HR: 0830h
AN: V31E-0979    [PDF]
TI: Basaltic Volcanism of the Bruneau-Jarbidge Eruptive Center and its Surroundings, Southwest Idaho: Chemical Evidence for Multiple Mantle Sources.
AU: * Vetter, S
EM: svetter@centenary.edu
AF: Dept. of Geology Centenary College, 2911 Centenary Blvd., Shreveport, LA 71104 United States
AU: Hanan, B
EM: barry.hanan@geology.sdsu.edu
AF: San Diego State University, Dept. Geological Sciences, San Diego, CA 92182 United States
AU: Shervais, J
EM: shervais@cc.usu.edu
AF: Utah State University, Dept. of Geology, Logan, UT 84322 United States
AB: The Bruneau-Jarbidge eruptive center is a large (95x55 km) structural basin at the southwest end of the eastern Snake River Plain, formed by the coalescence of several large, nested rhyolite calderas in response to passage of the Yellowstone hot spot circa 12.5 Ma. Within the eruptive center, basaltic lavas generally postdate the youngest rhyolites, which formed 8 Ma. NW-trending faults with small displacements that parallel the western Snake River Plain are common. Twenty-four volcanic vents are found within the eruptive center, along with numerous vents that lie outside the structural basin. Most vents are small shield volcanoes ($<=$ 5 km across) which rise a few hundred feet above the basin floor. Vents within the eruptive center are located along three distinct northwest trends; vents outside the eruptive center are more scattered but define at least one trend parallel to those inside the center. Sixty-eight samples were analyzed using XRF, microprobe, and ICP-MS. Basalts consist of plagioclase and olivine phenocrysts set in a groundmass of plagioclase, clinopyroxene, opaques, and glass. Basalts from within the Bruneau-Jarbidge eruptive center have Mg\# (100* Mg/[Mg+Fe] ranging from 38.5 to 61.3, with TiO2 = 1.2 to 2.4 wt%; FeO = 10.1 to 14.0 wt%, and P2O5 = .06 to .42 wt%. Trace element abundance's are: Nb = 6-16 ppm, Sr = 153-356 ppm, Zr = 67-261 ppm, LaN (chondrite normalized) = 22-65, and (La/Lu)N = 2 to 3.5. Basalts from outside the eruptive center have Mg\# = 38-42, TiO2 = 3.2-4.2 wt.%, FeO = 13.9-16.7 wt.%, P2O5 = 0.14-0.88 wt.%, Nb = 25-38 ppm, Sr = 267-373 ppm, Zr = 302-396 ppm, LaN = 125, and (La/Lu)N = 6.7x chondrite. These data show that the basalt samples from outside of the eruptive center are distinct from those erupted within the eruptive center; the differences in REE slopes indicate that these samples have distinct source regions and are not related by low pressure or high pressure fractionation. Overall, the range in compositions for basalts within the eruptive center samples are consistent with basalts of the eastern Snake River Plain. Basalts which erupted outside the BJ eruptive center are higher in Ti, Fe, and have much higher (La/Lu)N ratios, similar to basalts from the Western Snake River Plain. These sample may represent the southern extend of the WSRP as it migrates towards the southeast. The high TiO2-FeO may indicate a deeper source region than the eruptive center basalts, consistent with the high La/Lu ratios, which indicates residual garnet in the source.
DE: 1065 Trace elements (3670)
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting