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，使得直接采样地球上最丰富的物质是不可能的。然而，样本已经到达地球？在各种火山岩或板块构造活动的表面。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工具应用于这些岩石，以便更好地限制地幔岩石的起源和地壳物质再循环回地幔的程度。最终，地幔和地壳/大气之间的挥发性化合物的转移是造成地球长期气候变化的原因。此外，高温热液蚀变的海洋岩石圈材料，其中包括浅地幔，已被证明是一个潜在的重要的储存库，为封存大气中的二氧化碳。在这项研究中提出的三重同位素的工作将更好地约束岩石圈的自然条件的变化，因为它包含挥发物，包括二氧化碳和水。除了这些科学影响之外，该项目还将资助一名第一代研究生和几名本科生。已经有几十项研究使用两种常见的氧同位素18-O和16-O的传统比例来限制地幔样品的起源和形成温度。由于只有一种同位素比（18-O/16-O）被测量，因此分析往往是模糊的。通过将第三种稀有的17-O同位素添加到混合物中，可获得的信息量明显更大。初步工作表明，平衡或不平衡的显着的情况下，将无法确定与18-O/16-O数据单独。最后，可以预见，地幔物质的三重同位素研究将成为广泛的幔源岩石研究的重要组成部分。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广大社区。这项工作将确定边界条件，如“原始地幔”和未改变的洋中脊玄武岩的三重同位素组成，改变的洋壳的三重同位素值的范围，并为更广泛的地质界提供标准，这一奖项反映了国家科学基金会的法定使命，并被认为值得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来支持。

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.