Collaborative Research: RUI: An undergraduate cohort thermochronology research and mentorship experience investigating the thermo-tectonic record of the northern Klamath Mountains

Cal Poly Humboldt Sponsored Programs Foundation, Arcata CA

Investigators

Abstract

The geologic history of mountain building events is chronicled in the rock record, especially along former tectonic plate boundaries. Approximately 56 million years ago, a large basaltic oceanic plateau, the Siletzia-Crescent terrane, erupted off what is now the coast of the Pacific Northwest. A few million years after eruption, it collided with North America, and is proposed to have caused i) tectonic plate rotations, ii) mountain building and major regional-scale faulting, and iii) the subduction zone plate boundary to jump westward, establishing the modern Cascadia subduction zone. Today, the southern edge of Siletzia-Crescent terrane collision is preserved as a sliver of basaltic rock thrust on older sedimentary rocks in southern Oregon. Few syn-collisional sedimentary rocks survive from the time of Siletzia collision, rendering direct investigation of the effect of the collision challenging. To overcome this challenge, the investigators will target specific minerals in older, crystalline rocks from the northern Klamath Mountains, located south of the collision suture. Using this approach, the research team will reconstruct the burial, thickening, uplift, and erosion history of the region in response to collision. Geochemical analysis of these mineral chronometers is an application commonly used to address large scale tectonics questions, however, the advanced technique is typically available only to scientists at large, primarily research-oriented institutions. In this project, the principal investigators will center a group of undergraduate researchers at Cal Poly Humboldt and Oregon State University, locations that straddle the geologic region of interest, to reconstruct the tectonic history of the southern Siletzia-North American collisional zone, by applying multiple mineral chronometers, in a collaborative, academic-year, cohort-based undergraduate research experience. Siletzia formation and subsequent accretion marks a major shift in western U.S. subduction tectonics. The timing of Siletzia collision is coincident with the shut off of Farallon slab subduction and predates the formation of the modern Cascadia subduction zone and arc. The Siletzia terrane comprises the basement rock over a 600 km stretch of western North America from Roseburg, OR to Vancouver Island. However, the spatial and thermal impact of Siletzia accretion on the North American continent is not well understood, largely due to a missing and overprinted geologic and thermal record. The investigators will center undergraduate student research contributions through a novel, year-long, comprehensive cohort experience. The research team will apply multi-method mid- and low-temperature thermochronometry to northern Klamath Mountain samples to assess the continent’s response prior to, during, and following Siletzia accretion. Results will address a major knowledge gap in regional evolution of the Cascadia Subduction Zone, have implications for the thermal and spatial magnitude and rate of exhumation, burial, and deformation driven by accretion tectonics on overriding continental plates, address challenges resolving tectonic and landscape evolution events that are missing from the rock record using multi-method thermochronometry, and engage undergraduate students as primary research contributors guided by three Principal Investigators with overlapping expertise. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.