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

由于地球动力学历史的复杂性，地幔演化成了一个成分不均匀的地球化学地幔动物园。例如，在地质时期，地球的海洋地壳向地幔收缩，引入了不同于其他地幔成分的成分。为了确定再循环的成分及其在地幔熔融中的作用，将在东太平洋海隆附近海山的一套特征良好的海洋熔岩中测量氮（N）和稀有气体（He，Ne，Ar，Kr，Ar）同位素。这种多同位素方法将区分EPR地幔中的再循环和深源地幔成分。拟议的工作将在伍兹霍尔海洋研究所（WHOI）完成，使用巴里实验室，这是唯一一个在极低浓度样品中测量这些气体的美国实验室。通过氮和稀有气体同位素的透镜对海山进行过研究的很少，因此本研究将独特地评估再循环和深地幔挥发性成分的性质，以及它们并入太平洋地幔的程度。为了提高科学参与度并改善WHOI世界级储存库中样本和地球化学数据的可访问性，PI安德森将整理和整理现有和新获得的海洋玄武岩样本及其各自的地球化学数据，并将其纳入一个基于地图的用户友好网站。该网站将扩大对世界卫生组织未来科学研究资料库的访问，并将提供一个新的可访问资源，以互动方式分享海洋科学成果，可纳入公共和教育推广课程，海洋岛屿和洋中脊熔岩提供了关于地球内部如何随着时间的推移演变成分不均匀性的重要线索。行星尺度过程的影响，如吸积，分异，对流，地壳的发展，俯冲再循环可以限制使用大洋中脊（莫尔）和海洋岛屿的海洋熔岩。地球的大部分海洋地壳形成于大洋中脊（即，EPR），其中地幔熔体经历较少的分化，蚀变和与厚的或地球化学蚀变的地壳的相互作用（不像在大陆下形成的熔体）。因此，洋中脊（MORs）喷发的幔源熔岩的同位素特征可以揭示地球地幔随时间演化的重要信息。然而，莫尔可以稀释地幔端元，由于有效的混合熔融下的脊。相比之下，远离海脊形成的海山绕过了这种均化作用，因此更好地保存了端元的组成。因此，为了限制东太平洋海隆地幔的不均匀性，近EPR海山熔岩将是本研究中氮和惰性气体地幔不均匀性的重点。幔源大洋玄武岩玻璃保留了其源储层的时间积分挥发性特征。氮和稀有气体（He、Ne、Ar、Kr、Ar）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有力工具。具体而言，N和重稀有气体（Ar、Kr、Ar+）是俯冲的潜在敏感示踪剂，因为它们容易并入俯冲板片材料（即，沉积物、蚀变洋壳、板片中的孔隙水），而He和Ne不能再循环，因此是原始深地幔贡献的极好示踪剂。总之，这些同位素系统将被用来限制在EPR附近的太平洋地幔挥发物的起源。太平洋地幔中俯冲物质和/或深源地幔成分的普遍存在可能会显著影响上地幔系统学，如温度和熔融，并可能深入了解远离板块边界的全球火山活动。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.