STRUCTURAL AND NEOTECTONIC CONTROLS ON HYDROTHERMAL UPWELLINGS IN THE SOUTHEASTERN CANADIAN CORDILLERA

Thermal springs in the Canadian Cordillera are spatially associated with regional-scale faults, which likely act as conduits for ascending thermal fluid. The specific structural and tectonic conditions that localize spring outlets along these faults are not well understood. Here, we present new data from detailed structural mapping along the Columbia River, Purcell Trench, and Southern Rocky Mountain Trench faults in the southeastern Canadian Cordillera. These faults were historically regarded as Eocene normal faults. However, our dataset of nearly 700 kinematic indicators, as well as the observation of several cross-cutting relationships and piercing-point offsets, indicate a younger, post-Eocene phase of dextral slip. Furthermore, the focal mechanisms of small (< M5) crustal earthquakes in the study area are dominantly strike-slip, with dextral nodal planes oriented subparallel to the strikes of the Columba River, Purcell Trench, and Southern Rocky Mountain Trench faults. This correlation suggests that dextral strain is currently being accommodated on these faults, which is key to understanding the localization of active hydrothermal systems along them. Placed in the context of ongoing dextral strain, we identify the structural settings most conducive to hydrothermal upwelling; these include fault tips, restraining bends, and fault intersections. We suggest that stress concentration in these settings results in higher fracture permeability, encouraging hydrothermal upwelling. On a broader scale (i.e., the entire Canadian Cordillera), thermal springs are correlated with regions with active seismicity, which highlights the importance of active strain in maintaining crustal permeability. There is interest in the development of geothermal energy resources in the Canadian Cordillera and the identification of these favourable structural and neotectonic settings may aid in the discovery of previously unidentified “blind” geothermal systems.