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）等挥发物是地球气候和大气以及依赖它们的生命的关键。 鲜为人知的是，这些挥发物在地球内部也很丰富。 事实上，地球内部的水可能与地球表面的水一样多。 因此，挥发物进出地球的转移对气候和地球内部的大规模运动都有根本的控制作用。 然而，主要挥发物（H2O，CO2，S，Cl和F）的同位素很少，难以进行地球化学示踪，而这些同位素是关键的地球化学示踪工具。 稀有气体（He、Ne、Ar、Kr和Xe）也是挥发性的。 虽然浓度低，但它们富含同位素，因此是追踪挥发物运动的理想选择。 然而，关于惰性气体在地球内部高压下的行为的数据很少，这极大地限制了它们作为示踪剂的使用。 在我们以前的高压惰性气体实验的基础上，这项研究将测量惰性气体在一系列矿物中的溶解度。 这将有助于更好地估计进出地球的挥发性通量，并更好地追踪地球内部的地球化学演变，该项目将处理的根本问题是惰性气体如何融入俯冲岩石圈（板块）。 俯冲作用是挥发分进入地幔的主要机制。 大多数模型都假设惰性气体不带电荷，不会与矿物结合，因此板不会含有大量的惰性气体。 在以前的研究中，我的团队证明了He，Ne和Ar被纳入角闪石中，并且它们被束缚在晶格中的Si-O环结构中。 这种环形结构存在于俯冲板块中的各种矿物中。 拟议的研究将使用高压实验结合激光烧蚀惰性气体质谱法，以确定惰性气体在环状结构矿物（如蛇纹石、蛇纹石和云母）中的溶解度。 这些数据将用于量化板中惰性气体的含量以及惰性气体如何相互分离。 这些数据将用于构建模型，以匹配地幔中观测到的惰性气体浓度和同位素比率，这将限制惰性气体循环进入地幔的速度。 由于惰性气体应跟踪H2O和CO2的运动，因此惰性气体通量模型也将约束H2O和CO2循环。 这项工作与最近的一些地球化学观测结果非常吻合，这些观测结果表明惰性气体的再循环比以前认为的更重要。 它将首次测量惰性气体在一系列矿物中的溶解度，从而首次对惰性气体再循环率进行定量估计。