Structural geology of the Mount Meager Volcanic Complex, BC, Canada: implications for geothermal energy and geohazards

Abstract

The Mount Meager Volcanic Complex ( Qwe̓ lqwe̓ lústen or Mt. Meager) coincides tectonically with the intra-arc to back-arc transition zone and exhibits the loci of strain partitioning in response to a rapid change in orientation of the Pemberton and Garibaldi Arc segments that are coeval with a shift in Pacific plate motion after 5 Ma. This strain partition is manifested through development of a transpressional deformation from 5 to 1.9 Ma at the latitude of Mt. Meager. Mt. Meager is an active volcanic system with at least two explosive eruptions in the last 25 000 years, the most recent occurring around 2360 BP. Additionally, it is the site of the largest landslide in Canadian history, which occurred during the summer of 2010, originating from the southeastern side the massif. During early exploration at Mt. Meager, geothermal boreholes drilled to 3 km reached 270 °C but did not find sufficient permeability to sustain self-flowing conditions. To understand the geological challenges in Mt. Meager’s geothermal exploration, we analyzed outcrop-scale faults and folds, incorporating structural mapping, volcanic rock paleomagnetism, and radiometric dating to establish kinematic history and kinematic compatibility of structural geology features, including faults and folds. Our findings suggest that stress partitioning during the last 5 Ma resulted in the formation of a transpressional structure exhibited as an elongate and rhomboidal structure at Mt. Meager with anomalously high topographic elevations which led to east northeast–west southwest crustal shortening and exhumation of crystalline basement. This new structural geology model improves our understanding of the geothermal reservoir and potentially significant geohazards.