Defining the noble gas composition of highly depleted mantle domains

稀有气体在认识地幔结构和定量地幔的质量和挥发性通量方面起着重要作用。地幔中非放射性稀有气体的同位素组成可以限制我们星球上挥发性物质的来源以及挥发性物质被纳入固体地球的机制。此外，地幔中稀有气体的同位素组成可以为大气的起源和演化提供重要线索。例如，现代大气传统上被认为是次生的，即地球可能在吸积过程中获得的初级大气耗散后的地幔脱气。通过地幔脱气形成早期大气的理论现在正受到新的稀有气体数据和氖同位素的挑战。这项研究将使用稀有气体质谱法的新发展，它允许比以前更高的分辨率和精度测量，以检查一系列重稀有气体及其同位素比率，以确定最枯竭的地幔域的组成，并了解它们与正常和富集的中洋脊玄武岩来源的关系。问题包括：(1)贫、正、富地幔域稀有气体元素丰度比值；(2)不同地幔域氩、氙同位素异常是与古地幔分异事件有关，还是与板块俯冲再循环将大气稀有气体引入地幔有关；(3)贫、正、富地幔域中铀源和裂变生成的Xe的比例；(4)能否确定与地幔脱气有关的时间常数；(5) Xe和Kr的非放射性成因同位素组成是太阳的、球粒质的还是类似空气的，将予以讨论。这些问题的答案将使我们能够确定地幔中地幔柱向洋中脊玄武岩（MORB）源的挥发物和物质的通量，以及MORB和地幔柱源之间的混合程度。它还将提供有关地球结构和地幔流动的关键见解。此外，该研究还试图限制地球挥发物的来源和地壳、大气和地幔之间惰性气体的再循环，以及地球大气层的形成。这项工作的更广泛影响包括新的分析方法的开发，这将增加科学基础设施，使用美国国家科学基金会资助的质谱设备，以及学生的支持，包括支持在科学领域性别代表性不足的学生。其他影响包括将研究成果纳入研究生和本科课程。

The noble gases play an important role in understanding mantle structure and in quantifying mass and volatile fluxes in and out of the mantle. The isotopic composition of non-radiogenic noble gases in the Earth's mantle can constrain the sources of volatile sources on our planet and the mechanisms through which volatiles are incorporated into the solid Earth. Furthermore, the isotopic composition of the noble gases in Earth's mantle can provide important clues to the origin and evolution of the atmosphere. For example, the modern atmosphere was traditionally thought to be secondary, i.e, derived from mantle degassing after the dissipation of a primary atmosphere that the Earth might have acquired during the accretion process. Theories on the origin of the early atmosphere through degassing of the mantle are now being challenged by new noble gas data and neon isotopes. This research will use new developments in noble gas mass spectrometry that allow much higher resolution and precision measurements than previously available to examine a suite of heavy noble gases and their isotopic ratios to determine the composition of the most depleted mantle domains and understand how they relate to normal and enriched Mid Ocean Ridge Basalt sources. Issues such as: (1) the noble gas elemental abundance ratios in depleted, normal and enriched mantle domains, (2) whether isotopic anomalies in argon and xenon in different mantle domains are related to ancient mantle differentiation events or to the on going process of plate subduction and recirculation that introduces atmospheric noble gases into the mantle; (3) the proportion of Pu- to U-derived, fission generated Xe in depleted, normal, and enriched mantle domains; (4) whether there time-constants associated with mantle degassing can be determined; and (5) whether the non-radiogenic isotopic compositions of Xe and Kr are solar, chondritic, or air-like, will be addressed. Answers to these questions will allow determination of the flux of volatiles and material from plumes in the mantle into the mid-ocean ridge basalt (MORB) source and the degree of mixing between MORB and plume sources. It will also provide key insights on Earth structure and mantle flow. In addition, the research seeks to constrain sources of Earth volatiles and the recycling of noble gases between the crust and atmosphere and the mantle, and the formation of Earth's atmosphere. Broader impacts of the work include new analytical method development that will increase the infrastructure for science, use of a an NSF-funded mass spectrometry facility, and student support, including support of a student whose gender is under-represented in the sciences. Additional impacts include incorporation of research results into graduate and undergraduate courses.