Postdoctoral Fellowship: OCE-PRF: Constraining recycled components in the Pacific mantle using nitrogen and noble gas isotopes

博士后奖学金：OCE-PRF：使用氮气和稀有气体同位素限制太平洋地幔中的回收成分

• 批准号: 2308183
• 负责人: Molly Anderson
• 金额: $ 34.33万
• 依托单位: Woods Hole Oceanographic Institution
• 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: 2023-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2308183&HistoricalAwards=false
• 关键词: Postdoctoral; Fellowship; OCE; PRF; Constraining

Due to the complex geodynamic history of Earth, its mantle has evolved to be compositionally heterogeneous, containing several distinct components which together comprise the "geochemical mantle zoo". For example, over geologic time, Earth’s oceanic crust recycles into the mantle, introducing compositions that differ from other mantle components. To identify recycled components and their role in mantle melting that produces most of Earth’s crust today, nitrogen (N) and noble gas (He, Ne, Ar, Kr, Xe) isotopes will be measured in a suite of well-characterized oceanic lavas from seamounts near the East Pacific Rise (EPR). This multi-isotope approach will discriminate between recycled and deeply sourced mantle components in the EPR mantle. The proposed work will be completed at Woods Hole Oceanographic Institution (WHOI), using The Barry Lab, the only USA-based lab measuring these gases in extremely low concentration samples. Very few seamounts have been examined through the lens of N and noble gas isotopes, so this study will uniquely assess the nature of recycled and deep mantle volatile components, and the extent to which they are incorporated into the Pacific mantle. To increase participation in science and improve the accessibility of samples and geochemical data from WHOI’s world-class repository, PI Anderson will curate and collate existing and newly-acquired ocean basalt samples and their respective geochemical data into a map-based, user-friendly website. The website will broaden access to WHOI’s repository for future scientific research, and will provide a new accessible resource for sharing ocean science results in an interactive way that can be incorporated into public and educational outreach curriculum.Ocean island and mid-ocean ridge lavas provide important clues about how Earth’s interior has evolved compositional heterogeneities over time. The influence of planet-scale processes like accretion, differentiation, convection, development of a crust, and subduction recycling can be constrained using oceanic lavas from mid-ocean ridges (MOR) and ocean islands. Most of Earth’s oceanic crust forms at mid-ocean ridges (i.e., the EPR), where mantle melts undergo less differentiation, alteration, and interaction with thick or geochemically altered crust (unlike melts forming beneath continents). Isotopic characterization of mantle-derived lavas erupted at mid-ocean ridges (MORs) can therefore reveal important information about the evolution of Earth’s mantle over time. However, MOR can dilute mantle end members due to efficient mixing of melts beneath the ridge. By contrast, seamounts forming away from the ridge by-pass this homogenization and thus better preserve end-member compositions. Therefore, to constrain mantle heterogeneity beneath the East Pacific Rise, near-EPR seamount lavas will be the focus of N and noble gas mantle heterogeneity in this study. Mantle-derived oceanic basalt glasses preserve time-integrated volatile characteristics of their source reservoir. Nitrogen and noble gas (He, Ne, Ar, Kr, Xe) isotopes vary systematically between mantle, crustal, and atmosphere reservoirs, making them powerful tools for tracing interactions between Earth’s surface and interior. Specifically, N and heavy noble gases (Ar, Kr, Xe) are potentially sensitive tracers of subduction, because they are readily incorporated into subducting slab materials (i.e., sediments, altered oceanic crust, pore water in the slab), whereas He and Ne are not recycled and are thus excellent tracers of primordial deep mantle contributions. Together, these isotope systems will be used to constrain the origin of volatiles in the Pacific mantle near the EPR. The prevalence of subducted materials and/or deeply sourced mantle components in the Pacific mantle may significantly impact upper mantle systematics like temperature and melting, and may lend insight into global volcanic activity away from plate boundaries.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.

由于地球复杂的地球动力学历史，它的地幔已经演化成成分不同的异质，包含几个不同的成分，共同构成了“地球化学地幔动物园”。例如，随着地质时间的推移，地球的洋壳循环进入地幔，引入了与其他地幔成分不同的成分。为了确定再循环的成分及其在地幔熔融中的作用，地幔熔化产生了当今地球的大部分地壳，将在东太平洋隆起(EPR)附近海山的一套特征良好的海洋熔岩中测量氮(N)和惰性气体(He、Ne、Ar、Kr、Xe)同位素。这种多同位素方法将区分EPR地幔中的再循环和深来源的地幔成分。拟议中的工作将在伍兹霍尔海洋研究所(WHOI)完成，使用巴里实验室，这是唯一一个测量极低浓度样品中这些气体的美国实验室。通过N和稀有气体同位素透镜检查的海山很少，因此这项研究将独特地评估再循环和深部地幔挥发性组分的性质，以及它们被并入太平洋地幔的程度。为了增加对科学的参与，并改善从世界卫生组织世界级信息库获取样品和地球化学数据的可及性，Pi Anderson将整理和整理现有的和新获得的海洋玄武岩样品及其各自的地球化学数据，并将其纳入一个以地图为基础的、用户友好的网站。该网站将扩大对世界卫生组织未来科学研究储存库的访问，并将提供一个新的可访问资源，用于以互动方式分享海洋科学成果，并可纳入公共和教育推广课程。大洋岛和大洋中脊熔岩提供了关于地球内部如何随着时间的推移演化成分不均一性的重要线索。利用来自大洋中脊(MOR)和海洋岛屿的大洋熔岩，可以限制行星尺度过程的影响，如吸积、分化、对流、地壳发展和俯冲再循环。地球的大部分洋壳形成在大洋中脊(即EPR)，地幔熔体在那里经历较少的分异、蚀变和与厚的或地球化学改变的地壳的相互作用(不像大陆下形成的熔体)。因此，在大洋中脊(MORS)喷发的地幔岩浆的同位素特征可以揭示有关地球地幔随时间演化的重要信息。然而，由于熔体在山脊下的有效混合，MOR可以稀释地幔末端成员。相比之下，离开海脊形成的海山绕过了这种均化，因此更好地保存了终端成员的组成。因此，为了限制东太平洋隆起之下地幔的不均一性，近EPR海山熔岩将是本研究中N和稀有气体地幔不均质性的重点。地幔成因的大洋玄武岩玻璃保存了源岩储层随时间变化的挥发性特征。氮和惰性气体(He、Ne、Ar、Kr、Xe)同位素在地幔、地壳和大气层之间有系统的变化，使它们成为追踪地球表面和内部之间相互作用的强大工具。具体地说，N和重惰性气体(Ar、Kr、Xe)是潜在的敏感俯冲示踪剂，因为它们很容易被并入俯冲板片物质(即沉积物、蚀变洋壳、板片中的孔隙水)，而He和Ne不再循环，因此是原始深部地幔贡献的良好示踪剂。总而言之，这些同位素系统将被用来限制EPR附近太平洋地幔中挥发物的来源。太平洋地幔中俯冲物质和/或深源地幔成分的盛行可能会显著影响上地幔系统学，如温度和融化，并可能有助于洞察远离板块边界的全球火山活动。这一奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。