temperature-time-deformation (P-T-t-d) constraints on deep orogenic processes and the activity of ductile shear zones bounding the SMC. Dates obtained from monazite chemical domains, correlated with metamorphic and deformational fabric-forming events, suggest that peak metamorphic conditions young with increased structural depth, and reflect a progressive localization of opposite-sense shearing towards the top and bottom margins of the SMC over time. Protracted northeast-directed compression occurred from ~165–58 Ma, after which west-directed ductile extension continued until at least ca. 47 Ma. P-T-t-d paths are consistent with basal accretion in front of a foreland-propagating ductile thrust system, followed by exhumation via normal faulting – similar to models proposed for other collisional systems such as the Himalayan orogen.