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. Orogen-normal 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 strike-slip 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.