Crustal Thickness and Elevation of the North American Cordillera From the Late Cretaceous to the Early Miocene

Abstract Cordilleran‐type orogenic systems are characterized by high elevation regions that form in the hinterland of long‐lived convergent continental arcs. Despite their global tectonic and climatic significance, reconstructing past surface elevations and crustal thicknesses of these highlands has proved difficult, necessitating new methodological approaches. Here we apply geochemical proxies to expand the spatial and temporal resolution of paleoelevation and paleocrustal thickness estimates in the North American Cordillera (30–49°N). We compiled arc geochemical data ( n = 11,865) from the Late Cretaceous to the Early Miocene (95–17 Ma). Using new chemical “mohometers,” we construct maps of crustal thickness and elevation at 1 Ma intervals. We also generate time series for the southern, central, and northern segments of the orogen, calculate crustal thickness at the onset of metamorphic core complex exhumation, and compare our results to previous stable isotope paleoaltimetry studies. Results indicate that a Paleogene highland was continuous for 1,500 km along‐strike of the North American Cordillera, consistent with previous stable isotope, structural, and geochemical data. This region was characterized by crustal thicknesses between 50 and 60 km (mean = 54.8 km) and paleoelevations between 3 and 4 km (mean = 3.6 km). In the central and southern segments (Nevada and western Arizona) crust at least 50 km thick was present until the Early Miocene, which suggests that thickened crust was maintained for a protracted interval following Cretaceous shortening. These results indicate that most crustal thinning was contemporaneous with a change in plate boundary conditions along the western North American margin.