Basil Tikoff, Ph.D.
Professor of Structural Geology
Department of Geoscience
University of Wisconsin-Madison
The North American Cordillera experienced major contractional deformation during the Cretaceous-Paleogene, which is commonly attributed to normal subduction transitioning to shallow-slab subduction. This model is not consistent with new data from seismic tomography, detrital zircons, or transpressional deformation in the magmatic arcs: Flat-slab subduction has never been consistent with paleomagnetic data that indicates up to 3000 km of northward motion of the Insular Superterrane of Washington State, British Columbia, and Alaska. This talk explores the alternative hit-and-run model, in which the Insular Superterrane obliquely collided with the North American margin from 100-85 Ma (the “hit”), followed by northward translation during continued oblique convergence with North America from 85-55 Ma (the “run”). A critical element of this model is that Cordilleran orogenies were built on the rifted and irregular Precambrian margin the western North American margin, inherited from Rodinia breakup. The oblique collision of the Insular Superterrane along the jagged western edge of North America requires a three-dimensional, time-dependent view of the deformation along an irregular and evolving continental margin.