9628481 Craig Noble gas systematics show that atmospheric gases are introduced into magma chambers of volcanoes by injection of gases originally dissolved in ocean water, and thus contaminate the deep mantle gases in the pristine magma. A major question is whether this process is localized, regional, or global in extent, and whether both continental and oceanic hotspot volcanoes are affected in similar ways. The PI proposes to investigate this problem by mass spectrometric analyses of noble gases extracted from olivine crystals in volcanic lavas. Correlations with radiogenic isotopes will provide information as to the nature and extent of this process in the oceanic and continental volcanic environments. Secondly, 3He provides a unique signature for mantle hotspots, and can be used to elucidate hotspot tracks across continental regions (e.g., the Ethiopian hotspot). The PI has shown that the helium signature identifies the Yellowstone Park volcanic center as a mantle hotspot, akin to the Ethiopian hotspot and the oceanic hotspots. The Yellowstone hotspot has been tracked back along the Snake River Plain south-south-west to the Idaho border by measuring 3He/3He ratios in olivine crystals in lavas along this track. It is proposed to continue this study by collecting and analyzing olivine basalts from the western edge to the continental border, to determine if the Yellowstone hotspot originally intersected the North American continent at its far western edge.
