22 Evolution of Cordilleran-type orogenic systems (Posters)

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Thermochronology at the southern edge of Siletzia records mid Eocene heating

Paper number: 22-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

New low-temperature thermochronology from 15 samples (AFT n=15, ZFT n=4) analyzed on rocks from near the suture zone between Siletzia and the Klamath Mountains terrane provide new constraints on regional thermal histories. Samples are from across the Wildlife Safari Fault in SW Oregon and include Dothan Formation meta-sedimentary rocks and Umpqua Group clastic sedimentary rocks. Together these samples represent deposition during the time before Siletzia accreted onto North America (Dothan Fm) and deposition of the Umpqua Group roughly syntectonic with Siletzia accretion circa 50 Ma.  AFT data from all these units appear to form a single age population around 45 Ma, requiring thermal resetting shortly after the time of deposition. AFT mean track lengths range from 12.52 μm to 14.14 μm indicating a similar degree of partial annealing across all samples. 

Initial ZFT analyses are limited to Dothan Formation meta-sedimentary basement samples to the southeast of the Wildlife Safari fault. These data seem to form a single Late Cretaceous age population circa 84 Ma, likely representing pre-depositional magmatic cooling of source zircons. Further AFT and ZFT work to expand analyses stratigraphically upward into the Umpqua Group and Tyee Formation NW of the Wildlife Safari fault is ongoing. 

AFT data are consanguineous despite significant tectonostratigraphic and structural diversity within the sample suite. We interpret this result as indicative of a thermal pulse that heated the rocks of our study area to at least AFT annealing temperatures in mid Eocene time, shortly after deposition of the overlying Tyee Formation. We hypothesize that this heating is reflective of a regionally pervasive thermal transient that is genetically linked with putative passing of the Yellowstone Hotspot under western Oregon, eruption of the Tillamook volcanics farther north in Siletzia, and thermal resetting of AFT data from Tyee Formation from a previous study. The timing and regional extent of thermal resetting documented here provides independent constraints on models of the early Yellowstone hotspot track, contributing new thermochronologic evidence to debates summarized by Wells et al. (2014). 

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410818

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