Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.v11b2268j&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #V11B-2268
Physics
[1025] Geochemistry / Composition Of The Mantle, [1038] Geochemistry / Mantle Processes, [1040] Geochemistry / Radiogenic Isotope Geochemistry, [8137] Tectonophysics / Hotspots, Large Igneous Provinces, And Flood Basalt Volcanism
Scientific paper
The Snake River Plain (SRP) volcanic province is an 800 km track of basalt extending from the Owyhee Plateau to its current terminus, the Yellowstone Plateau. It is one of several late-Tertiary magmatic terranes that also include the Cascades magmatic arc, the Columbia River basalts, and the Oregon Plateau basalts; all of which are adjacent to the Basin and Range Province extensional system (Hughes and McCurry, 2002). This province represents the track of the Yellowstone plume and consists of basalt that is compositionally similar to ocean-island basalt. This basalt overlies a series of rhyolitic eruptive centers (overlapping caldera complexes, ignimbrites, and caldera-filling eruptions) that signal the arrival of the plume head (Christiansen, 2001) and herald the onset of plume-related rhyolitic and basaltic volcanism (Pierce et al., 2002). Observed within the SRP are two basalt types: the dominant low-K olivine tholeiites and less common high-K alkaline basalts. We report new Sr-, Nd-, and Pb-isotopic analyses of these two basalt types from all three SRP provinces: eastern, central, and western. Low-K tholeiites are enriched in 143Nd/144Nd and 86Sr/87Sr and forms a quasi-linear array in Pb-isotope space, along with Craters of the Moon and eastern SRP basalts. High-K lavas are found largely in the western plain, and have a uniquely different isotopic signature. They are depleted in 143Nd/144Nd and 86Sr/87Sr, relative to the low-K tholeiites, and plot closer to the BSE component of Zindler and Hart (1986). They also share the same Pb-isotopic space with high-K basalts from Smith Prairie (Boise River Group 2 of Vetter and Shervais, 1992). One low-K tholeiite - Eureka North, plots with these high alkali basalts. Mass balance models have demonstrated an increasing plume component from the Yellowstone caldera in the east to the craton edge in the west. The lavas analyzed in this study conform remarkably to this model. The mass fraction of plume component in western plain high-K lavas ranges to > 99%, higher than low-K thoileiites (97-99%) from the same region. This trend is controlled by ancient cratonic lithosphere like that of the Wyoming province. This province superimposes its inherent isotopic composition on sublithospheric plume and/or asthenospheric melts. Seismic tomography and upper mantle velocity variations coupled with these results demonstrate that the sub-continental lithospheric mantle was thermally eroded and removed after this area passed over the Yellowstone plume (e.g. Humphreys and co-workers). Removal of the SCLM apparently allowed upwelling and decompression melting of residual plume material occupying the eroded plume channel. This resulted in a mantle source where the plume:SCLM ratio was greater for high-K basalts, than the low-K tholeiite source. The change in mantle source regions could have happened in as little as 200,000 years (e.g., Vetter and Shervais, 2009).
Hanan Barry B.
Jean Marlon M.
Shervais John W.
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