Halogen Budget of Subducted Eclogites: The In-situ Perspective

卤素元素，如氟和氯，在各种地球系统中发挥着基本作用。它们影响全球气候、火山喷发、生物圈特性和地球深处物质的力学行为。尽管地震和火山灾害与这些元素在流体和矿物相中的丰度和分布有关，但在地球内部卤素的预算和通量方面仍存在严重差距。特别是，在富含海水的构造板块俯冲过程中，深度回收的卤素的数量仍然存在很大的不确定性，这一过程目前发生在世界各地55,000公里的海沟沿线。要研究俯冲构造板块的预算及其对地震和火山灾害的影响，最好的岩石样本是被称为榴辉岩的俯冲海洋板块的类似物。然而，对俯冲榴辉岩的卤素分析历来受到技术挑战的阻碍，限制了我们正确确定地球上卤素通量的能力。在这里，我们提出了一种先进的分析和成像技术的新组合，以提供对俯冲板块的卤素预算的独特限制。目标是回答以下问题：卤素如何分布在俯冲板块中，以及它们的分布如何影响与世界各地俯冲带有关的社会危害？该项目将为来自STEM代表性不足群体的学生提供在伍兹霍尔工作的实习机会，并为首席研究员的外展工作提供机会。大洋板块在大洋中脊形成，并在俯冲带深处回收，将大量卤素带回地球--S地幔。以前的研究在理解俯冲板块中发生的脱水和熔融反应方面取得了重大进展，但对元素通量的估计仍然存在很大争议。特别是，尽管对卤素的大量测量为元素循环提供了有价值的信息，但晶体颗粒、晶界、流体包裹体和早期蚀变的贡献无法通过这一技术区分开来，并可能导致对地球上卤素通量的严重歪曲估计。在这里，我们建议利用伍兹霍尔海洋研究所离子微探测器设施的PI领导的最新技术发展，首次提供俯冲榴辉岩中卤素的现场分布图。我们将使用一种新的技术组合-原位SIMS、显微CT扫描、离子色谱、热解-来量化代表世界各地各种俯冲条件的榴辉岩样品中的晶体颗粒、晶界、流体包裹体和早期蚀变的贡献。利用这些地区的新鲜样品和表征良好的样品，我们将确定卤素在俯冲带中的分布可能如何变化，并计算新的卤素通量。这一技术组合以前从未被提出过，是对历史上使用的整体方法的高度补充，并将提供对俯冲带卤素通量的关键洞察。PI将参与WHOI计划，该计划为来自代表性不足群体的学生提供实习机会。该奖项反映了NSF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。

Halogen elements, such as fluorine and chlorine, play a fundamental role in a variety of Earth systems. They influence global climate, volcanic eruptions, biosphere properties, and the mechanical behavior of deep Earth materials. Although earthquake and volcanic hazards are linked to the abundance and distribution of these elements in fluid and mineral phases, critical gaps exist regarding the budgets and fluxes of halogens in the Earth's interior. In particular, large uncertainties remain on the quantities of halogens that are recycled at depth during subduction of seawater-rich tectonic plates, a process that currently occurs along 55,000 km of oceanic trenches worldwide. The best rock samples to study the budget of subducted tectonic plates, and their consequences on earthquake and volcanic hazards, are analogs of subducted oceanic plates called eclogites. However, halogen analyses of subduction-derived eclogites have been historically hampered by technical challenges, limiting our ability to correctly define halogen fluxes on Earth. Here we propose a novel combination of advanced analytical and imaging techniques to provide unique constraints on the halogen budget of subducting plates. The goal is to answer the following questions: how are halogens distributed in subducted plates, and how does their distribution influence societal hazards linked to subduction zones worldwide? The project will provide an opportunity for an internship for a student from a STEM-underrepresented group to work at Woods Hole and outreach efforts by the principal investigator.Oceanic plates are created at mid-ocean ridges and recycled at depth in subduction zones, carrying back large amounts of halogens into the Earth?s mantle. Previous studies have made significant advances in understanding the dehydration and melting reactions that take place in subducting plates, but estimates of elemental fluxes remain largely debated. In particular, although bulk measurements of halogens provide valuable information into elemental cycling, the contributions from crystal grains, grain boundaries, fluid inclusions and incipient alteration cannot be distinguished through that technique and can lead to severely skewed estimates of halogen fluxes on Earth. Here we propose to take advantage of recent technical developments led by the PI at the Woods Hole Oceanographic Institution ion microprobe facility to provide, for the first time, an in-situ distribution map of halogens in subducted eclogites. We will use a novel combination of techniques - in-situ SIMS; micro-CT scanning; ion chromatography; pyrohydrolysis - to quantify the contribution from crystal grains, grain boundaries, fluid inclusions and incipient alteration in eclogite samples representative of various subduction conditions worldwide. Using fresh and well-characterized samples from these localities, we will determine how halogen distribution may vary in subduction zones and calculate new halogen fluxes. This combination of techniques has never been proposed before, is highly complementary to bulk approaches that have been historically used, and will provide critical insight into halogen fluxes in subduction zones. The PI will participate in a WHOI program that provides internships for students who are from underrepresented groups.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.