Lithospheric buckling of the Laramide foreland during Late Cretaceous and Paleogene, western United States

Abstract

Foreland deformation, in the form of arches or uplifts, occurred throughout the eastern Rocky Mountains region during the Laramide orogeny (75–50 Ma). Arches with the same structural style developed in the mid-continent region, east of the Rocky Mountains, although these were subsequently buried by Tertiary sedimentary rocks. We attribute deformation in the Rocky Mountain foreland and continental interior to folding of the entire lithosphere (lithospheric buckling) as a result of horizontal endload on the western edge of North America. The observed wavelength of arches in the western United States is ca. 190 km, a spacing consistent with a lithospheric buckling interpretation. This buckling model provides a mechanical explanation for the distinction between “thin-skinned” Sevier-style and “thick-skinned” Laramide-style deformation, which depends respectively upon the decoupling or coupling of lithospheric layers. Additionally, the buckling model explains concurrent tectonism east of the Rocky Mountains during Late Cretaceous time. Dextral shearing within the block uplifts indicates that the deformation was broadly transpressional during the Laramide orogeny.