Dr. Baasil Tikoff
UW Madison

Topic: The hit-and-run model for the Cretaceous-Paleogene North American Cordillera: The role of alternative hypotheses

Academic host: Craig Jones

Abstract: This talk has something for everyone: It proposes a new tectonic model for how the Rocky Mountains formed, why community-accepted models are so difficult to overcome, and a new way of communicating about the relation between data and model uncertainty.  The North American Cordillera experienced major contractional deformation during the Cretaceous-Paleogene, which is commonly attributed to normal subduction transitioning to shallow-slab subduction. I propose an 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”).  The hit phase records dextral transpressional deformation in all of the magmatic arcs, incipient plateau formation, foreland block uplifts in the northern Rocky Mountains, and significant foreland sedimentation in adjacent North America. The 85-55 Ma “run” phase resulted in dextral strike-slip faulting of coastal blocks and significant contractional deformation in adjacent North America. The presentation will address the utility of alternative models and the role of uncertainty in both data and models. The concept of salience allows one to connect data uncertainty to model uncertainty.  The hit-and-run model is consistent with the first-order geological and geophysical constraints from the Cordillera, although it requires a more complex (three-dimensional, time-dependent, etc.) view of mountain building along western North America.