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

知识价值。人们普遍认为，橄榄岩的部分熔融是由俯冲的海洋岩石圈的挥发物（主要是H2O）流入地幔楔的底部引起的。然而，尚不清楚这些挥发物是通过含水流体、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中。此外，部分熔融在地幔楔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发育小的、低密度的底喷岩，这些底喷岩通过楔体上升，当熔体通过地幔楔向上渗透时，由于减压和加热的结合或相对较冷的富氢岩浆与较热的橄榄岩之间的反应，部分熔融。部分熔体中溶解水的浓度及其对地幔液温、密度、粘度和熔体输运的影响是了解弧岩浆活动的关键。虽然有大量的文献与地壳P-T条件下硅酸盐熔体中H2O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缸装置中进行相关实验的困难。本文提出了一种新的实验方法，用离子探针测量固体矿物容器中羟基的浓度，并将其作为共存熔体中水浓度的代表。这种方法避免了直接分析硅酸盐熔体的需要，由于在实验运行产品的冷却过程中快速形成淬火晶体和挥发性损失，这在历史上是被排除的。这些实验的结果将提供必要的数据，用于量化从俯冲的海洋岩石圈到地幔楔的物质通量，以及地幔楔内熔体产生和运输的过程——这两者都是边缘俯冲工厂计划的目标。此外，这些数据将有助于为解释伊豆-博宁-马里亚纳和中美洲俯冲系统边缘焦点点的地球化学和地震结果提供一个框架。更广泛的影响。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)扩大代表性不足群体的参与，以及(3)通过参与麻省理工学院/WHOI联合项目的研究生、参与WHOI夏季和少数民族学生奖学金项目的本科生以及DTM的一名女性博士后，加强研究和教育的基础设施。博士后将在WHOI学习实验技术，并将帮助WHOI实施在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.