Collaborative Research: Mantle metasomatism during serpentinization in subduction zones: Insights from in-situ boron isotopes

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Subduction zones are regions of our planet where tectonic plates converge. These regions are among the most geologically active on Earth, expressed by high rates of volcanism and seismicity (e.g., the Pacific Ring of Fire). They are ubiquitous features on Earth and represent the most extensive element recycling system between the interior and exterior of our planet. The processes occurring in subduction zones involve an enormous amount of fluids from different sources, which change the chemistry and alter the composition of the surrounding rocks from the surface to depths of ~100 km. The present project aims to better constrain the source(s) and paths of these fluids, as well as their role on subduction zone processes such as rock-fluid interaction and volcanism. This project will be carried out by faculty that belong to underrepresented groups in geosciences as well as impact students from a minority-serving institution in the NYC area.Serpentine forms by alteration of the mantle by aqueous fluids and contains up to 14 wt. % of water, making it one of the most important records of fluid-rock interactions in subduction zone processes. Therefore, it represents a critical mineral to study the source and role of aqueous fluids within convergent plate boundaries. Recent studies based on boron (a fluid mobile element) suggest that serpentinites found in suture zones record processes that occurred mainly in: (i) the subducting slab, (ii) the mantle wedge, (iii) the hydrated forearc. Thus, serpentinites in suture zones represent the largest trackable record of aqueous fluids responsible for mantle metasomatism from different sources. Although the two main fluid endmembers in terms of B isotopes (seawater and high-pressure metamorphic fluids) are well-characterized, little is known about how these fluids mix, overprint, and evolve with the changes in P and T during subduction. The main goal of this study is to characterize fluid mixing/overprinting and secondary processes occurring in serpentinites collected in suture zones, using B isotopes and B contents. Our study will provide a better picture of the dehydration/(re)hydration processes occurring during subduction. Additionally, these data are necessary to understand the role of fluid(s) in triggering deep earthquakes and better constrain the fluid(s) responsible for mantle melting in subduction zones.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.