Defining the noble gas composition of highly depleted mantle domains

稀有气体在了解地幔结构、量化进出地幔的质量通量和挥发分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源的来源，以及挥发物并入固体地球的机制。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要的，即来自于地球在吸积过程中可能获得的初级大气消散后的地幔脱气。早期大气通过地幔脱气而形成的理论现在正受到新的惰性气体数据和霓虹灯同位素的挑战。这项研究将利用惰性气体质谱学的新发展，使测量分辨率和精确度大大提高，以检查一套重惰性气体及其同位素比率，以确定最贫乏的地幔区域的组成，并了解它们与正常和浓缩的中洋脊玄武岩来源之间的关系。这些问题包括：(1)贫化、正常和富集区的稀有气体元素丰度比；(2)不同地幔域内的Ar、Xe同位素异常是否与古代地幔分异事件有关，或与正在进行的板块俯冲和再环流将大气稀有气体引入地幔的过程有关；(3)在贫化、正常和富集区产生裂变产生Xe的比例；(4)是否存在与地幔脱气有关的时间常数；以及(5)Xe和Kr的非放射性同位素组成是否为太阳、球粒陨石或空气。对这些问题的回答将有助于确定从地幔中的羽流进入大洋中脊玄武岩(MORB)源的挥发物和物质的通量，以及MORB和羽流源之间的混合程度。它还将提供关于地球结构和地幔流动的关键见解。此外，这项研究还试图限制地球挥发性物质的来源、稀有气体在地壳、大气和地幔之间的循环，以及地球大气的形成。这项工作的更广泛影响包括将增加科学基础设施的新分析方法的开发，使用NSF资助的质谱学设施，以及学生支持，包括支持在科学中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.