Constraining nitrogen sources and recycling efficiency in hot subduction zones using fluid inclusions in mineral separates from mafic lavas

利用镁铁质熔岩矿物分离物中的流体包裹体限制热俯冲带的氮源和回收效率

• 批准号: 2324745
• 负责人: Michael Hudak
• 金额: $ 37.7万
• 依托单位: Williams College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-04-01 至 2024-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2324745&HistoricalAwards=false
• 关键词: Constraining; nitrogen; sources; recycling; efficiency

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).This project investigates nitrogen recycling between Earth’s surface and the mantle through subduction and volcanism. The research and public service will be conducted at the Woods Hole Oceanographic Institution (WHOI). Subduction zones play a critical role in global geochemical cycles, especially for volatile elements such as hydrogen, carbon, sulfur, chlorine, and nitrogen (N) that largely return to the surface through volcanic degassing. While nitrogen is the most abundant gas in Earth’s atmosphere, the extent to which it can return to the deep mantle through subduction and, the factors that control deep N sequestration, remain unknown. For this project, the researcher will 1) quantify nitrogen outputs from dozens of volcanoes in the Central America Volcanic Arc (CAVA) and the Southern Volcanic Zone (SVZ) of the Chilean Andes, and 2) identify the sources of N in arc magmas. This work involves determining N concentrations and isotope ratios in small inclusions of fluids that are trapped in crystals before N has been degassed to Earth’s surface. During his tenure at WHOI, the PI will partner with New Heights Charter School (Grades 6-12) in Brockton, MA to develop teaching materials and demonstrations related to subduction and volcanism that can be directly incorporated into the Massachusetts state standards for physical sciences. He will also mentor summer undergraduate students through the REU program at WHOI.Volatile recycling through subduction zones and volcanic arcs modifies Earth’s atmospheric composition and helps to maintain a stable climate and a habitable planet over geologic time. However, a global perspective on the deep N cycle is only beginning to emerge. Whether the mantle is a net source (via volcanism) or a net sink (via subduction) of N remains a subject of debate and may be largely governed by the thermal evolution of the subducting slab. The researcher will use samples that in hand to produce two comprehensive, along-arc N and δ15N data sets, examining fluid inclusions in mineral separates from mafic arc lavas along the CAVA and the SVZ. Because these systems are thermally similar but have distinct N sources and subduction dynamics, these data allow for the isolation of geologic controls on N recycling through subduction zones and volcanic arcs. Ratios of N2/3He and N2/Ar will constrain N fluxes along these arc segments while δ15N will allow for source discrimination. This project leverages the unique analytical capacity of a Nu Noblesse HR noble gas mass spectrometer connected to a dedicated sample crushing and N purification line at WHOI, avoiding sample contamination from the modern atmosphere, and providing the highest precision subduction zone N data currently available.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该奖项全部或部分由《2021 年美国救援计划法案》（公法 117-2）资助。该项目研究通过俯冲和火山作用在地球表面和地幔之间的氮循环。研究和公共服务将在以下地点进行。伍兹霍尔海洋研究所 (WHOI) 的俯冲带在全球地球化学循环中发挥着至关重要的作用，特别是对于氢、碳、硫、氯和氮 (N) 等挥发性元素。虽然氮是地球大气中最丰富的气体，但它通过俯冲作用返回地幔深处的程度以及控制深层氮封存的因素仍然未知。 ，研究人员将 1) 量化中美洲火山弧 (CAVA) 和智利安第斯山脉南部火山带 (SVZ) 数十座火山的氮排放量，以及 2) 确定弧内氮的来源这项工作涉及在 N 被脱气到地球表面之前确定晶体中的小包裹体中的 N 浓度和同位素比率，PI 将与 New Heights 特许学校（6-12 年级）合作。 ）在马萨诸塞州布罗克顿开发与俯冲和火山作用相关的教材和演示，这些材料和演示可以直接纳入马萨诸塞州物理科学标准。他还将通过 REU 项目指导暑期本科生。通过俯冲带和火山弧的挥发性循环改变了地球的大气成分，有助于在地质时期维持稳定的气候和宜居行星。然而，关于地幔是否存在的全球深氮循环的观点才刚刚开始出现。氮的净源（通过火山作用）或净汇（通过俯冲）仍然是一个争论的话题，并且可能在很大程度上受到俯冲板片的热演化的控制。研究人员将使用现有的样本来产生两个。全面的沿弧 N 和 δ15N 数据集，检查沿 CAVA 和 SVZ 的镁铁质弧熔岩中的矿物分离物中的流体包裹体，因为这些系统在热学上相似，但具有不同的 N 来源和俯冲动力学，因此这些数据允许分离通过俯冲带和火山弧对 N 循环进行地质控制，N2/3He 和 N2/Ar 的比率将限制沿这些弧段的 N 通量，而 δ15N 将允许进行来源区分。该项目利用了 Nu Noblesse HR 惰性气体质谱仪的独特分析能力，该质谱仪连接到 WHOI 的专用样品破碎和氮纯化生产线，避免了现代大气中的样品污染，并提供了目前可用的最高精度的俯冲带氮数据。该奖项通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。