Collaborative Research: A plan to determine if the core can be the ultimate high 3He/4He source

对氦（He）等稀有气体的研究表明，地幔的部分区域在很大程度上避免了地球表面或附近的熔化。这些地幔域的特征是同位素3 He/4 He比值很高。 人们已经做了很多工作来了解这些地球内部的地幔域是如何在数十亿年的地幔对流和板块构造面前逃脱融化的。对这些高3 He/4 He域的新观察表明，这些域可能是地核泄漏到地幔中的结果，而不是反映以前未熔化的地幔部分。通过这种泄漏，来自地核的原始惰性气体将它们的氦比率印在位于地核-地幔边界之上的地幔岩石上。随后，地幔岩被搬运到地表，并通过板内火山作用取样。该项目将涉及在与地核相似的温度和压力下使用金属和岩浆进行实验，以探索地核是否是地幔部分中发现的高3 He/4 He的来源。如果这是真的，并且地核是来源，这将提供关于地核化学的新信息，并意味着高3 He/4 He地幔域实际上可能不是未熔化的和原始的。这有助于我们了解地球的早期演化。 这一提议旨在检验核心可能是终极高3 He/4 He源的假设。 将进行实验，使金属和岩浆在受控条件下发生反应，这些条件的压力和温度可直接适用于地球内部的核心形成。实验中的惰性气体分布将使用激光烧蚀质谱法进行分析。 这些分析将产生关于堆芯在其形成过程中吸收惰性气体的能力的限制。这些限制将被应用于开发一个核心的形成模型，预测的同位素组成的核心，他和氦的各种合理的形成条件。 重要的模型参数包括核心形成的时间，地球的原始大气的性质，与核心形成相关的普遍氧化还原状态，以及核心形成的压力-温度条件。模型预测将与现有的地球化学分析进行比较，以确定核心是否是高3 He/4 He惰性气体的合理来源。 该提案将支持对两名博士生进行尖端实验和分析方法方面的培训，并支持制作和表征将向社区提供的惰性气体分析标准，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响进行评估来支持审查标准。

Studies of noble gases, such as helium (He), suggest that parts of the mantle have largely escaped melting at, or near, the Earth’s surface. These mantle domains are characterized by high ratios of the isotopes 3He to 4He (3He/4He). Much work has been done to understand how these mantle domains within Earth’s interior have escaped melting in the face of billions of years of mantle convection and plate tectonics. New observations of these high 3He/4He domains suggest that, rather than reflecting previously unmelted portions of the mantle, these domains may be the result of Earth’s core leaking into the mantle. Through this leak, pristine noble gases from the core imprint their helium ratios on mantle rocks that sit above the core-mantle boundary. Subsequently, the mantle rocks are transported to the surface and sampled by intraplate volcanism. This project will involve experiments using metal and magma at temperatures and pressures similar to the Earth’s core to explore the question of whether the core is the source of the high 3He/4He found in parts of the mantle. If true, and the core is the source, this would provide new information about the chemistry of the core and would mean that high 3He/4He mantle domains may not, in fact, be unmelted and pristine. This helps us understand Earth’s early evolution. This proposal seeks to test the hypothesis that the core can be the ultimate high 3He/4He source. Experiments will be conducted that react metal and magma under controlled conditions that range up to the pressures and temperatures directly applicable to core formation within Earth. The noble gas distribution in the experiments will be analyzed using laser-ablation mass spectrometry. These analyses will yield constraints regarding the ability of the core to incorporate noble gases during its creation. These constraints will be applied towards developing a core formation model that predicts the isotopic composition of the core for both He and Xe for various plausible formation conditions. Important model parameters include core formation timing, nature of Earth’s primordial atmosphere, the prevailing redox state associated with core formation, and core formation pressure-temperature conditions. Model predictions will be compared to existing geochemical analyses to identify if the core is a plausible source of high 3He/4He noble gases. This proposal will support the training of two PhD students in cutting-edge experimental and analytical methods, the production and characterization of noble gas analytical standards that will be made available to the community, and summer internships for college students in and around New Orleans.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.