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

俯冲带是地球上构造板块汇聚的区域。这些地区是地球上地质活动最活跃的地区之一，表现为火山活动和地震活动的高发率（例如，环太平洋火山带）。它们是地球上无处不在的特征，代表了我们星球内部和外部之间最广泛的元素循环系统。发生在俯冲带的过程涉及来自不同来源的大量流体，这些流体改变了从地表到100公里深处的化学成分和周围岩石的组成。目前的项目旨在更好地约束这些流体的来源和路径，以及它们在俯冲带过程（如岩石-流体相互作用和火山作用）中的作用。该项目将由地球科学中代表性不足的群体的教师以及来自纽约地区少数族裔服务机构的影响学生进行。蛇纹岩是由含水流体对地幔的蚀变作用形成的，含水高达14wt . %，是俯冲带过程中流体-岩石相互作用的最重要记录之一。因此，它是研究会聚板块边界内含水流体来源和作用的重要矿物。最近基于硼（一种流体流动元素）的研究表明，在缝合带发现的蛇纹岩记录了主要发生在：(i)俯冲板块，（ii）地幔楔，（iii）水合前弧的过程。因此，缝合带中的蛇纹岩代表了可追踪的最大的来自不同来源的导致地幔交代的含水流体记录。虽然两种主要流体端元（海水和高压变质流体）在B同位素方面具有很好的特征，但对于这些流体在俯冲过程中如何随着P和T的变化而混合、叠印和演化却知之甚少。本研究的主要目的是利用B同位素和B含量表征缝合线带蛇纹岩中流体混合/套印和二次过程。我们的研究将为俯冲过程中发生的脱水/（再）水化过程提供更好的图像。此外，这些数据对于理解流体在引发深部地震中的作用以及更好地约束导致俯冲带地幔熔融的流体是必要的。该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。

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.