Evolution of the Seven Devils Volcanic Arc and Period of Amalgamation with the North American Craton Based on Zircon U/Pb Geochronology and Hf Isotope Geochemistry of Intrusions in the Seven Devils Mountains, Western Idaho (USA)

The Seven Devils Mountains are located in the Wallowa-Whitman National Forest in western Idaho. These mountains expose a geologically complex and variably metamorphosed terrane which preserves the Permo-Triassic volcanic arc accreted against the Cordilleran margin. Due to its geologic complexity, the origins of the Seven Devils Mountains and therin correlations between it, the Wrangellia terrane, and Blue Mountains Province terranes are uncertain. Zircon U/Pb and Lu/Hf analyses were used to enhance the geologic history of this complex terrane and act as steppingstone for further work in testing proposed ties to the Wrangellia and Blue Mountains Province terranes. LA-ICP-MS zircon U/Pb dating on six samples of intermediate intrusive rocks yield ages ranging from 120.1 to 137 Ma with the average age of 127 Ma. All samples have similar Lu/Hf isotopic compositions, with a range in εHf(t) of 8.6 to 13.8 with the average εHf(t) value of 10.8. Isotopic and age data show that intrusive rocks were forming close to the time of accretion. These new data combined with previous age and isotope data shows more similarities between the Seven Devils volcanic arc and the Blue Mountains Province than the Wrangellia terrane, however more extensive research is needed to truly decipher the complex history of these amalgamated terranes.