Collaborative Research: MARGINS--The Relationship Between Water, Trace Elements and Slab Dehydration Across the Mariana and Izu-Bonin Arcs

智力上的功绩。水在俯冲带中的作用在很大程度上是根据B、BA、K、Rb和U等流动元素的行为来理解的，而不是直接根据对水的测量来理解的。这是因为对弧光的大多数研究都依赖于水下熔岩的数据，这些熔岩在脱气过程中遭受了挥发性损失。已发表的实验研究和中美洲弧区的熔体包裹体研究表明，水从弧区的板条上持续释放出来。这与流体活动元素的行为相反，流体活动元素逐渐从板块中剥离，并显示出系统的跨弧变化。这项研究的一个基本目的是评估水、微量元素以及氢和硼的稳定同位素在IBM系统的两个不同部分-马里亚纳弧和伊祖-博宁弧-之间的释放。这些地点有不同的倾角和俯冲速率，因此我们将确定这些物理参数是否对渐进性脱水过程中的流体行为有任何影响。这项研究的第二个目标是测试板坯流体的痕量元素和B同位素替代物如何跟踪向IBM地幔来源的流体输送，以及D/H和B同位素是否跟踪类似的流体释放过程，或者每个系统是否唯一地跟踪不同的脱水阶段。利用离子探针技术对海底熔岩玻璃和橄榄石包裹体中的挥发分(CO_2、H_2O、S、Cl、F)、液态元素(B、Cl、Ba、K、Rb等)和稳定同位素(H、B)进行了系统的研究。这项工作将得到对B同位素的多收集ICPMS分析以及主要元素的电子探针测量的补充。这些样品包括来自马里亚纳群岛的一套新的跨链火山，来自马里亚纳海槽的弧后熔岩和玻璃，以及来自伊祖-博宁弧后和弧后的熔岩。弧岩浆水含量与流体活动微量元素之间的相关性(或缺乏相关性)将对利用现有微量元素和同位素数据解释其他俯冲带的地球化学特征产生重要影响，但这些俯冲带的水含量尚未测量。该项目将补充正在进行的调查刘盆地熔融过程的MI研究，以及边缘俯冲工厂倡议的科学目标，并将促进美国和日本五个机构的科学家之间的合作。该项目将支持伍兹霍尔海洋研究所(WHOI)的一名女性早期职业科学家。作为WHOI和NSF-REU暑期实习生计划的一部分，PI将在项目的第二年指导一名本科生，向他们介绍离子微探针技术。这项工作还将引入新的分析方案，以帮助振兴NSF支持的WHOI离子探测器设施，该设施在2002年10月的一场火灾中遭到严重破坏。

Intellectual Merit. The role of water in subduction zones is largely understood based on behavior of fluid-mobile elements such as B, Ba, K, Rb and U, rather than on measurements of water directly. This is because most studies of arcs rely on data from subaerial lavas which have suffered volatile loss through degassing. Published experimental studies and melt inclusion studies across the Central American arc suggest that water is released continuously from the slab across the arc. This is contrary to the behavior of fluid mobile elements, which are progressively stripped from the slab and show systematic cross-arc changes. A fundamental aim of this study is to evaluate the release of water, trace elements, and stable isotopes of hydrogen and boron across two contrasting segments of the IBM system - the Marianas and the Izu-Bonin arcs. These sites have different dip angles and subduction rates, thus we will determine whether these physical parameters have any impact on fluid behavior during progressive dehydration. The second objective of this study is to test how well trace element and B-isotopic proxies for slab fluids track fluid delivery to IBM mantle sources, and whether D/H and B isotopes trace similar fluid release processes or whether each system uniquely traces different stages of dehydration. We propose a systematic study of volatiles (CO2, H2O, S, Cl, and F), fluid soluble elements (B, Cl, Ba, K, Rb and others) and stable isotopes (H, B) in glasses and olivine hosted melt inclusions (MIs) from submarine lavas using ion microprobe techniques. This work will be complemented by multicollector ICPMS analyses of B isotopes, as well as electron microprobe measurements of major elements. The samples include a new suite of cross-chain volcanoes from the Marianas, back-arc lavas and glasses from the Mariana Trough, and lavas from the Izu-Bonin arc and back-arc. The correlation (or lack thereof) between arc magma water contents and fluid-mobile trace elements will have an important impact on the interpretation of geochemical signatures at other subduction zones with existing trace element and isotopic data but where water contents have not yet been measured.Broader Impacts. This project will complement ongoing MI studies investigating the melting process in the Lau Basin, as well as the scientific objectives of the MARGINS Subduction Factory initiative, and will foster collaboration between scientists at five institutions in the US and Japan. The project will support a female early career scientist at Woods Hole Oceanographic Institution (WHOI). As part of a WHOI and NSF-REU summer intern programs, the PI will mentor an undergraduate student during the 2nd year of the project, introducing them to ion microprobe techniques. This work will also result introduce new analytical protocols to help revitalize the NSF-supported WHOI ion probe facility which was seriously damaged in a fire in October of 2002.