MANTLE DYNAMICS AND GEOTHERMAL ENERGY POTENTIAL OF THE SOUTHERN CANADIAN CORDILLERA: CONSTRAINTS FROM SEISMIC AND MAGNETOTELLURIC DATA

The southern Canadian Cordillera is a modern mobile belt that extends ~500 km eastward from the active Cascadia volcanic arc to the Rocky Mountain Trench (RMT). In recent years, there has been increased interest in the geothermal energy potential of this area, owing to its regionally high surface heat flow (>70 mW/m²) and local areas of ongoing volcanic activity. The high crustal temperatures are largely related to the underlying mantle dynamics of this region. In this study, we present an updated assessment of the thermal structure of the shallow Cordillera mantle (50-200 km depth) using two independent data sets: 1) shear wave velocities from seismic tomography model NA07, and 2) long period magnetotelluric data. On a regional scale, the Cordillera mantle is characterized by low shear wave velocities (>4% slower than average mantle) and low electrical resistivity (<100 Ωm). Using mineral physics relationships, we invert each data set to create maps of mantle temperature, water content and melt fraction. Both data sets are consistent with near-adiabatic mantle temperatures (>1300°C) below 60 km depth and a partially hydrated mantle throughout the Cordillera. In some areas, such as the boundary between the Intermontane and Omineca Belts, the observed Vs and electrical resistivity are too low to be explained only by temperature and hydration, suggesting that partial melt may be present. Fluid content appears to decrease eastward across the Omineca Belt, and there is a transition to cooler and relatively dry mantle at the RMT. Overall, the geophysical observations indicate a hot, thin lithosphere across the width of the Cordillera. The high temperatures are interpreted to be the result of vigorous convection of mantle that has been hydrated over the long history of subduction below western Canada. Further, mantle convection maintains high temperatures in the deep crust (>800°C at 35 km depth), making this a region of high geothermal energy potential.