Angela Stetson Master's Candidate

Angela Stetson Master’s Candidate

Titled "Orphan Basalts: Investigating the Petrogenesis of Unassigned Eastern Oregon Basalts," my thesis project is focused on detailing the origins of basalts mapped within the Telephone Butte, Calamity Butte and Craft Point quadrangles located along the boundary between the Harney Basin and the southern foothills of the Blue Mountains Province. Named for the localities in which basalt samples were collected, several basalt units are mapped in each quadrangle. Similarities in geochemical analyses of each basalt unit suggest that although these basalts have different unit names, they are in fact related and likely originated from the same source. 

For this thesis research, I have been working on classifying the origins of basalt and basaltic andesites mapped throughout eastern Oregon over the past seven years. I spent the last two summers geologically mapping the Craft Point 7.5-minute quadrangle in Harney County, Oregon, which has extensive basalt and basaltic andesite coverage. My main question was: “Where did these basalts come from?” Surrounding maps provided little clues to the source of these lavas. While some map reports suggested a Columbia River Basalt group origin, such as the Picture Gorge Basalt or Steens Basalt, others suggested the Strawberry Volcanics from the southern flanks of the Blue Mountains or even a previously undocumented volcanic event. Thus, I set out to determine the origins of the “orphan basalts,” hypothesizing that their source was 1) the Picture Gorge Basalt, 2) Steens Basalt, and/or 3) the basalt of the Strawberry Volcanics. 

Last summer, I collected more basalt samples as I continued my mapping project, including one sample from the unmapped House Butte quadrangle directly east of Craft Point. To add to the samples collected from Craft Point, samples collected from previous maps were added to this study, and their geochemical compositions were evaluated. Reported basalt and basaltic andesites from all nine regional geologic maps were compiled to build a dataset of 47 samples for classification. Two samples are still undergoing absolute age analysis; ten were made into polished thin sections. I am currently in the data processing stage of my research and have begun to make preliminary classification by correlating my samples to the geochemistry of previously published data for the Picture Gorge Basalt, Steens Basalt, and basalt of the Strawberry Volcanics.