TONALITIC MAGMATISM, EXHUMATION, AND ROTATION ALONG THE BAKER-OLDS FERRY TERRANE BOUNDARY, BLUE MOUNTAINS, EASTERN OREGON
CA-ID-TIMS U-Pb zircon dating of pluton emplacement reveals a younging trend from SW to NE: Tureman Ranch (129.36 ± 0.06 Ma), Amelia (125.50 ± 0.08 Ma), Pedro Mountain (124.84 ± 0.07 Ma), and Lookout Mountain (123.84 ± 0.04 Ma). Geochemical analyses indicate that the plutons were sourced from mantle-derived and crustal melts of the juvenile accreted arc terranes. Hornblende geobarometry data are consistent with relatively shallow (< 3 kbar) emplacement depths. Ongoing thermochronological studies (40Ar/39Ar on hornblende and biotite and (U-Th)/He on zircon) will provide timing constraints on the exhumation of these plutons relative to similarly aged plutons associated with the Salmon River suture zone. Preliminary paleomagnetic results from two of these plutons indicate that the Blue Mountain terranes may have undergone significant vertical axis rotation since ~120 Ma. Overall, the age of plutonism in eastern Oregon is coeval with high-grade metamorphism and plutonism in the Salmon River suture zone, although the subsequent history appears to differ from adjacent cratonic North America.