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。该项目调查地球表面和地幔之间通过俯冲和火山作用的氮循环。研究和公共服务将在伍兹霍尔海洋研究所进行。俯冲带在全球地球化学循环中起着至关重要的作用，特别是对于挥发性元素，如氢，碳，硫，氯和氮（N），它们主要通过火山脱气返回地表。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部的程度以及控制深层氮封存的因素仍然未知。在这个项目中，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区（SVZ）数十座火山的氮输出，2）确定弧岩浆中的氮来源。这项工作涉及确定氮浓度和同位素比在小包裹体的流体被困在晶体之前，氮已脱气地球表面。在WHOI任职期间，PI将与马萨诸塞州布罗克顿的新高地特许学校（6-12年级）合作，开发与俯冲和火山作用相关的教材和演示，这些教材和演示可以直接纳入马萨诸塞州的物理科学国家标准。他还将通过WHOI的REU项目指导暑期本科生。通过俯冲带和火山弧进行的挥发物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的星球。然而，对深N周期的全球视角才刚刚开始出现。地幔是否是一个净源（通过火山作用）或净汇（通过俯冲）的N仍然是一个有争议的话题，可能在很大程度上取决于俯冲板片的热演化。研究人员将使用手头的样品产生两个全面的沿弧N和δ 15 N数据集，检查矿物中的流体包裹体分离自基性岩弧熔岩沿着CAVA和SVZ。因为这些系统是热相似的，但有不同的N源和俯冲动力学，这些数据允许通过俯冲带和火山弧的N循环的地质控制隔离。N2/3 He和N2/Ar的比值将限制氮通量沿着这些弧段，而δ 15 N将允许源判别。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N纯化线，避免了现代大气中的样品污染，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。