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.

该奖项是根据2021年《美国救援计划法》的全部或部分资助的（公共法117-2）。该项目通过俯冲和火山主义调查了地球表面与地幔之间的氮回收。该研究和公共服务将在伍兹霍尔海洋学机构（WHOI）进行。俯冲带在全球地球化学循环中起着至关重要的作用，尤其是对于诸如氢，碳，碳，硫，氯和氮（N）等挥发性元素，这些元素在很大程度上通过火山脱水返回了地面。虽然氮是地球大气中最丰富的气体，但通过俯冲可以通过俯冲返回到深陆地的程度以及控制深n隔离的因素仍然未知。对于该项目，研究人员将1）量化来自中美洲火山弧（CAVA）（CAVA）和智利安第斯山脉的南部火山区（SVZ）的数十个火山的氮输出，以及2）在弧岩中确定N的来源。这项工作涉及确定n浓度和同位素比在少量烟道中，这些烟道被困在晶体中，然后n脱水到地球表面。在WHOI任职期间，PI将与位于马萨诸塞州布罗克顿的New Heights Charter School（6至12年级）合作，开发与俯冲和火山主义有关的教学和示威活动，这些示范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计划进行心理夏季的本科生，通过俯冲带和火山弧的挥发性回收修改了地球的大气组成，并有助于在地质时间维持稳定的气候和可居住的星球。但是，对深n周期的全球视角才刚刚开始出现。地幔是净来源（通过火山源）还是n的净水槽（通过俯冲）仍然是争论的主题，并且可能在很大程度上受俯冲板的热演化控制。研究人员将使用手头的样品来生成两个综合的，沿ARC N和δ15N数据集，从而检查矿物质中的流体夹杂物与Cava和SVZ沿着Mafic Arc熔岩分离。由于这些系统在热相似，但具有不同的N来源和俯冲动力学，因此这些数据允许通过俯冲带和火山弧进行N回收的地质控制分离。 N2/3HE和N2/AR的比率将沿这些电弧段限制N通量，而Δ15N将允许源歧视。该项目利用了NU贵族人力资源质量质量光谱仪的独特分析能力，该分析能力仪与WHOI的专用样本粉碎和N纯化线有关，避免了现代气氛中的样本污染，并提供了当前可用的最高精度俯冲区n目前可用的数据。这一奖项反映了NSF的法定任务和审查的范围，这是通过评估的范围来弥补的。