Xenoliths reveal a hot Moho and thin lithosphere at the Cordillera-craton boundary of western Canada

Abstract

Abstract Properties of the lithosphere control the transitions in elevation and plate deformation from hot, mobile orogenic belts to cooler, stronger cratons. The sharp, abrupt boundary of the North American Cordillera with the craton in western Canada has been suggested to be a result of recent (<50 Ma) heating and delamination of the lithosphere. To test this, we queried the fine structure in the thermal history of the mantle lithosphere approaching this transition using mantle xenolith thermobarometry. The xenoliths sampled by their host lava within ~20 km of the Cordillera-craton boundary require thinner lithosphere (by 20 km) and a hotter Moho (by 200 °C) compared to those sampled 180 km away. A hot, weak lithosphere at the boundary explains a topographic low that parallels this transition for a large length of the North American Cordillera, possibly from focused heat during edge convection. The cooling pattern of geothermometers applied to the xenoliths also suggests that any delamination event producing thinner lithosphere in the orogen is unlikely to have occurred in the past 50 m.y.