Defining the noble gas composition of highly depleted mantle domains

定义高度贫化地幔域的稀有气体成分

• 批准号: 1464484
• 负责人: Sujoy Mukhopadhyay
• 金额: $ 32.59万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-10-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1464484&HistoricalAwards=false
• 关键词: Defining; noble; gas; composition; highly

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.

稀有气体在了解地幔结构和定量地幔内外物质和挥发分通量方面起着重要作用。地球地幔中非放射性惰性气体的同位素组成可以限制我们星球上挥发性来源的来源以及挥发性物质融入固体地球的机制。此外，地幔中稀有气体的同位素组成可以为研究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级的，即在地球可能在吸积过程中获得的原始大气消散后，来自地幔脱气。关于早期大气层起源于地幔脱气的理论现在正受到新的惰性气体数据和氖同位素的挑战。这项研究将使用惰性气体质谱法的新发展，这种质谱法允许比以前更高的分辨率和精确度测量，以检查一套重惰性气体及其同位素比率，以确定最贫化的地幔域的组成，并了解它们与正常和富集的大洋中脊玄武岩源的关系。问题如下：（1）亏损、正常和富集地幔域的稀有气体元素丰度比;（2）不同地幔域的氩、氙同位素异常是否与古地幔分异事件有关，还是与正在进行的板块俯冲和再循环过程将大气中的稀有气体引入地幔有关;（3）在亏损区、正常区和富集区中，Pu和U源的裂变生成钚的比例，（4）是否存在与地幔脱气有关的时间常数;（5）Kr和Kr的非放射成因同位素组成是太阳源的、南极源的还是类似于空气的。 这些问题的答案将允许确定的挥发物和物质的通量从地幔柱到洋中脊玄武岩（MORB）源和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稀有气体在地壳与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新的分析方法开发，这将增加科学基础设施，使用NSF资助的质谱设施，以及学生支持，包括支持性别在科学中代表性不足的学生。其他影响包括将研究成果纳入研究生和本科生课程。