The effects of crustal thickening and extensional collapse of continental crust, combined with variations in plate-convergence forces, provide a coherent explanation for evolution of the Cretaceous-early Tertiary Sevier-Laramide orogeny. Crustal thickening of the Sevier-Laramide hinterland region was triggered by the combination of compressive plate-convergence forces and subduction-induced conductive heating of the crust. Eastward progradation of the locus of Sevier-Laramide deformation through time reflects the progressive widening of the region of crustal thickening. The region of maximum crustal thickening migrated outward until about 80 to 75 Ma, when it encountered excessively strong lithosphere of the Colorado Plateau. The locus of deformation was then transmitted laterally across both a hinterland that had attained maximum crustal thickness and the rigid Colorado Plateau, into the Laramide Rocky Mountain foreland. An episode of vigorous extensional collapse of orogenically thickened crust affected the southern Cordillera between about 75 and 35 Ma. Early Tertiary waning of plate-convergence rates and continued subduction-induced conductive heating of thickened crust allowed extensional collapse along the southern Cordillera region to drive the Colorado Plateau block northward. The result was the late Laramide phase of Rocky Mountain foreland deformation. Because of this, compressive deformation in the central and southern Laramide Rocky Mountain region continued through Eocene time, rather than ceasing at 56 Ma, as it did in the northern Cordillera.

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