TIMING OF VOLCANISM IN CENTRAL OREGON: DATING THE TAM MCARTHUR RIM VOLCANO
In this study we present new geochronology, petrography, mineral chemistry, and whole rock geochemistry of lava flows from the rim. Flow compositions vary significantly, ranging from andesites to thick obsidian flows. Some flows are aphyric with trachytic flow textures while others are crystal rich lacking flow textures. We provide new 40Ar/39Ar geochronology which shows lower portions of the rim are ~185 ka, suggesting volcanism is younger than previously calculated K-Ar ages. The new age data suggest the Tam McArthur edifice was constructed relatively quickly, likely within a 10 ka period. Constraining the timing of past volcanism associated with the TVF provides insights into potential future hazards, allowing for awareness and implementation of informed mitigation strategies within Central Oregon communities.