Date of Graduation

Summer 2024

Degree

Master of Natural and Applied Science in Geography, Geology, and Planning

Department

Geography, Geology, and Planning

Committee Chair

Matthew McKay

Abstract

The Salmon River suture zone in western Idaho records the Jurassic-Cretaceous (160-90 Ma) accretion of amalgamated volcanic arc terranes onto the North American continent. Rocks exposed at the surface record burial to depths of more than 20 kilometers, with unclear drivers for uplift and exhumation. Two competing hypotheses have been proposed to explain the transport of deep crustal rocks to the surface: (1) delamination of a dense lithospheric root resulted in rapid isostatic uplift of the crust and (2) exhumation of crustal blocks along thrust faults. To test these models, I present temperature-time (T-t) paths for mid-crustal metamorphic rocks constructed using U-Pb ages of zircon, apatite, and rutile, accompanied by closure temperature estimates for apatite and rutile presented in context with local structural relationships. Samples from higher-grade metamorphic rocks were found to have higher closure temperatures and older ages than juxtaposed lower grade rocks, suggesting initial exhumation in higher grade crustal blocks before juxtaposition and transport to the surface. These findings align with the hypothesis indicating that exhumation occurred as a series of thrust faults.

Keywords

zircon, apatite, rutile, closure temperature, metamorphic rocks, salmon river suture zone, U-Pb geochronology, thermochronometry, accreted terrane

Subject Categories

Geology | Geophysics and Seismology | Tectonics and Structure

Copyright

© Jonathan J. Cone

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