New Insights on Mantle Volatiles from Noble Gas Radionuclides

“该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。“智力优势。稀有气体对地球上挥发物的起源以及大气和地幔的演化提供了至关重要的限制。然而，大气污染的幔源挥发物，一般复杂的解释。这项建议涉及的起源与地幔He签名，无论是裂谷带和俯冲有关的火山使用惰性气体放射性核素与其他化学和同位素数据。这些放射性核素在大气中的丰度极低（81 Kr ~10^-1/2，t1/2= 229000 yr; 85 Kr ~10^-11，t1/2= 10.8 yr; 39 Ar ~10^-15，t1/2= 269 yr），当与它们的来源分离时，它们就像计时器一样。这项提议的主要目的是利用这些放射性核素来解决“原始”挥发性样品中的表层空气污染，以及可能通过俯冲再循环到地幔的大气成分。这项工作将侧重于两个地点（格兰德河裂谷和波阿斯火山，哥斯达黎加），这两个地点的特点很好，很容易取样。分析需要使用以前用于研究富含CO2的地热气体的方法从大量散装气体（5，000升STP）中提取和纯化Kr和Ar。氪的纯化将在伊利诺伊大学芝加哥分校（UIC）进行，惰性气体放射性核素将在阿贡国家实验室通过原子阱痕量分析（ATTA; 81氪和85氪）进行分析，并在伯尔尼大学通过低水平计数（39 Ar）进行分析。样本的其他数据将在UIC、伯克利同位素地球化学中心和新墨西哥州大学（UNM）获得。建议的测量可能会提供决定性的限制，可以帮助解决一些长期存在的问题，对地球挥发物的起源，大气和海洋的演变，地表-地幔挥发物交换，地幔异质性，以及俯冲过程中挥发性元素的行为的影响。首席PI是一名早期职业女性调查员。来自UIC和UNM的几名本科生将参与采样仪器的开发和测试以及现场工作。该项目将扩大这些大学学习科目的多样性，并为不同群体的学生提供更广阔的视野和独特的机会。该项目还将加强哥斯达黎加和瑞士地球科学家之间的国际合作。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit. Noble gases provide crucial constraints on the origin of volatiles on Earth, and the evolution of the atmosphere and mantle. However, atmospheric contamination of mantle-derived volatiles, generally complicates interpretation. This proposal addresses the origin of the atmospheric component associated with the mantle He signature, both for a rift zone and a subduction-related volcano using noble gas radionuclides in conjunction with other chemical and isotopic data. These radionuclides are present in the atmosphere at extremely low abundance (81Kr~10^-12, t1/2=229000yr; 85Kr~10^-11, t1/2=10.8yr; 39Ar~10^-15, t1/2=269yr) and they act as chronometers when isolated from their source. The main objective of this proposal is to use these radionuclides to resolve superficial air contamination in 'primordial' volatile samples, as well as atmospheric components that may be recycled to the mantle via subduction. This work will focus on two localities (Rio Grande Rift and Poas Volcano, Costa Rica) that are well characterized and readily accessible for sampling. The analyses require the extraction and purification of Kr and Ar from large quantities of bulk gas (5,000 liter STP) using methods previously applied to study of CO2-rich geothermal gases. Purification of Kr will be performed at University of Illinois at Chicago (UIC), and noble gas radionuclides will be analyzed via Atom Trap Trace Analysis (ATTA; 81Kr and 85Kr) at Argonne National Laboratory and by low-level counting (39Ar) at University of Bern. Additional data for the samples will be obtained at UIC, Berkeley's Center for Isotope Geochemistry, and the University of New Mexico (UNM). The proposed measurements may provide decisive constraints that could help to resolve a number of long-standing questions regarding implications for the origin of terrestrial volatiles, evolution of the atmosphere and ocean, surface-mantle volatile exchange, mantle heterogeneity, and the behavior of volatile elements during subduction.Broader Impacts. The lead PI is an early career female investigator. Several undergraduate students from UIC and UNM will participate in development and testing of sampling apparatus as well as field work. This project will broaden the diversity of subjects studied at these universities, and provide broader views and unique opportunities to diverse populations of students. This project will also enhance international collaboration between geoscientists from Costa Rica and Switzerland.