Geochemistry and Thermobarometry for Granitic Rocks at the Intersection of the Sevier Orogeny and Priest River Core Complex near Tumtum, WA
Faculty Mentor
Dr. Chad Pritchard
Presentation Type
Poster
Start Date
May 2025
End Date
May 2025
Location
PUB NCR
Primary Discipline of Presentation
Geology
Abstract
Eastern Washington hosts an array of granitic intrusions ranging from about 96 to 48 million years old. EWU has collected about 20 U/Pb ages in Spokane, Lincoln, and Stevens Counties; this project focuses on samples from one outcrop outside of Tumtum, WA. The outcrop consists of two different granitic textures, one of which has been dated to 68.7 Ma +/- 0.9 (1.4). The dated sample is course-grained and best represents the outcrop as whole, while the other sample is an inclusion of finer-grained material with more mafic mineralization. Analysis of both samples included thin section observation, whole rock X-ray fluorescence (XRF) and inductively-coupled mass-spectrometry (ICP-MS), micro-XRF scans, SEM imaging and EDS analyses. A close look at feldspar minerals and biotite alteration using these methods provide thermobarometer indicators, allowing for creation of a graph for the Pressure-Temperature-Time (P-T-t) Path. Understanding the pressure and temperature conditions for crystallization and subsequent alterations contributes to the ongoing data collection that increases our understanding of the formation and timing of Washington and Idaho’s regional tectonics, specifically the Priest River Core Complex (PRC). Understanding how the PRC has developed and stressed the crust will allow us to better understand the mechanisms and structures that have a large impact on economic mineralization, groundwater flow through structures, and potentially continued seismic issues (like the Spokane Earthquake Swarm of 2001) in the Spokane region.
Recommended Citation
Smith, Marilyn L., "Geochemistry and Thermobarometry for Granitic Rocks at the Intersection of the Sevier Orogeny and Priest River Core Complex near Tumtum, WA" (2025). 2025 Symposium. 15.
https://dc.ewu.edu/srcw_2025/ps_2025/p1_2025/15
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Geochemistry and Thermobarometry for Granitic Rocks at the Intersection of the Sevier Orogeny and Priest River Core Complex near Tumtum, WA
PUB NCR
Eastern Washington hosts an array of granitic intrusions ranging from about 96 to 48 million years old. EWU has collected about 20 U/Pb ages in Spokane, Lincoln, and Stevens Counties; this project focuses on samples from one outcrop outside of Tumtum, WA. The outcrop consists of two different granitic textures, one of which has been dated to 68.7 Ma +/- 0.9 (1.4). The dated sample is course-grained and best represents the outcrop as whole, while the other sample is an inclusion of finer-grained material with more mafic mineralization. Analysis of both samples included thin section observation, whole rock X-ray fluorescence (XRF) and inductively-coupled mass-spectrometry (ICP-MS), micro-XRF scans, SEM imaging and EDS analyses. A close look at feldspar minerals and biotite alteration using these methods provide thermobarometer indicators, allowing for creation of a graph for the Pressure-Temperature-Time (P-T-t) Path. Understanding the pressure and temperature conditions for crystallization and subsequent alterations contributes to the ongoing data collection that increases our understanding of the formation and timing of Washington and Idaho’s regional tectonics, specifically the Priest River Core Complex (PRC). Understanding how the PRC has developed and stressed the crust will allow us to better understand the mechanisms and structures that have a large impact on economic mineralization, groundwater flow through structures, and potentially continued seismic issues (like the Spokane Earthquake Swarm of 2001) in the Spokane region.
