SGER: Chlorine Isotopes as Tracers of Subduction Zone Fluids

智力上的优点。 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。建议在火山气体（例如喷气孔）或玻璃和火山灰中忠实记录弧岩浆作用流体的 Cl 同位素组成。 地表水的污染会导致样品的 delta37Cl 值接近于零。事实上，有关富马酸气体的初步数据覆盖超过 10 permil 的范围，这一事实表明这种影响很小。 将对来自中美洲火山弧（MARGINS 焦点地点之一）的已充分表征的喷气孔气体、火山玻璃和火山灰样品确定 Cl 同位素系统学。样品已全部掌握，技术已经完善，且申请资助的博士后是氯同位素地球化学领域的专家，因此开展这项试点研究几乎不需要开发时间。此外，许多构造强迫函数随着弧长的变化而变化，从而可以评估与地球化学参数的关系。本研究旨在确定弧中 Cl 同位素组成是否存在足够的变化，以作为有用的岩石成因工具。 更广泛的影响。这项工作将测试使用 Cl 同位素在俯冲带环境中追踪流体的实用性。它将利用分类良好的中美洲弧，其中已有样品，并且可以直接与其他现有地球化学数据（例如 N 和 C 同位素组成、He/Ar）进行比较。如果成功的话，它应该对其他电弧系统具有广泛的适用性。这项工作将为 J. Barnes 的博士后奖学金奠定基础，使她能够将其地球化学专业知识扩展到活火山/构造运动领域。此外，一名本科生将承担这项工作的一部分以完成荣誉论文，一名少数族裔高中生将在暑假受雇。

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.