The new generation of thermal ionization mass spectrometer to be purchased via funding from this grant will allow scientists at the University of Maryland to measure certain isotopic ratios to better than +5 ppm, a substantial improvement relative to measurements with our current equipment that are limited to approximately +25 ppm. The improved measurement capability will allow us to pursue a host of new Earth science projects that require ultra-high precision analysis. Specific analytical tasks to be tackled include the ultra-high precision analysis of 186Os/188Os ratios of mantle-derived rocks from putative plume sources, such as Hawaii, the Canary Islands and the Azores. Our previous work has suggested that enrichments in 186Os in some putative plume sources may reflect prior incorporation of outer core materials. We will continue to pursue this concept utilizing the superior measurement capabilities of the new instrument. We will also use the new instrument to test this hypothesis via examination of isotopes of tungsten. Cosmochemical observations coupled with mass balance arguments imply that Earth's core is depleted in 182W compared to the silicate portion of the Earth. Very slight depletions in this isotope in plume derived magmas would potentially implicate incorporation of core material. The predicted effects are so small that only the highest precision measurements, made possible with the new instrument, provide sufficient resolution necessary for this project. Unequivocal identification of a core component in a plume-derived rock could potentially settle major questions in geodynamics. ***
