Evolution of the North American Cordillera

Sedimentary logging in Wyoming – with Megan Mueller & Mara Page.

Eocene-Oligocene outcrops in the rainshadow of the Oregon Cascades

Improving our knowledge of the topographic evolution of the North American cordillera

The tight correlation between subduction, crustal deformation, climate and life is particularly well illustrated in the North American Cordillera, where successive continental accretions and changes in subduction dynamics along the Pacific subduction zone have resulted in the development of numerous mountain ranges and intra-plate basins. These successive orogenies had a dramatic impact on regional ecosystems, inducing an important rainshadow effect which led to aridification at the continental scale; a small amount of uplift in the Cascade Mountain Range (Pacific Northwest) was likely enough to anchor the Cordilleran Ice Sheet during recent glacial periods and significantly enhance global cooling. In turn, these climatic and environmental changes had a strong positive feedback on the mountain ranges themselves, leading to enhanced erosion and encouraging greater uplift. However, current paleogeographic and tectonic models for the build-up of the North American cordillera suffer from limited information about the timing of topographic build-up, particularly in the Pacific Northwest or in the American Southwest. The topographic evolution in these areas remain less understood than in California, Nevada, or Utah, and have not been integrated into a broader model for orogenic development.

This project aims to document the topographic evolution of several key mountain ranges in the North American cordillera to determine when was elevation attained relative to crustal deformation. It includes a vast program of stable isotopic measurements to establish paleoelevation estimates in a temporal context by means of improved depositional ages of synorogenic deposits by U-Pb geochronology, as well as reconstruction of past fluvial drainages. These data will provide a new basis for interpreting the paleotopographic evolution of North America, and how it might have impacted regional climate and biota.

Collaborators and (former) students: Samuel Shekut (University of British Columbia, Vancouver), Brenden Britt (University of Texas, Austin), Alex Lowe (University of Washington, Seattle), Ralph Haugerud (USGS).

Topical papers:

S. Shekut & A. Licht (2020). Late middle Miocene emersion of the Olympic Peninsula shown by sedimentary provenance. Lithosphere (1): 7040598.

R. Leary, P. Umhoefer, M. Smith, T. Smith, J. Saylor, N. Riggs, G. Burr, E. Lodes, D. Foley, A. Licht, M. Mueller & C. Baird (2020). Provenance of Pennsylvanian-Permian sedimentary rocks associated with the Ancestral Rocky Mountains orogeny in southwestern Laurentia: implications for continental-scale Laurentian sediment transport systems. Lithosphere 12,  88-121.

A. Licht, J. Quade, A. Kowler, M. De Los Santos, A. Hudson, A. Schauer, K. Huntington, P. Copeland, T. Lawton (2017). Impact of the North American monsoon on isotope paleoaltimeters: implications for the paleoaltimetry of the American Southwest. American Journal of Science 317, 1-33.