UNDERGRADUATE COHORT RESEARCH EXPERIENCE INVESTIGATING THERMO-TECTONIC RESPONSE OF THE NORTHERN KLAMATH MOUNTAINS TO EOCENE SILETZIA COLLISION

Early Eocene collision of the oceanic Siletz terrane with the western North American continental plate led to the modern Cascadia Subduction Zone. The suture zone between Siletzia and the northern Klamath Mountains (NKM) is well preserved, however, the response of the North American plate to collision is poorly constrained. This is due to the lack of the Cenozoic rock record in the NKM. We, a cohort of six undergraduate students and two faculty mentors, collected six bedrock samples from five Jurassic-Cretaceous plutons from the NKM along a NNW-SSE transect south of the suture zone. These plutons were targeted for both apatite and zircon (U-Th)/He thermochronometry, which can be used to reconstruct time-temperature histories and reveal the timing and rates of crustal exhumation.

New zircon (U-Th)/He dates (n=35; 7 samples) and apatite (U-Th)/He dates (n=15; 3 samples) will allow us to test several hypothesized thermal histories, including: (1) primarily Eocene dates may indicate rapid cooling at the time of Siletzia collision and suggest a major orogenic event that resulted in the crustal thickening, (2) a wide range of dates with no spatial pattern may indicate that the Siletzia collision was not a primary control on cooling, or (3) Neogene dates may suggest that post-collision tectonics overprinted earlier thermal histories.

This research project was used to pilot a novel cohort approach during the ‘22-’23 academic year that focused on making place-based, collaborative, and authentic research more accessible to undergraduate students. The six student members of the cohort will co-present this work, supported by an inaugural AGeS-DiG award.