SGER: Chlorine Isotopes as Tracers of Subduction Zone Fluids

智力上的优点。 提出了一个概念验证研究，以评估稳定的氯同位素丰度作为一种新的地球化学示踪剂的流体在俯冲带。PI开发了一种可靠的分析方法，用于确定不同潜在储层（包括沉积物、孔隙沃茨和蛇纹岩）的δ 37 Cl值，所有这些储层都具有不同的同位素组成。弧岩浆作用中流体的Cl同位素组成应忠实地记录在火山气体中（如，或玻璃杯和灰。 表面活性剂沃茨的污染会使样品的δ 37 Cl值接近零。关于碳氢化合物气体的初步数据涵盖了超过10 permil的范围，这一事实表明这种影响是最小的。 Cl同位素系统学将被确定为已经很好地表征了来自中美洲火山弧的火山气体、火山玻璃和火山灰样品，该火山弧是MARGINS焦点之一。所有样品都已到手，技术已经完善，申请资金的博士后是氯同位素地球化学领域的专家，因此几乎不需要开发时间来进行这项试点研究。此外，许多构造强迫函数在弧长上变化，从而可以评估与地球化学参数的关系。本研究的目的是确定是否有足够的变化，在弧氯同位素组成，作为一个有用的成岩工具。 更广泛的影响。这项工作将测试使用Cl同位素示踪俯冲带设置中的流体的效用。它将利用分类良好的中美洲弧，那里的样品已经掌握，可以直接与其他现有的地球化学数据进行比较（例如，N和C同位素组成，He/Ar）。如果成功，它应该具有广泛的适用性，以其他电弧系统。这项工作将为J.巴恩斯的博士后奖学金奠定基础，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，一名本科生将承担这项工作的一个子集的荣誉论文和少数民族高中生将被雇用的夏天。

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.