Noble Gas Behavior During Upper Mantle Deformation

上地幔变形过程中稀有气体的行为 该提案寻求资金，以检验变形是地幔矿物中惰性气体含量的重要控制因素这一假设。这一假说是基于对圣保罗岩（赤道大西洋）和洋底高度剪切岩石（糜棱岩）的系统研究。初步研究表明，He含量随变形程度而变化，变形程度最大的超糜棱岩中He含量最高。耦合真空破碎和熔融实验表明，大部分的氦和氖的糜棱岩中包含的矿物基质，而不是流体或熔体包裹体：只有5至18%的总氦被释放的破碎。圣保罗岩石中的He/Ne比值随变形和矿物学而变化很大（~ 20倍），最高的He/Ne比值（和氦浓度）发现于最细粒度的超糜棱岩橄榄岩中。这表明，非常高的氖和氦含量的变形岩石中有关的缺陷在地幔压力的扩散捕获。然而，目前的数据集仅限于非常少量的样品，矿物学和蚀变的影响需要进行评估。建议在圣保罗岩进一步测量以检验气体变形假说，并探索矿物学对氦、氖和氩的同位素和元素丰度的影响。 圣保罗岩石样品中氦的浓度是如此之高，以至于提出了新的激光聚变实验来直接确定氦的驻留地点。此外，在两个蛇绿岩：约瑟芬（俄勒冈州，美国）和阿曼的几个剪切带的系统采样建议。这两个蛇绿岩中的剪切带是理想的，因为变形特征有很好的记录，并且现场暴露足以允许从未变形到变形的橄榄岩的完整断面采样。 岩石和矿物中稀有气体同位素的测量是地球科学界广泛关注的问题。地幔岩中稀有气体的研究对于地球深部模型的建立是非常重要的，因为在一些海洋岛屿中发现的非放射性稀有气体同位素组成提供了少数几个支持地球深部未脱气储层存在的观测结果。这项研究跨越了同位素地球化学和矿物物理学之间的传统学科界限，这可能会在我们对这两个领域的理解方面产生重要的进展。变形假说的验证需要重新评估地幔熔融期间惰性气体行为以及气体沿地壳中沿着迁移的模型。这将支持麻省理工学院/WHOI海洋学联合项目的研究生和博士后研究员。关于圣保罗岩石的工作还将涉及与两名巴西地球科学家的合作（S。Sichel和T.坎波斯），并将促进来自巴西和WHOI的学生和科学家之间的国际交流。

Noble Gas Behavior During Upper Mantle DeformationIntellectual merit.  This proposal seeks funds to test the hypothesis that deformation is an important control on noble gas contents in mantle minerals. This hypothesis is based on a systematic study highly sheared rocks (mylonites) from St. Paul's Rocks (equatorial Atlantic ocean) and from the ocean floor. Preliminary study shows that He content varies with degree of deformation, with the highest contents in the most deformed ultramylonites. Coupled vacuum crushing and melting experiments show that most of the helium and neon within the mylonites is contained in the mineral matrices rather than fluid or melt inclusions: only 5 to 18% of the total helium is released by crushing. He/Ne ratios in St. Paul's Rocks vary widely (~ 20x) with deformation and mineralogy, with the highest He/Ne ratios (and helium concentration) found in the finest grained ultramylonite peridotite. It is suggested that very high neon and helium contents in deformed rocks is related to diffusive trapping within defects at mantle pressures. However, the present data set is limited to a very small number of samples, and the influences of mineralogy and alteration need to be assessed. It is proposed to test the gas-deformation hypothesis with further measurements at St. Paul's Rocks and to explore the influence of mineralogy on the isotopes and elemental abundances of helium, neon and argon. Helium concentrations are so high in the St. Paul's Rocks samples that new laser fusion experiments are proposed to directly determine the helium residence sites with in situ measurements. In addition, a systematic sampling across several shear zones at two ophiolites: Josephine (Oregon, USA) and Oman is proposed. The shear zones in these two ophiolites are ideal because deformation characteristics are well documented and field exposures are sufficient to allow sampling of complete transects, from undeformed to deformed peridotite.Broader impacts.  Noble gas isotope measurements in rocks and minerals are of broad interest to the earth science community. Studies of noble gases in mantle derived rocks are important to models of the earth's deep interior because unradiogenic noble gas isotopic compositions, found in some oceanic islands, provide some of the few observations that support the existence of deep undegassed reservoirs in the earth. This research crosses the traditional disciplinary boundaries between isotope geochemistry and mineral physics, which may yield important advances in our understanding of both fields. Validation of the deformation hypothesis would require reevaluation of models for noble gas behavior during mantle melting as well as gas migration along faults in the crust. This will support a graduate student in the MIT/WHOI Joint Program in Oceanography and a Postdoctoral Investigator. The work on St. Paul's Rocks will also involve collaboration with two Brazilian geoscientists (S. Sichel and T. Campos), and will foste international exchanges between students and scientists from Brazil and WHOI.