Helium-Carbon Dioxide Relationships in Mid-Ocean Ridge Basalts and Upper Mantle Geodynamics

P.I.：Michael提案编号：98-11161 机构：University of Tulsa塔尔萨大学大洋中脊玄武岩和上地幔地球动力学中的氦-二氧化碳关系碳和水在地质时期通过洋壳和沉积物的俯冲而循环，可能大量地进入地幔深部。 相比之下，海洋岩石的氦同位素系统学支持地幔柱从地球深处相对不含原始挥发物的地区上升的假设。 因此，在火山活动中释放的主要挥发物，如二氧化碳和水，在多大程度上是年轻的，而不是被板块构造循环利用，这是地球化学中的一个基本问题。 氦的地球动力循环与碳的地球动力循环密切相关。 3 He/4 He比值沿着大洋中脊系统存在系统的地理变异，但其确切原因并不总是很清楚。 在某些情况下，它们可能与来自地幔深部的高3 He/4 He物质的局部上涌有关。 在其他情况下，它们可能是由于从U和Th的放射性衰变中加入的4 He的差异。 原则上，准确的二氧化碳/氦比变化的知识可以用来区分这些可能性，但这种方法的全面发展取决于更好地定义地幔CO2/He比的精细尺度变化。 本研究的目的是准确地确定3 He/4 He和CO2/He比值的上地幔在大西洋，太平洋和印度洋的洋中脊玄武岩的测量。

P.I.: MichaelProposal Number: 98-11161 Institution: University of TulsaTitle: Helium-carbon dioxide relationships in mid-ocean ridge basalts and upper mantle geodynamicsCarbon and water have been recycled over geologic time through subduction of oceanic crust plus sediments, possibly in significant quantities to the deep mantle. In contrast, helium isotope systematics of oceanic rocks support the hypothesis of mantle plumes rising from regions deep in the Earth which are relatively undegassed of their primordial volatile inventory. The extent to which major volatiles released during volcanism, such as carbon dioxide and water, are juvenile rather than recycled by plate tectonics is therefore a fundamental question in geochemistry. The geodynamic cycle of helium is closely linked to that of carbon. There are systematic geographic variations in 3He/4He ratio along the mid-ocean ridge system, but their exact cause is not always well understood. In some cases they may be tied to localized upwelling of high 3He/4He material from the deep mantle. In other cases they may be due to differences in the addition of 4He from the radioactive decay of U and Th. In principle, an accurate knowledge of variations in the carbon dioxide/helium ration cna be used to distinguish between these possibilities, but the full development of such an approach depends on a better definition of fine-scale variations in the mantle CO2/He ratio. The purpose of this study is to accurately determine the 3He/4He and CO2/He rations for upper mantle regions beneath the Atlantic, Pacific and Indian Ocean from measurements on mid-ocean ridge basalts.