Evolution of the Coast Cascade Orogen by Tectonic Thickening and Magmatic Loading: The Cretaceous Breakenridge Complex, Southwestern British Columbia

A model for the tectono-magmatic mid-Cretaceous (110--80 Ma) evolution of the southern Coast belt is proposed. The first magma pulse represented by the 107--100 Ma Breakenridge pluton intruded within a magmatic arc as a set of shallow sills. It was initially buried by orogen-parallel contraction, followed by the emplacement of the 96-94 Ma Snowshoe pluton, which belongs to the second magma pulse. The Snowshoe pluton was emplaced by similar mechanisms in structurally higher levels of the crust. Orogennormal compression was the final mechanism for deep burial and attainment of peak metamorphic conditions (500--680°C at 6.5--10.3 kbar) of the study area between 91--86 Ma. Following orogen-normal contraction and regional folding, oblique right-lateral strikeslip shearing occurred while rocks were in a ductile environment. The third magma pulse (86--84 Ma) was synchronous with the late stages of high-grade metamorphism and early stages of oblique strike-slip movement.;Keywords: Canadian Cordillera; Coast Plutonic complex; pluton emplacement; regional accretion; LA-ICPMS geochronology; geothermobarometry.