First Advisor

Martin J. Streck

Term of Graduation

Summer 2023

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Geology






dike swarm, Geochemistry, Geochronology, Large Igneous Provience, Petrology, Volcanology



Physical Description

1 online resource (xi, 105 pages)


The Columbia River Basalt Group is the youngest continental flood basalt province in the world and covers an aerial extent of 210,000 km2 covering Oregon, southern Washington, and eastern Idaho. Eruptions occurred between approximately 17 million and 6 million years ago, with 92% of eruptions occurring within the first million-year interval. Aside from mapping and some bulk compositional data, few studies have focused on the Chief Joseph dike swarm in NE Oregon, the main eruptive center of the Columbia River Basalt Group. Prior to this study there were no published age dates for the Chief Joseph dike swarm.

This project includes geochemical and petrographic data of 147 dikes across the main portion of Chief Joseph from the Oregon/Washington state border in the north to the southern extent of the swarm. This project also reports 40Ar/39Ar dates of 22 dikes from the northern and southern part of the study area. Developing a geochronological framework for magma activity at depth is significant in our understanding of storage and transport as well as for age relationship of intrusive CRBG magmas with ages and stratigraphy of subaerial lava flows vs. This project focuses on using geochemistry, petrography, and age dates to correlate select dikes of the Chief Joseph dike swarm with the units of the Grand Ronde Basalt, the Imnaha Basalt and other main phase formations, and on using that data to establish an age progression. Our new ages for subterraneous magmas of main phase units of the CRBG extend the age range of these formations and establishes ages for a newly identified Eckler-PGB type magma which is represented across the swarm. The new age of 17.22 ± 0.22 Ma for an Eckler-PGB like dike in the southern portion of the swarm establishes that the Chief Joseph dike swarm was active beginning at the same time as the Monument dike swarm began its activity further to the west. This suggests that the first eruptions of the CJDS began with magmas derived from a metasomatized shallow mantle with a strong subduction zone signature, which is reflected in the Eckler-PGB basalt followed by magmas that had a more plume like signature.

We conclude that there are age progressive trends in the geochemical signature of magmas becoming more evolved and younger along strike to the north. This study also supports the magma storage model put forth by Wolff et al. (2008) and Webb et al. (2019) where the main magma storage location is located in the Vale region of central eastern Oregon. This is supported by the geochemical diversity found in the southern portion which lies in the Vale region, there is a wider and older age range of dikes established in this area, and lastly the lack of silicic volcanism in the central or northern portion of the CJDS suggest little to no storage time of magmas sourcing the dikes there. This suggests that magma traveled from the southern portion of the CJDS in the Vale region to other eruptive locations throughout the swarm.


©2023 Mary Joyce Mass

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Available for download on Thursday, September 26, 2024

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