Collaborative Research: Constraining Arc Processes through Comprehensive Geochemical Study of the Chilean Southern Volcanic Zone

汇聚边缘的火山作用是固体地球循环的最明显和最重要的表现之一，对于我们理解地球过程以及火山喷发和地震活动对人类的危害都具有重要意义。理解这些过程需要综合的数据集，这些数据集利用了最重要的地球化学工具，这些工具是在地球提供的“自然实验”的背景下收集的。分析地球化学的新发展以及与智利火山学家的合作为这项研究提供了独特的机会。智利的“南部火山带”提供了一个实验，以了解大陆地壳如何影响火山行为和火山产物。地壳的厚度和年龄从南到北逐渐变化，这使得两种相互竞争的假说能够得到严格的评估。第一种假设认为，火山作用的变化是由于地壳对下面地幔中的熔融过程的影响，喷发的熔岩可以根据在深处发生的产生汇聚边缘火山的过程来解释。第二种观点认为，地壳将岩浆改造得面目全非，因此它们的成分反映了浅层的地壳过程，而不是更深的地幔过程。智利南部提供的对沿坡度的火山的全面研究将允许对这些假设进行详细测试，并对控制汇聚岩浆成分的因素有一个新的理解。将用于解决这一问题的工具包括智利同事提供的必要的野外工作和地质理解、常量元素、微量元素和长寿命放射性同位素的标准工具。新的观点来自于这一经典方法与氧同位素、U系列研究和宇宙成因核素10Be的结合。氧同位素对地壳污染特别敏感；U系列和10Be反映地幔过程。观察这些示踪剂的共变性将限制地壳和地幔的贡献。这项工作将回答有关固体地球循环的基本问题，这些问题与我们对板块构造旋回的总体理解有关。它还整合了美国、瑞士、法国和智利调查人员的努力。其中一些火山具有重要的历史喷发活动，这项工作将有助于未来的危险性评估。本科生、研究生和博士后都在接受火山学、管理实地考察的后勤和先进的化学分析工具方面的培训。

Volcanism at convergent margins is one of the most visible and important manifestations of the circulation of the solid Earth, with importance both for our understanding of Earth processes, and for hazards to human beings from eruptions and seismicity. Understanding these processes requires comprehensive data sets that make use of the most important geochemical tools, collected in the context of a "natural experiment" provided by the Earth. New developments in analytical geochemistry and collaboration with Chilean volcanologists provide a unique opportunity for such a study. The Chilean "southern volcanic zone" provides an experiment to see how the continental crust influences volcanic behavior and products. The thickness and age of the crust change progressively from south to north, permitting two competing hypotheses to be rigorously evaluated. The first hypothesis proposes that changes in volcanism result from the influence of the crust on melting processes in the mantle below, and that erupted melts can be interpreted in terms of the processes that take place at depth to create convergent margin volcanoes. The second argues that the crust modifies magmas beyond recognition, so that their compositions reflect shallow crustal processes rather than deeper mantle processes. A comprehensive study of volcanoes along the gradient provided by southern Chile will permit a detailed test of these hypotheses, and a new understanding of what controls convergent magma compositions. The tools that will be used to solve this problem include the necessary field work and geological understanding provided by Chilean colleagues, standard tools of major elements, trace elements, and long-lived radiogenic isotopes. The new perspectives come from the combination of this classical approach with oxygen isotopes, U-series studies, and the cosmogenic nuclide 10Be. Oxygen isotopes are particularly sensitive to crustal contamination; U-series and 10Be reflect mantle processes. Seeing how these tracers co-vary will constrain the crust and mantle contributions. This work will answer fundamental questions about solid Earth circulation that relate to our overall understanding to the plate tectonic cycle. It also integrates efforts of US, Swiss, French and Chilean investigators. Some of the volcanoes have had important historical eruptive activity, and this work will be useful to future hazard evaluation. Undergraduates, graduate students and post-docs are all receiving training in volcanology, the logistics of managing field expeditions, and advanced tools of chemical analysis.