The structural settings of convective hydrothermal systems in southeastern British Columbia, Canada

A concentration of thermal springs with outlet temperatures ranging from ~20-80 ̊C occurs in the southeastern corner of British Columbia, Canada, and is an attractive target for geothermal energy exploration. There is no active or young volcanism in the immediate vicinity (within 100s of km), and yet the crustal heat flow in this region is relatively high (~80-100 mW/m). Geothermometry of spring water suggests that reservoir temperatures range between ~40-180 ̊C, indicating that some circulation systems reach depths of 2-5 km based on past estimates of geothermal gradients. The thermal springs occur in association with several major fault zones, which may permit deep circulation of fluid through fractured reservoirs. In other fault-hosted geothermal systems (e.g., Great Basin, Rhine Graben), hydrothermal circulation has been shown to correspond to zones of enhanced permeability caused by localized extension, high fracture density, and/or active slip and dilation. Here, we present data from new structural mapping in the major fault zones of southeastern British Columbia. Our dataset of fault plane and slickenline orientations suggests a recent, possibly post-Eocene, phase of dextral strike-slip faulting not previously identified by regional mapping. The NNE-SSW stress field required for these kinematics is similar to the present-day stress field derived from crustal earthquake focal mechanisms. Future geothermal exploration efforts in this area should focus on fault segments oriented favourably for slip and dilation within this stress field.