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Orogenic Examples |
Department of Geological Sciences, University of Idaho, Moscow, ID 83844-3022, USA wmcclell{at}uidaho.edu
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.
