Triple Oxygen Isotope Investigation of Mantle Materials

按重量计算，地幔占地球的67%，但覆盖着5-10公里的洋壳或30-50公里的陆壳，这使得直接采样地球上最丰富的物质是不可能的。然而，样品已经到达地球？S表面的各种火山岩或受板块构造活动影响。本研究的目的是将三重氧同位素地球化学这一新的地球化学手段应用于这些岩石，以便更好地约束地幔岩石的起源和地壳物质回流到地幔的程度。归根结底，造成地球长期气候变化的是地幔和地壳/大气之间挥发性化合物的转移。此外，包括浅地幔在内的海洋岩石圈物质的高温热液蚀变已被证明是一个潜在的大气二氧化碳封存的重要储存库。这项研究中提出的三重同位素工作将更好地限制岩石圈变化的自然条件，因为它包含了包括二氧化碳和水在内的挥发物。除了这些科学影响，这个项目还将支持一名第一代研究生和几名本科生。已经有数十项研究使用氧的两种常见同位素18-O和16-O的传统比率来限制地幔样品的来源和形成温度。由于只有一种被测量的同位素比率(18-O/16-O)，分析往往含糊不清。通过在混合物中加入第三种稀有的17-O同位素，可获得的信息量明显更大。初步工作显示了不能仅用18-O/16-O数据确定的显著的平衡或不平衡实例。最后，可以预见，地幔物质中的三重同位素研究将是广泛研究地幔岩石的重要组成部分。因此，有必要为今后的工作奠定基础，以便使这一概念易于处理并适用于一般社区。这项工作将确定边界条件，如“原始地幔”和未改变的大洋中脊玄武岩的三重同位素组成，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。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.