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》(公共法律111-5)资助的。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，以及来自脱水板块的流体通量如何随着深度的增加而变化。古俯冲带中的流体-岩石相互作用在混杂岩中发现的高级地块中留下了不同尺度的化学和矿物学特征。对加州Franciscan杂岩的详细岩石学和地球化学研究表明，块体和蓝片岩层中的逆行流体渗透、低Li浓度和高7Li之间存在关系(Penniston-Dorland等，2008)。Li同位素变化记录了短空间尺度上不同程度的流体渗透作用。作为这项工作的延伸，该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Samana杂岩、委内瑞拉的卡贝洛港、委内瑞拉的科迪莱拉-德拉科斯塔带和委内瑞拉的玛格丽塔岛--高级地块的进退部分的全面地球化学特征(例如，微量元素浓度以及锶、钕和锂的同位素组成)。根据俯冲通道模型，高品位岩石沿着板幔楔形接触在很深的地方形成，随后以泥质或蛇纹岩质混杂岩基质沿该界面回流而出。这项拟议的研究将检验这样一种假设，即来自太平洋-加勒比海型俯冲带的高级混杂岩块在岩石历史的逆行部分记录了来自底部板岩的流体逆行沟道化的渗透作用。如果正确，可以预测，由于来自俯冲板块浅部的流体的晚期渗入，逆行岩石将记录到比前进岩石更低的Li浓度和更高的7Li。此外，获得的数据将允许评估不同演化阶段的[1]流体来源(例如，沉积物与玄武岩板块)，[2]区块内流体渗透的长度尺度，以及[3种流体渗透方式(例如，扩散、平流)。总体而言，这项工作将对俯冲带流体-岩石相互作用的性质提供新的限制，从而更好地理解俯冲流体的作用。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，一名非裔美国本科生通过NSF资助的UMD LSAMP项目在PI的研究小组工作。此外，UMD地质学系要求其所有本科生完成一篇高级论文，预计该项目将导致两篇高级论文的完成。此外，PI是一名最近开始她的教授生涯的女性。为拟议的研究提供资金将促进她的研究事业，并帮助她建立一个强大的研究团队

"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