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

合作研究：确定核心是否可以成为终极高 3He/4He 源的计划

• 批准号: 2053366
• 负责人: Colin Jackson
• 金额: $ 43.88万
• 依托单位: Tulane University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2053366&HistoricalAwards=false
• 关键词: Collaborative; Research; plan; determine; core

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 project is jointly funded by EAR Petrology and Geochemistry and the Established Program to Stimulate Competitive Research (EPSCoR).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.

对稀有气体，如氦（He）的研究表明，地幔的一部分基本上没有在地球表面或地球表面附近融化。这些地幔域的特征是同位素3He与4He的高比值（3He/4He）。为了了解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作用下逃脱融化的，人们做了很多工作。对这些高3He/4He域的新观测表明，这些域可能是地核泄漏到地幔中的结果，而不是反映了以前未融化的地幔部分。通过这种泄漏，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率。随后，地幔岩石被运送到地表，并通过板内火山作用进行采样。该项目将包括在与地核温度和压力相似的条件下使用金属和岩浆进行实验，以探索地核是否是部分地幔中发现的高3He/4He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3He/4He的地幔结构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。这一提议旨在测试核心可能是最终高3He/4He源的假设。实验将在受控条件下进行，使金属和岩浆发生反应，其压力和温度可直接适用于地球内部的地核形成。利用激光烧蚀质谱法分析实验中稀有气体的分布。这些分析将得出有关核心在其形成过程中吸收惰性气体的能力的限制。这些约束将用于开发一个岩心地层模型，该模型可以在各种可能的地层条件下预测岩心中He和Xe的同位素组成。重要的模型参数包括岩心形成时间、地球原始大气的性质、与岩心形成相关的主要氧化还原状态以及岩心形成的压力-温度条件。模型预测将与现有的地球化学分析进行比较，以确定地核是否是高3He/4He惰性气体的合理来源。该提案将支持培训两名博士研究生，学习尖端的实验和分析方法，制作和表征稀有气体分析标准，这些标准将提供给社区，并为新奥尔良及其周边地区的大学生提供暑期实习。该项目由EAR岩石与地球化学和促进竞争性研究的既定计划（EPSCoR）共同资助。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。