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

对惰性气体，如氦(He)的研究表明，地幔的一部分在很大程度上没有在地球表面或附近融化。这些地幔区域具有高的3He/4He同位素比值(3He/4He)。人们已经做了很多工作来了解地球内部的这些地幔区域是如何在数十亿年的地幔对流和板块构造的情况下逃脱融化的。对这些高3He/4He区域的新观察表明，这些区域可能是地核泄漏到地幔中的结果，而不是反映先前未融化的地幔部分。通过这次泄漏，来自地核的原始惰性气体在地核-地幔边界上方的地幔岩石上留下了它们的氦比例。随后，地幔岩石被输送到地表，并被板内火山作用采样。该项目将利用金属和岩浆在与地核相似的温度和压力下进行实验，以探索地核是否是在地幔部分发现的高3He/4He的来源的问题。如果是真的，并且地核是源，这将提供关于地核化学的新信息，并将意味着高3He/4He地幔区域实际上可能不是未熔化和原始的。这有助于我们了解地球的早期演化。这一提议试图验证核心可能是最终的高3He/4He源的假设。将进行实验，使金属和岩浆在受控条件下反应，最高可达直接适用于地球内部核心形成的压力和温度。实验中的惰性气体分布将用激光烧蚀质谱仪进行分析。这些分析将对地核在其形成过程中吸收惰性气体的能力产生限制。这些约束将被应用于开发一个岩心形成模型，该模型预测在各种可能的形成条件下He和Xe的岩心同位素组成。重要的模型参数包括核心形成时间、地球原始大气的性质、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，以确定核心是否可能是高3He/4He惰性气体的来源。这项提议将支持两名博士生在尖端实验和分析方法方面的培训，将向社区提供的惰性气体分析标准的生产和表征，以及新奥尔良及其周边地区的大学生暑期实习。该奖项反映了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。

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.