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地区。这些地区是地球上地质最活跃的地区之一，表现为火山活动和地震活动的高发率(例如，太平洋火环)。它们是地球上无处不在的特征，代表着地球内部和外部之间最广泛的元素循环系统。在俯冲带中发生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约100公里深的围岩的化学成分和成分。本项目旨在更好地约束这些流体的来源(S)和路径，以及它们在俯冲带过程中的作用，如岩石-流体相互作用和火山作用。该项目将由地学领域中代表性不足的教师以及来自纽约市地区一所少数族裔服务机构的学生进行。蛇纹岩是由水流体改变地幔形成的，含有高达14%的水，使其成为俯冲带过程中流体-岩石相互作用的最重要记录之一。因此，它是研究收敛板块边界内水流体的来源和作用的关键矿物。最近基于硼(一种流动元素)的研究表明，在缝合带中发现的蛇纹岩记录了主要发生在：(I)俯冲板，(Ii)地幔楔，(Iii)水化弧前的过程。因此，缝合带中的蛇纹岩代表了来自不同来源的负责地幔交代的水流体的最大可追踪记录。尽管B同位素方面的两个主要流体端元(海水和高压变质流体)已经得到很好的描述，但对于这些流体如何混合、叠加以及在俯冲过程中随着P和T的变化而演化的了解很少。这项研究的主要目的是利用B同位素和B含量表征缝合带中蛇纹岩中发生的流体混合/叠印和二次作用。我们的研究将更好地描绘俯冲过程中发生的脱水/(再)水合过程。此外，这些数据对于了解流体(S)在触发深部地震中的作用以及更好地约束负责俯冲带地幔融化的流体(S)是必要的。这一裁决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。

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.