Recycling of Noble Gases in Ring-bearing Silicates

含环硅酸盐中稀有气体的回收

• 批准号: 1347772
• 负责人: Stephen Parman
• 金额: $ 30万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-15 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347772&HistoricalAwards=false
• 关键词: Recycling; Noble; Gases; Ring; bearing

Volatiles such as water (H2O) and carbon dioxide (CO2) are well-known to be key to the climate and atmosphere of the Earth, and the life that depends on them. Less well known is that these volatiles are also abundant in the Earth's interior. Indeed, there is probably as much water inside the Earth as on the surface. Thus the transfer of volatiles in and out of the Earth exerts a fundamental control on both the climate and the large-scale movement of the Earth's interior. However, it is difficult to geochemically trace the major volatiles (H2O, CO2, S, Cl and F) as they have few isotopes, which are key geochemical tracing tools. The noble gases (He, Ne, Ar, Kr and Xe) are also volatile. Though low in concentration, they are isotopically rich and so are ideal for tracing the movement of volatiles. However, there is little data on how the noble gases behave at high pressures inside the Earth, greatly restricting their use as tracers. Building on our previous high-pressure noble gas experiments, this study will measure the solubility of noble gases in a range of minerals. This will allow better estimates of volatile fluxes into and out of the Earth, as well as better tracing of the geochemical evolution of the Earth's interior.The fundamental issue that will be addressed by the project is how noble gases are incorporated into subducting lithosphere (slabs). Subduction is the main mechanism for bringing volatiles into the mantle. Most models have assumed that noble gases, having no charge, would not bind into minerals, and so slabs would not contain significant noble gas contents. In a previous study, my group demonstrated that He, Ne and Ar are incorporated into amphibole and that they are bound into Si-O ring structures in the crystal lattice. Such ring structures are present in a variety of minerals in subducting slabs. The proposed research will use high-pressure experiments combined with laser-ablation noble gas mass-spectrometry to determine noble gas solubilities in ring-structured minerals (e.g. serpentine, chlorite and mica). The data will be used to quantify both the amount of noble gases incorporated into slabs as well as how the noble gases are fractionated from each other. The data will be used to construct models aimed at matching the observed noble gas concentration and isotopic ratios in the mantle, which will constrain rates of cycling of noble gases into the mantle. As the noble gases should trace the movements of H2O and CO2, the noble gas flux model will constrain H2O and CO2 cycling as well. This work fits well with a number of recent geochemical observations that indicate recycling of noble gases is more important than previously thought. It will provide the first measurements of noble gas solubilities in a range of minerals and so will allow, for the first time, quantitative estimates of noble gas recycling rates.

众所周知，水（H2O）和二氧化碳（CO2）之类的挥发物是地球气候和大气的关键，以及依赖它们的生命。 鲜为人知的是，这些挥发物在地球的内部也很丰富。 实际上，地球内部可能有大量的水与表面上一样多。 因此，挥发物进出地球的转移对地球内部的气候和大规模运动都产生了基本控制。 但是，很难在地球化学上追踪主要挥发物（H2O，CO2，S，CL和F），因为它们的同位素很少，这是关键的地球化学跟踪工具。 高贵的气体（HE，NE，AR，KR和XE）也是挥发性的。 尽管浓度较低，但它们在同位素上富含，因此是追踪挥发物运动的理想选择。 但是，关于贵族气体在地球内部高压力的行为如何极大地限制了它们作为示踪剂的使用，几乎没有数据。 在我们以前的高压高压气体实验的基础上，这项研究将测量各种矿物质中贵重气体的溶解度。 这将允许更好地估计挥发性通量进入地球，并更好地追踪地球内部的地球化学演变。 俯冲是将挥发物带入地幔的主要机制。 大多数模型都认为，没有电荷的贵重气体不会结合到矿物质中，因此平板不会包含明显的贵重气体含量。 在先前的研究中，我的小组证明了他，NE和AR被掺入闪石中，并且它们被结合到晶格中的Si-O环结构中。 这种环结构存在于俯冲板中的多种矿物质中。 拟议的研究将使用高压实验与激光燃气气体质量光谱法相结合，以确定环结构矿物（例如蛇纹石，氯酸盐和米奇）中的贵重气体溶解度。 数据将用于量化均匀纳入板的贵重气体以及如何相互分级的贵重气体。 数据将用于构建旨在匹配地幔中观察到的贵重气体浓度和同位素比的模型，这将限制贵重气体循环速率。 由于贵重气体应追踪H2O和CO2的运动，因此贵重气通量模型也将限制H2O和CO2循环。 这项工作非常符合许多最近的地球化学观察结果，表明贵重气体的回收比以前想象的更为重要。 它将在一系列矿物质中提供首次测量贵气体溶解度，因此首次允许对贵重气体回收率进行定量估计。