Linked Isotopic (Cl, O, H) and Petrologic Studies of Fluid-rock Interaction During the Subduction Cycle

“这个奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。”智力价值：地球科学中尚未解决的悖论之一是流体辅助的质量传递如何在收敛的板块边界发生。俯冲作用导致下行板和并置岩石中的P-T快速变化，这些岩石具有非常不同的地球化学特征。许多研究记录了板块俯冲过程中小而不均匀的流体通量，但弧状岩浆证明了板块与上覆地幔楔体之间的有效质量转移。这一表面上的悖论在很大程度上可以通过两种可能的方式解决：要么必须在100公里深处几乎完全完成质量传递，要么小体积流体的局部迁移对俯冲带旋回至关重要。我们请求支持开展一系列相互关联的领域和分析研究，以记录如何在俯冲系统的不同部分，包括高压和超高压岩石和交代地幔物质中实现小规模的流体-岩石沟通。次要成果将是更好地描述系统不同部分的氯-氧-氢同位素储集层。通过结合强亲水性示踪剂氯、氢氧同位素数据和岩石学观察，将解决不同尺度上的流体迁移问题。因为在变质去挥发或渗入过程中，氯的同位素分馏应该很少或没有，所以d37Cl值应该保存整个俯冲旋回中流体来源的记录。通过将d37Cl值与来自岩性单元沿线和跨岩性单元的采样横断面的d18O和Dd数据相耦合，将跟踪流体-岩石相互作用和反应的特定时期。全岩和微探头数据，以及流体包裹体分析，也将用于跟踪与特定流体释放或渗透事件相关的小规模传质过程。阿尔卑斯山的特定区域被选为深俯冲洋壳(Zermatt-Saas/Piemonte带)、俯冲大陆片(Sesia带)和亏损与交代地幔楔形岩(伊夫雷亚带的巴尔穆西亚体和Finero橄榄岩体)的代表。尽管在阿尔卑斯山造山作用期间，这些地点从来不是单一俯冲系统的一部分，但它们确实在相对有限的地理区域内提供了相关岩石类型的特殊特征暴露。仔细记录现场关系，再加上对所有样品进行详细的岩石学分析，将使同位素数据能够在背景下得到解释。在变质脱挥发分(如蛇纹岩破裂)主要幕之间的P-T间期，小尺度过程可能主导大尺度过程，并可能在改变地幔楔体的浅层中发挥关键作用。俯冲环境中的小规模流体-岩石相互作用对研究不同深度的地震成核过程也具有潜在的重要意义。这项研究将通过限制俯冲系统不同部分流体-岩石相互作用的具体机制来补充日益增长的大规模地球化学循环数据。广泛影响：该项目将有助于培训两名(女性)研究生，学习国际野外工作、稳定同位素地球化学、岩石学、微结构表征和全岩地球化学技术。这两名研究生还将在他们在UNM任职期间获得至少一次岩石学教学助理的经验和密切的指导。每年至少有一名本科生也将参与该项目，从而产生至少两篇高级论文。UNM的稳定同位素实验室因开发了氯同位素分析等新程序而得到广泛认可，该项目将使新的人员能够接受这些程序方面的培训，并有助于进一步的技术开发。样品将提供给其他研究人员，用于未来涉及其他微量元素和同位素系统的工作(样品特征将在网上公布)。这两个私人助理都经常将他们目前研究的各个方面纳入本科生和研究生的课堂，而且都有很好的学生指导记录。该项目将加强UNM与意大利和德克萨斯大学的同事之间的联系，并将促成这些机构之间今后的访问和交流，以及实验室的交叉校准。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual merit: One of the unsolved paradoxes in the earth sciences is how fluid-assisted mass transfer occurs at convergent plate boundaries. Subduction causes rapid P-T changes in the downgoing slab and juxtaposes rocks of very different geochemical characteristics. Many studies have documented small and heterogeneous fluid fluxes during slab subduction, yet arc magmas show evidence for effective mass transfer between the slab and the overlying mantle wedge. This apparent paradox can be largely resolved in two possible ways: either mass transfer must be accomplished almost entirely at depths 100 km, or localized migration of small fluid volumes is of fundamental importance to subduction zone cycling. We request support for a series of linked field and analytical studies aimed at documenting how small-scale fluid-rock communication is accomplished in different parts of the subduction system, including high- and ultrahigh-pressure rocks and metasomatized mantle material. A secondary outcome will be better characterization of Cl-O-H isotopic reservoirs in different parts of the system. Fluid migration at different scales will be addressed by combining a strongly hydrophilic tracer, chlorine, with oxygen and hydrogen isotopic data and petrologic observations. Because there should be little to no isotopic fractionation of chlorine during metamorphic devolatilization or infiltration, d37Cl values should preserve a record of fluid sources throughout the subduction cycle. By coupling d37Cl values with d18O and dD data from sampling transects along and across lithologic units, specific episodes of fluid-rock interaction and reaction will be tracked. Whole rock and microprobe data, along with fluid inclusion analyses, will also be used to track small-scale mass transfer processes associated with specific fluid release or infiltration events. Specific field areas in the Alps have been selected as representative of deeply subducted oceanic crust (Zermatt-Saas/Piemonte zone), subducted continental flake (Sesia Zone), and depleted vs. metasomatized mantle wedge rocks (Balmuccia and Finero peridotite bodies in the Ivrea Zone). Although these sites were never part of a single subduction system during the Alpine orogeny, they do provide exceptionally well-characterized exposures of relevant rock types within a relatively restricted geographic area. Careful documentation of field relations coupled with detailed petrologic analysis on all samples will allow isotopic data to be interpreted in context. Small-scale processes are likely to dominate over large-scale ones over P-T intervals between major episodes of metamorphic devolatilization (such as serpentine breakdown), and may play a key role in modifying shallow levels of the mantle wedge. Small-scale fluid-rock interaction in subduction settings is potentially also important to studies of earthquake nucleation processes at a variety of depth. This study will complement the growing body of data on large-scale geochemical cycling by placing constraints on specific mechanisms of fluid-rock interaction in different parts of the subduction system.Broader Impacts: This project will contribute to the training of two (female) graduate students in international fieldwork, stable isotope geochemistry, petrography, microstructural characterization, and whole-rock geochemical techniques. Both graduate students will also gain experience and close mentoring as teaching assistants in petrology at least once during their tenure at UNM. At least one undergraduate student per year will also be involved in the project, resulting in at least two senior theses. The stable isotope laboratory at UNM is widely recognized for its development of new procedures, such as chlorine isotope analysis, and this project will allow new personnel to be trained in these procedures, as well as contributing to further technique development. Samples will be made available to other researchers for future work involving other trace element and isotopic systems (sample characteristics will be posted online). Both PIs routinely incorporate aspects of their current research into undergraduate and graduate classes, and both have strong records of student mentoring. The project will strengthen ties between UNM and colleagues in Italy and at the University of Texas, and will lead to future visits and exchanges between these respective institutions, as well as laboratory cross-calibration.