Noble Gases and Isotope Systematics in Continental and Hotspot Volcanism

9628481克雷格稀有气体系统学研究表明，大气气体通过注入最初溶解于海水的气体进入火山的岩浆室，从而污染原始岩浆中的深部地幔气体。一个主要的问题是，这一过程是局部的、区域性的还是全球性的，大陆和海洋热点火山是否都受到了类似的影响。PI建议通过对火山熔岩中橄榄石晶体中提取的惰性气体进行质谱分析来研究这一问题。与成因放射性同位素的对比将提供有关海洋和大陆火山环境中这一过程的性质和程度的信息。其次，3He为地幔热点提供了独特的特征，并可用于阐明大陆地区(如埃塞俄比亚热点)的热点轨迹。圆周率指数表明，氦的信号表明黄石公园火山中心是地幔热点，类似于埃塞俄比亚热点和海洋热点。通过测量沿这条轨迹熔岩中橄榄石晶体中的3He/3He比率，黄石公园的热点地区沿着蛇河平原向西南方向追溯到爱达荷州边界。建议继续进行这项研究，收集和分析从西缘到大陆边缘的橄榄玄武岩，以确定黄石热区最初是否在其远西缘与北美大陆相交。

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.