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

“该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。“知识价值-俯冲带中的流体流动对弧岩浆的生成、大陆地壳的形成、地幔的地球化学演化和贝尼奥夫带地震活动的生成产生了广泛的影响。然而，许多悬而未决的问题仍然存在的流体释放和质量转移的性质，在俯冲过程中，包括流体成分的变化和流体通量从脱水板随深度的增加而变化。古代俯冲带中的流体-岩石相互作用在混杂岩中发现的高级块体中留下了各种尺度的化学和矿物学特征。对来自加利福尼亚州Franciscan Complex的此类岩石进行的详细岩石学和地球化学研究表明了逆行流体渗透、较低Li浓度和较高_7Li之间的关系（Penniston-Dorland等人，2008年）在块皮和蓝片岩层。锂同位素的变化记录不同程度的流体渗透在短的空间尺度。作为这项工作的延伸，该项目旨在建立全面的地球化学特征（例如，微量元素浓度和Sr，Nd和Li同位素组成）的高级块体的逆冲和逆行部分从三个加勒比俯冲带复合体：萨马纳复杂，多米尼加共和国，卡贝略港，科迪勒拉德拉科斯塔带，委内瑞拉和玛格丽塔岛，委内瑞拉。根据俯冲-水道模型，高级岩石形成于沿着板幔楔接触的大深度处，随后在泥质或蛇纹质混杂岩基质中被折返，沿该界面向上回流。拟议的研究将检验一种假设，即太平洋-加勒比型俯冲带的高级混杂岩块记录了在岩石历史的逆行部分期间来自下层板片的流体的逆行通道化渗透。如果正确的话，据预测，逆行岩石将记录较低的锂浓度和较高的_7锂相对于俯冲岩石由于后期渗透的流体从浅部的俯冲板。此外，获得的数据将允许评估[1]流体来源（例如，沉积物与玄武岩板片），[2]块体内流体渗透的长度尺度，[3]流体渗透的类型（例如扩散，平流）。总的来说，这项工作将提供新的约束条件的性质，流体-岩石相互作用的俯冲带，因此，更好地了解俯冲流体的作用一般。更广泛的影响-一个主要部分的研究建议将完成研究生和本科生的指导下，PI。因此，该项目包括岩石学和地球化学以及科学写作和交流方面的培训。这项工作可能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，一位非洲裔美国本科生去年通过NSF资助的UMD LSAMP项目在PI的研究小组工作。此外，UMD地质系要求其所有本科专业完成一篇高级论文，预计该项目将导致完成两篇高级论文。此外，PI是一名最近开始其教授生涯的女性。为拟议的研究提供资助将促进她的研究事业，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