Abstract Late Cretaceous–Early Tertiary contractional deformation along the Cordilleran margin of North America is represented by two distinct styles of foreland deformation, thin-skinned and thick-skinned, that primarily differ in depth to their respective basal décollements. Given the coeval nature of contraction in regions experiencing different styles of deformation, displacement on deep-level detachments associated with thick-skinned basement-cored uplifts in the southern Rocky Mountains was kinematically linked with displacement along shallow-level detachments in the southern Canadian Rockies. In the central North American Cordillera, the transition in foreland décollement depth was accommodated by a NW-trending oblique ramp system. The oblique ramp extended from the basement-cored uplifts of Wyoming along the northern margin of the Idaho batholith to the Shuswap crustal duplex in southeastern British Columbia. While accommodating transfer between differing structural levels, the Late Cretaceous to Paleocene displacement on the oblique ramp produced uplift and exhumation of high-grade metamorphic and plutonic rocks of the Idaho batholith between the NW-striking Lewis and Clark line and the Orofino shear zone. This resulted in truncation of the transpressional western Idaho shear zone, and may have localized the site of Eocene extension in this portion of the Cordillera.

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Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Abstract The early Mesozoic evolution of the U. S. Cordillera differs greatly from its previous history of mainly miogeoclinal sedimentation with outboard marginal-basin-island-arc mobile zones. The Early Mississippian and Permian-Triassic thrust emplacement of eugeoclinal strata across the miogeocline signaled the initial propagation of subduction-related tectonism onto the sialic edge. Following these events, the sialic edge and the resulting accreted terranes became an active continental margin. The active margin history records not only eastward subduction of oceanic crust beneath North America, but also the formation, migration, and accretion of marginal basin and fringing island-arc systems along the continental margin. At the close of the Jurassic, the fringing arc-marginal basin system collapsed, resulting in a more direct interaction of major Pacific basin plates with hte Cordilleran margin. Such interactions are manifested by Andean and San Andreas types of marginal regimes which characterized the Cretaceous and Cenozoic. In this chapter we will discuss the tectonic evolution of the U. S. Cordilleran margin during the early phases of its active margin history (Triassic through Jurassic).