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

智力优势。一般认为，橄榄岩的部分熔融是由俯冲洋壳岩石圈中挥发分（主要是H2O）的流入在地幔楔底部开始的。然而，目前还不清楚这些挥发物是否被输送到地幔楔的含水流体，含水硅酸盐熔体，超临界相，或它们的一些组合。此外，地幔楔部分熔融的机制仍然是一个争论的问题。在会聚边缘的熔体生成的潜在模式包括小，低密度底辟的发展，通过楔和部分熔融上升，由于减压和加热或反应之间的组合相对较冷，富H2O的岩浆和较热的橄榄岩的熔体向上通过地幔楔膨胀。溶解在部分熔体中的H2O的浓度及其对地幔熔体的液相线温度、密度、粘度和输运的影响是理解弧岩浆作用的关键。虽然有大量的文献涉及在地壳P-T条件下硅酸盐熔体中H2O的溶解度，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缸装置中进行相关实验的难度。该建议描述了一种新的实验方法，其中固体矿物容器中的羟基浓度将通过离子探针测量，并用作共存熔体中的水浓度的代理。这种方法避免了直接分析硅酸盐熔体的需要，这在历史上由于骤冷晶体的快速形成和实验运行产品冷却期间的挥发损失而被排除。从这些实验的结果将提供必要的数据，量化的物质从俯冲的海洋岩石圈地幔楔的流量，以及在地幔楔内的熔融生成和运输过程中所涉及的-这两个目标的边缘俯冲工厂倡议。此外，这些数据将有助于提供一个框架，解释地球化学和地震结果的边缘重点网站在伊苏-小笠原-马里亚纳和中美洲俯冲系统。拟议的研究将（1）推进发现和理解，同时促进教学，培训和学习，（2）扩大代表性不足的群体的参与，（3）通过研究生参与麻省理工学院/WHOI联合计划，本科生参与WHOI暑期和少数民族学生研究员计划，以及DTM的女性博士后研究员，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开发的西姆斯分析技术。

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.