TECTONICS OF THE COAST MOUNTAINS-CASCADES OROGEN: THE LEGACY OF BROWN, MONGER, AND WOODSWORTH

The Coast Mountains-North Cascades orogen records terrane accretion, metamorphism, and deformation, and contains the largest continental magmatic arc in the North American Cordillera. Fundamental contributions to our understanding of this orogen over the last 50 years have been made by Ned Brown, Jim Monger, and Glenn Woodsworth. In the 1960s, Monger in his Ph.D. (UBC) research recognized that major Cretaceous thrusting in the Cascades continued northward into British Columbia. He subsequently emphasized the importance of Tethyan fauna for large-scale transport in the Cordillera. This research in part led to his landmark 1982 synthesis (with colleagues) of superterranes and the origin of the Coast Mountains and Omineca belt, and then to his analysis with colleagues of Cordilleran suspect terranes. His mapping in the southern Coast Mountains in the 1980s and 1990s better established links between metamorphic and non-metamorphic units, and correlations across the Fraser-Straight Creek fault. Brown and his students at WWU wrote a series of papers in the 1970s and 1980s on high P/T metamorphism in the NW Cascades and San Juan Islands, and he was perhaps the first to place these rocks into a plate tectonic context. He also recognized the importance of major, nearly isothermal loading of the Cascades crystalline core. Brown further emphasized the tectonic implications of subhorizontal stretching lineations in the Cascades core, and later was the first to systematically explore detrital zircon age patterns in pre-Cenozoic units of the San Juans and North Cascades. Woodsworth’s pioneering mapping in the Coast Mountains began with his Ph.D. research at Princeton in the 1970s. His decades of careful mapping of the most challenging parts of the orogen provided a framework for subsequent research and numerous discoveries that have changed how we view the range. For example, he was part of early paleomagnetic studies that found shallow inclinations in Coast Mountain plutons, helping launch the paradigm-challenging Baja BC hypothesis. He also recognized that the Central Gneiss Complex was much younger than assumed, and so helped frame decades of study on exhumation processes in the orogen. Finally, an important part of the legacy of these individuals is their widespread collaborations and mentoring and support of students.