Tracking the tectonic history of an ancient subduction zone, the North Cascades, Washington

The region within the North Cascades National Park represents the exhumed deep roots of a volcanic arc system that was active from 90 to 45 million years ago (Ma). The addition of magma to this area was unsteady during this time. Our research group has National Science Foundation funding to map, date, and collect geochemical data from the rocks within the park to determine when large additions of magma occurred. Our results indicate that there were major additions of magma from ~96–89 Ma, ~78–65 Ma, and ~50–45 Ma. Each pulse of magmatism introduced large amounts of heat into the crust, which can significantly weaken rocks and cause them to flow. This weakening is further enhanced if the arc’s lower crust is composed of sedimentary rocks that have been transferred to great depths through tectonic processes, which is the case for the North Cascades. Our current research aims to track how the emplacement of large volumes of magma into the crust ultimately affects crustal thickness and strength. Changes to these parameters will ultimately affect how the mountain range evolved through time.

Dr. Stacia Gordon
University of Nevada, Reno

Dr. Michael Eddy
Purdue University

Dr. Robert Miller
San Jose State University

Presentation given at North Coast & Cascades Science Days, 2024
go.nps.gov/sciencedays
[NOCA]