Triple Oxygen Isotope Investigation of Mantle Materials

地幔占地球重量的67%，但被5-10公里的海洋地壳或30-50公里的大陆地壳覆盖，这使得对地球上最丰富的物质进行直接采样是不可能的。然而，样本到达地球了吗？S表面的各种火山岩或受板块构造活动影响。将三氧同位素地球化学这一新的地球化学工具应用于这些岩石，是本研究的目的，以便更好地约束地幔岩石的起源和地壳物质回地幔的循环程度。最终，是地幔和地壳/大气之间挥发性化合物的转移导致了地球长期气候的变化。此外，包括浅层地幔在内的海洋岩石圈物质的高温热液蚀变已被证明是封存大气CO2的潜在重要储存库。本研究提出的三同位素工作将更好地约束岩石圈蚀变的自然条件，因为它包含了挥发物，包括CO2和水。除了这些科学影响外，该项目还将支持第一代研究生和几名本科生。已有数十项研究使用氧的两种常见同位素（18-O和16-O）的传统比例来限制地幔样本的起源和形成温度。由于只测量了一种同位素比率（18-O/16-O），因此分析结果往往模糊不清。通过添加第三种稀有的17-O同位素，可获得的信息量大大增加。初步的工作表明，仅用18-O/16-O数据无法确定平衡或不平衡的显著实例。最后，预计地幔物质的三同位素研究将成为幔源岩广泛研究的重要组成部分。因此，有必要为未来的工作提供基础，以便使该概念易于处理并适用于一般社区。这项工作将定义“原始地幔”和未蚀变中洋脊玄武岩的三重同位素组成等边界条件，以及蚀变洋壳的三重同位素值范围，并为更广泛的地质界提供标准。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The mantle composes 67% of Earth by weight, but is overlain by a 5-10 km oceanic crust or 30-50 km continental crust, making direct sampling of the most abundant material on the planet impossible. However, samples have reached the Earth?s surface in various volcanic rocks or by plate tectonic activity. It is the purpose of this study to apply the new geochemical tool of triple oxygen isotope geochemistry to these rocks in order to better constrain the origin of mantle rocks and the degree of recycling of crustal material back into the mantle. It is ultimately the transfer of volatile compounds between the mantle and crust/atmosphere that is responsible for changes in the long-term climate of the planet. Furthermore, high temperature hydrothermal alteration of oceanic lithospheric material, which includes the shallow mantle, has been shown to be a potentially important repository for sequestration of atmospheric CO2. The triple isotope work proposed in this study will better constrain the natural conditions of alteration of the lithosphere as it incorporates volatiles, including CO2 and water. In addition to these scientific impacts, this project will support a first-generation graduate student, and several undergraduate students.There have been dozens of studies that use the traditional ratio of the two common isotopes of oxygen, 18-O and 16-O, to place constraints on the origin and temperature of formation of mantle samples. Because there is only one isotope ratio being measured (18-O/16-O), the analyses are often ambiguous. By adding the third rare 17-O isotope to the mix, the amount of information available is significantly greater. Preliminary work shows remarkable instances of equilibrium or disequilibrium that would not be identified with the 18-O/16-O data alone. Ultimately, it is envisioned that the triple isotope research in mantle materials will be an important component of broad-based studies of mantle-derived rocks. As such, it is necessary to provide a foundation for future work, in order to make the concept tractable and applicable to the general community. This work will define the boundary conditions, such as the triple isotope composition of "pristine mantle" and unaltered mid-ocean ridge basalts, the range of triple isotope values of altered oceanic crust and provide standards to the broader geological community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.