Factors controlling high elevations in the Canadian Cordillera: Isostatic analysis and thermal contributions

The Canadian Cordillera is characterized by higher mean elevation and thinner crust compared to the adjacent craton to the east, in apparent contradiction with the Airy isostatic model. Roy Hyndman hypothesized that the high Cordillera elevations may be supported by an overall hot, low-density Cordilleran backarc mantle, but this idea hasn't been tested at the regional scale. We use a new high-resolution crustal thickness model for western Canada derived from teleseismic receiver functions and active source data, to conduct a detailed analysis of elevation-crustal thickness trends in four distinct regions: forearc, backarc, foreland, and craton. The backarc and foreland regions have higher elevations relative to the forearc and craton, requiring additional buoyancy beneath these areas. Using a grid search, we find that unrealistically low crustal densities are required to explain the high elevations and, therefore, the support must come from below the crust. To isolate the mantle component, we use a global crustal density model to correct for the effects of crustal density variations. After correction, the elevation-crustal thickness trends in each area align with the Airy hypothesis. For a given crustal thickness, the elevation of the backarc region is ~700 m higher than that of the craton. This is consistent with uplift caused by a hot backarc mantle. However, the difference is lower than that determined for the entire North American Cordillera (~1600 m). This may suggest the mantle under the Canadian Cordillera is slightly cooler than regions to the adjacent US Cordillera, perhaps due to the absence of ongoing subduction.