MARGINS: Collaborative Research: Experimental Investigation of Water Solubility in Arc Magmas at Upper Mantle Conditions

智力上的功绩。普遍认为，橄榄岩的部分熔融是从俯冲的大洋岩石圈的挥发物(主要是H2O)流入地幔楔体的底部开始的。然而，目前尚不清楚这些挥发物是通过水溶液、含水硅酸盐熔体、超临界相还是它们的某种组合输送到地幔楔形中的。此外，部分熔融在地幔楔体中进行的机制仍然是一个有争议的问题。在会聚边缘产生熔体的潜在模式包括形成小的、低密度的底辟，这些底辟通过楔形构造上升，并由于减压和加热的组合而部分熔化，或者当熔体通过地幔楔形向上渗入时，相对较冷的富含H2O的岩浆与较热的橄榄岩之间发生反应。部分熔体中溶解的H2O浓度及其对熔体在地幔中的液相线温度、密度、粘度和输运的影响是理解弧岩浆作用的关键。虽然有大量文献与地壳P-T条件下H2O在硅酸盐熔体中的溶解度有关，但与上地幔条件有关的实验数据并不存在。这反映了在固体介质活塞气缸装置上进行相关实验的难度。这项建议描述了一种新的实验方法，即用离子微探针测量固体矿物容器中的羟基浓度，并将其用作共存熔体中水浓度的替代。这种方法消除了直接分析硅酸盐熔体的需要，这在历史上是不可能的，因为在实验运行产品冷却过程中，由于快速形成淬火晶体和挥发损失。这些实验的结果将提供必要的数据，以量化从俯冲的大洋岩石圈到地幔楔的物质通量，以及涉及地幔楔内熔体产生和运输的过程--这两项都是边缘俯冲工厂倡议的目标。此外，这些数据将有助于解释伊豆-博宁-马里亚纳和中美洲俯冲系统边缘焦点地点的地球化学和地震结果。拟议的研究将(1)在促进教学、培训和学习的同时促进发现和理解，(2)扩大代表不足的群体的参与，以及(3)通过参与麻省理工学院/世界卫生组织联合计划的研究生、参加世界卫生组织暑期和少数族裔学生伙伴计划的本科生以及DTM的一名女性博士后研究员来加强研究和教育的基础设施。博士后将花时间在WHOI学习实验技术，并将帮助WHOI实施DTM开发的SIMS分析技术。

Intellectual Merit. It is generally accepted that partial melting of peridotite is initiated at the base of the mantle wedge by an influx of volatiles (primarily H2O) from the subducted oceanic lithosphere. However, it is unclear whether these volatiles are transported into the mantle wedge by an aqueous fluid, a hydrous silicate melt, a supercritical phase, or some combination thereof. Further, the mechanism by which partial melting proceeds in the mantle wedge remains a matter of debate. Potential modes for melt generation at convergent margins include the development of small, low-density diapirs that rise through the wedge and partially melt due to a combination of decompression and heating or reaction between relatively cool, H2O-rich magma and hotter peridotite as the melt percolates upward through the mantle wedge. The concentration of H2O dissolved in partial melts, and its influence on liquidus temperatures, densities, viscosities and transport of melts in the mantle are critical to understanding arc magmatism. While there is an extensive body of literature relating to the solubility of H2O in silicate melts at crustal P-T conditions, such experimental data pertaining to upper mantle conditions do not exist. This reflects the difficulty of doing the relevant experiments in a solid-medium piston cylinder device. This proposal describes a new experimental approach in which the concentration of hydroxyl in a solid mineral container will be measured by ion microprobe and used as a proxy for the concentration of water in the coexisting melt. This approach obviates the need to analyze the silicate melt directly, which historically has been precluded due to rapid formation of quench crystals and volatile loss during cooling of experimental run products. Results from these experiments will provide data necessary for quantifying the flux of material from the subducted oceanic lithosphere to the mantle wedge as well as the processes involved in melt generation and transport within the mantle wedge - both of which are goals of the MARGINS Subduction Factory initiative. Further, these data will help to provide a framework for interpreting geochemical and seismic results from MARGINS Focus Sites in the Izu-Bonin-Mariana and Central American subduction systems.Broader Impacts. The proposed research will (1) advance discovery and understanding while promoting teaching, training and learning, (2) broaden participation of underrepresented groups, and (3) enhance infrastructure for research and education through the involvement of graduate students in the MIT/WHOI Joint Program, undergraduate students participating in the WHOI Summer and Minority Student Fellow programs, and a female Postdoctoral Fellow at DTM. The post-doc will spend time at WHOI learning experimental techniques and will help WHOI implement SIMS analytical techniques that have been developed at DTM.