Tracing Evidence of Fluid Flow in Eclogite, Blueschist and Amphibolite Blocks in Subduction Zone Melanges

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”知识价值——俯冲带的流体流动对弧岩浆的产生、大陆地壳的形成、地幔的地球化学演化以及贝尼奥夫带地震活动的产生有着广泛的影响。然而，关于俯冲过程中流体释放和传质的性质，仍然存在许多悬而未决的问题，包括流体成分如何变化以及脱水板块的流体通量如何随深度的增加而变化。古俯冲带的流体-岩石相互作用在msamuanges发现的高品位块体中留下了各种尺度的化学和矿物学特征。对来自CA Franciscan杂岩的此类岩石的详细岩石学和地球化学研究表明，在块状壳层和蓝片岩层中，流体逆行渗透、低Li浓度和高_7Li之间存在关系（pennton - dorland et al., 2008）。Li同位素变化记录了短空间尺度上不同程度的流体入渗。作为该工作的延伸，本项目旨在建立三个加勒比俯冲带复合体（多米尼加共和国的萨马纳复合体、委内瑞拉的卡贝略港、科迪勒拉德拉科斯塔带和委内瑞拉的玛格丽塔岛）的高品位块体的顺行和逆行部分的综合地球化学特征（例如微量元素浓度、Sr、Nd和Li同位素组成）。根据俯冲-水道模型，高品位岩石沿板幔楔接触面形成于较深的区域，随后在该界面上以泥质或蛇纹岩质基质逆流而出。提出的研究将检验这样一种假设，即来自太平洋-加勒比型俯冲带的高质量m<s:1>蓝块体在岩石历史的逆行部分记录了来自下伏板块的流体的逆行通道化渗透。如果正确的话，可以预测由于俯冲板块浅部的流体较晚渗透，逆行岩石的Li浓度较低，而_7Li含量较顺行岩石高。此外，所获得的数据将有助于评估不同演化阶段[1]流体来源（如沉积物与玄武岩板）、区块内流体渗透[2]长度尺度以及流体渗透[3]类型（如扩散、平流）。总的来说，这项工作将为俯冲带流体-岩石相互作用的性质提供新的约束，从而更好地理解俯冲流体的作用。更广泛的影响-建议的研究的主要部分将由研究生和本科生在PI的指导下完成。因此，该项目包括岩石学和地球化学以及科学写作和通讯方面的训练的重要组成部分。这项工作可能会包括地球科学中代表性不足的群体。PI目前在她的研究小组中为两名女性提供建议：一名研究生和一名本科生。此外，去年，一名非裔美国女大学生通过美国国家科学基金会资助的马里兰大学LSAMP项目在PI的研究小组工作。此外，马里兰大学地质系要求其所有本科专业的学生完成一篇毕业论文，预计该项目将导致完成两篇毕业论文。此外，PI是一位最近才开始她的教授生涯的女性。为拟进行的研究提供资助将有助她的研究事业，并协助她建立一个强大的研究小组

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual merit - Fluid flow in subduction zones has broad affects the generation of arc magmas, the formation of continental crust, the geochemical evolution of the mantle, and the generation of Benioff zone seismicity. Yet many outstanding questions remain regarding the nature of fluid release and mass transfer during subduction, including how fluid compositions change and fluid fluxes from dehydrating slabs vary with increasing depth. Fluid-rock interactions in ancient subduction zones have left behind chemical and mineralogic signatures on a variety of scales in high-grade blocks found in mélanges. Detailed petrologic and geochemical investigations of such rocks from the Franciscan Complex, CA demonstrate a relationship between retrograde fluid infiltration, lower Li concentration and higher _7Li (Penniston-Dorland et al., 2008) in block rinds and blueschist layers. Li isotope variations record variable degrees of fluid infiltration on short spatial scales. As an extension of that work, this project aims to establish comprehensive geochemical characterization (e.g., trace element concentrations, and Sr, Nd and Li isotopic compositions) of prograde and retrograde portions of high-grade blocks from three Caribbean subduction zone complexes: the Samana Complex, Dominican Republic, Puerto Cabello, Cordillera de la Costa Belt, Venezuela, and Isla Margarita, Venezuela. According to the subduction-channel model, high-grade rocks form at great depth along the slab-mantle wedge contact and then are subsequently exhumed in an argillaceous or serpentinitic mélange matrix backflow up this interface. The proposed study will test the hypothesis that high-grade mélange blocks from Pacific-Caribbean-type subduction zones record retrograde channelized infiltration by fluids derived from the underlying slab during the retrograde portion of the rocks' histories. If correct, it is predicted that the retrograde rocks will record lower Li concentrations and higher _7Li relative to prograde rocks due to late infiltration of fluids emanating from shallow portions of the subducting slabs. In addition, the data obtained will allow assessment of [1] fluid sources (e.g., sediments vs. basaltic slab) at various evolutionary stages, [2] length scales of fluid infiltration within blocks, and [3 styles of fluid infiltration (e.g. diffusion, advection). Overall, this work will provide new constraints on the nature of fluid-rock interaction in subduction zones, hence, better understanding of the role of subduction fluids in general.Broader impacts - A major portion of the research proposed will be done by graduate and undergraduate students under the direction of the PI. Thus, the project includes a strong component of training in petrology and geochemistry, as well as in scientific writing and communication. This work will likely include underrepresented groups in the Earth Sciences. The PI currently advises two women in her research group: one graduate student and one undergraduate student. In addition, an African-American undergraduate woman worked in the PI's research group last year through the NSF-funded LSAMP program at UMd. Further, the Department of Geology at UMd requires all its undergraduate majors to complete a senior thesis, and it is anticipated that the project will result in the completion of two senior theses. In addition, the PI is a woman who has recently begun her professorial career. Provision of funding for the proposed research will advance her research career and assist her in building a strong research group