Global mountain belts are commonly concluded to be a consequence of crustal thickening resulting from continental collision, with high elevations supported by crustal roots. However, accumulating seismic structure data indicate that many mountain belts have no crustal root. Most of the North American Cordillera has a 30–35 km crust, in contrast to 40–45 km for the lower elevation craton and other stable areas. It has been shown previously that most such mountain belts are in present or recent backarcs that are uniformly hot. From thermal constraints, we predict a uniform ∼1600 m elevation support of the Cordillera by thermal expansion compared to stable areas. Over most of the Cordillera, relative to stable areas, the elevations after correction for variable crustal thickness and density are in excellent agreement. When subduction and shallow backarc convection stop, the lithosphere may cool and the elevations of mountain belts subside over ∼300 m.y.

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