Cordilleran crustal structure of southern British Colombia and northeastern Washington: A new regional cross section linking foreland deformation to the orogenic interior

A new crustal-scale cross section is constructed across the Cordillera in southwestern Canada and the northwestern United States utilizing deep seismic reflection data. This section provides new perspectives on the relationships between deformation in the foreland and the orogenic interior that include the following: (1) Stratigraphic correlations and geometries within the upper crust preclude major offsets on Tertiary extensional faults. (2) The base of contractional deformation deepens from ∼5 km in the east to the base of the crust ∼30 km in the orogenic interior. (3) The presence of Precambrian rocks in the core complexes, and small offsets on bounding normal faults, results in arc assemblages that are less than ∼5 km thick along the section. These results are consistent with interpretations that late Mesozoic to early Tertiary contraction and foreshortening of the entire crust occurred west of the Purcell Anticlinorium, propagating eastward to the thrust and fold belt.