HR: 0800h
AN: V21B-0615    [Abstracts]
TI: Genesis of a Chemically Enriched Olivine Tholeiite from the Eastern Snake River Plain, Idaho
AU: * Chadwick, C G
EM: siliciclaire@yahoo.com
AF: Dept. of Geosciences, Idaho State University, Pocatello, ID 83209 United States
AU: Hughes, S S
EM: hughscot@isu.edu
AF: Dept. of Geosciences, Idaho State University, Pocatello, ID 83209 United States
AU: McCurry, M
EM: mccumich@isu.edu
AF: Dept. of Geosciences, Idaho State University, Pocatello, ID 83209 United States
AU: Chadwick, J
EM: chadjohn@isu.edu
AF: Dept. of Geosciences, Idaho State University, Pocatello, ID 83209 United States
AB: The eastern Snake River Plain (ESRP) volcanic province is overlain by 1-2 km of dominantly Quaternary olivine tholeiite lava flows associated with the Yellowstone hotspot. A second highly evolved geochemical basalt suite has been identified in previous studies, typified by the lava flows of Craters of the Moon National Monument (COM). Geochemical data from three new coreholes drilled on the ESRP was collected to correlate chemically distinct basaltic flow groups and to evaluate chemical changes in ESRP basaltic magmatism over time. The coreholes extend to a depth of approximately 800 ft and penetrate lava flows from 200,000 to 640,000 years old, allowing the temporal geochemical variability of the ESRP to be studied in this area. One flow group, known as the "high-K" flow, identified in two of these cores, is unusually enriched in incompatible major and trace elements relative to ESRP olivine tholeiites. Isotopic data for this flow group ($^{87}$Sr/ $^{86}$Sr = 0.70599 - 0.70604; $^{143}$Nd/ $^{144}$Nd = 0.512431 - 0.512446) suggest derivation from a slightly different, isotopically less enriched magma reservoir than most ESRP olivine tholeiites ($^{87}$Sr/ $^{86}$Sr = 0.70640 - 0.70765; $^{143}$Nd/ $^{144}$Nd = 0.512261 - 0.512474). Major and trace element data suggest that a combination of lower-degree partial melting and more extensive fractional crystallization contribute to the evolved chemistry of the high-K flow. The geochemistry of the high-K flow reflects differences in source chemistry and petrogenetic processes compared to both the ESRP olivine tholeiites and the highly evolved basalt suite (COM), and may represent an intermediate chemical suite of ESRP basalts.
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
DE: 1099 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting