Halogen Budget of Subducted Eclogites: The In-situ Perspective

点击翻译按钮获取中文摘要

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.