MARGINS: Collaborative Research: The Oxidation State of Mariana Arc Magmas and its Relationship to Subduction Volatile and Mass Cycling

合作研究：马里亚纳岛弧岩浆的氧化态及其与俯冲挥发物和质量循环的关系智力价值。地球内部和外部之间的地球化学交换，通过山脊处的地壳形成和俯冲带处的地壳破坏，随着时间的推移改变了地表和内部储层的组成。随着年龄的增长，洋壳逐渐氧化和水合，将俯冲板块中的水和氧化态联系起来。由于地幔的缓冲能力，这种联系可能会在俯冲带内解耦，或者可能持续到深处。来自俯冲板块的氧化或氧化成分可能会改变地幔和岩浆的氧化态，从而影响元素分配、岩浆分异和脱气，以及地幔中氧气可用性的长期演化。最近对氧化态的大块岩石和矿物学代理（例如氧化还原敏感的 V 分配、尖晶石成分、全岩 Fe 3/_Fe）的几项研究得出了现代构造环境和整个地球历史中地幔氧化态的矛盾观点。现代俯冲带为研究地幔和水圈的氧化还原条件是否以及如何共同演化提供了理想的环境。本研究旨在开发一种测量玄武岩浆氧化态的新方法，使用同步加速器微束技术 (micro-XANES) 对玻璃中氧化还原敏感的 Fe 3/_Fe 比率进行无损原位测量。该技术将允许直接比较熔体氧化态与原始的、未脱气的岩浆液体（即天然枕状玻璃和熔体包裹体）和实验玻璃中主要的、挥发性的和微量元素的组成，采样规模约为 10 微米。将分析来自马里亚纳弧/槽系统沿线和跨过马里亚纳弧/槽系统的天然玻璃和来自模拟活塞缸实验的合成玻璃，目的是（1）测试岩浆 Fe 3/_Fe 比率与熔体和地幔氧化态的替代指标（2）评估岩浆过程、挥发物和板片衍生成分在影响氧化态中的作用，以及（3）模拟俯冲循环对地球内部氧化还原条件长期演化的影响。马里亚纳弧熔岩是这项研究的理想选择，因为它们携带原始的、未脱气的玄武岩熔体包裹体，记录了一系列岩浆水含量和板片衍生的化学特征。此外，还可以分析来自马里亚纳海槽弧后盆地全长的海底玻璃样本，以提供有关挥发物含量和氧化状态空间变化的信息。更广泛的影响。该项目将开发一种潜在变革性的新型微分析技术，用于量化天然和实验玻璃中的氧化态。结果将通过同行评审的出版物和在线数据库传播。这些结果将产生广泛影响，与边缘、山脊和深层地球科学界直接相关。该项目还将促进两名职业生涯早期女性 PI 的职业发展，她们将发挥互补的技能来解决需要高度协作的多学科团队的新问题。这两位 PI 致力于指导地球科学领域代表性不足的少数群体，并在该项目的试点工作中与这些学生建立了良好的记录。最后，该奖项将资助博士学位。学生将由两位 PI 共同指导，从而接触到广泛的实验和分析技术，从而开启地球科学的职业生涯。

Collaborative Research: The oxidation state of Mariana arc magmas and its relationship to subduction volatile and mass cycling Intellectual Merit. Geochemical exchange between the earth's interior and exterior, via crust formation at ridges and crust destruction at subduction zones, has modified the composition of both the surface and interior reservoirs through time. The oceanic crust becomes progressively oxidized and hydrated as it ages, linking water and oxidation state in the subducting plate. This link could decouple within subduction zones due to the mantle's buffering capacity, or it may persist to depth. Oxidized or oxidizing components from the subducted slab may modify mantle and magmatic oxidation states, thereby influencing element partitioning, magmatic differentiation and degassing, and the long-term evolution of oxygen availability in the mantle. Several recent studies of bulk-rock and mineralogical proxies for oxidation state (e.g., redox-sensitive V partitioning, spinel composition, whole-rock Fe+3/_Fe) have yielded contradictory views of mantle oxidation state in modern tectonic settings and throughout earth history. Modern subduction zones provide an ideal setting to investigate if and how redox conditions of the mantle and hydrosphere have co-evolved. This study aims to develop a new method of measuring the oxidation state of basaltic magmas, using a synchrotron-based microbeam technique (micro-XANES) for non-destructive, in situ measurement of the redox-sensitive Fe+3/_Fe ratio in glasses. This technique will allow direct comparison of melt oxidation state to major, volatile, and trace element composition in primitive, undegassed magmatic liquids (i.e., natural pillow glasses and melt inclusions) and experimental glasses at a ~10 _m sampling scale. Both natural glasses from along and across the Mariana arc/trough system and synthetic glasses from analog piston-cylinder experiments will be analyzed, with the goals of (1) testing magmatic Fe+3/_Fe ratios against alternative proxies of both melt and mantle oxidation state (2) evaluating the role of magmatic processes, volatiles, and slab-derived components in influencing oxidation state, and (3) modeling the effects of the subduction cycle on the long-term evolution of redox conditions in the earth's interior. Mariana arc lavas are ideal for this study because they carry primitive, undegassed, basaltic melt inclusions that record a range of magmatic water contents and slab-derived chemical signatures. Also, samples of submarine glass from the full length of the Mariana trough back-arc basin, can be analyzed to provide information regarding spatial variations in volatile content and ozidation state. Broader Impacts. This project will develop a potentially transformative new micro-analytical technique for the quantification of oxidation state in natural and experimental glasses. Results will be disseminated through peer-reviewed publications and on-line databases. These results will have broad-reaching results with direct relevance to the MARGINS, RIDGE, and deep earth science communities. This project also will foster the careers of two early-career female PIs who will bring their complementary skills to bear on a new problem requiring a highly collaborative, multidisciplinary team. The two PIs are deeply committed to mentoring under-represented minorities in the earth sciences and have established a track record with such students during the pilot work for this project. Finally, this award will fund a Ph.D. student to be jointly mentored by the two PIs, and therefore exposed to a broad palate of experimental and analytical techniques with which to launch a career in the earth sciences.