SGER: Chlorine Isotopes as Tracers of Subduction Zone Fluids

知识价值。提出了一项概念验证研究，以评估稳定氯同位素丰度作为俯冲带衍生流体的新型地球化学示踪剂。PI开发了一种强大的分析方法，用于测定不同潜在储层（包括沉积物、孔隙水和蛇纹岩）的delta37Cl值，所有这些储层都具有不同的同位素组成。本文认为，无论是火山气体（如喷气孔），还是玻璃和火山灰，都应忠实地记录弧岩浆活动中流体的氯同位素组成。地表水的污染会使样品的delta37Cl值接近于零。关于富马酸气体的初步数据涵盖了超过10毫帕的范围，这一事实表明，这种影响是微乎其微的。将对已经有很好特征的中美洲火山弧的富马酸气体、火山玻璃和火山灰样品进行Cl同位素系统的确定，中美洲火山弧是边缘震源点之一。所有样品都在手中，技术已经完善，申请资助的博士后是氯同位素地球化学领域的专家，因此开展这项中试研究几乎不需要任何发展时间。此外，许多构造强迫函数随弧长而变化，从而可以评估与地球化学参数的关系。这项研究的目的是确定弧中Cl同位素组成是否有足够的变化，以作为有用的岩石成因工具。更广泛的影响。这项工作将测试在俯冲带环境下使用Cl同位素示踪流体的实用性。它将利用分类良好的中美洲弧，那里的样品已经到手，可以直接与其他现有的地球化学数据（例如，氮和碳同位素组成，He/Ar）进行比较。如果成功，它将广泛适用于其他电弧系统。这项工作将成为J. Barnes获得博士后奖学金的基础，使她能够将她的地球化学专业知识扩展到活火山作用/构造作用。此外，一名本科生将为一篇荣誉论文承担这项工作的一部分，一名少数民族高中生将在暑期工作。

Intellectual merit. A proof-of-concept study is proposed to evaluate stable chlorine isotope abundances as a novel geochemical tracer of fluids derived in subduction zones. The PI has developed a robust analytical method for determination of delta37Cl values of different potential reservoirs - including sediments, pore waters, and serpentinites - all of which have distinct isotopic compositions. It is proposed that the Cl isotopic composition of fluids involved in arc magmatism should be faithfully recorded in either in volcanic gases (e.g., fumaroles) or glasses and ash. Contamination by surficial waters would have the effect of driving samples toward a near-zero delta37Cl value. The fact that preliminary data on fumarolic gases cover a range in excess of 10 permil demonstrates that this effect is minimal. Cl isotope systematics will be determined for already well characterized fumarolic gases, volcanic glasses and volcanic ash samples from the Central American volcanic arc, which is one of the MARGINS focal sites. All samples are in hand, the technique has been perfected and the postdoctoral student for whom funds are requested is an expert in the field of chlorine isotope geochemistry, thus almost no developmental time is required to carry out this pilot study. In addition, numerous tectonic forcing functions vary over the arc length - allowing relations to geochemical parameters to be evaluated. This study aims to determine whether or not there is sufficient variation in Cl isotopic composition in arcs to serve as a useful petrogenetic tool. Broader impacts. This work will test the utility of using Cl isotopes for tracing fluids in subduction zone settings. It will take advantage of the well classified Central American arc, where samples are already in hand, and can be compared directly with other existing geochemical data (e.g., N and C isotopic composition, He/Ar). If successful, it should have wide applicability to other arc systems. The work will form the basis for a postdoctoral fellowship for J. Barnes, allowing her to expand her geochemical expertise into active volcanism/tectonism. In addition, an undergraduate student will undertake a subset of this work for an honors thesis and a minority high school student will be employed for the summer.