Collaborative Research: Halogen Behavior In the Pluton-to-Volcanic Arc System

卤素元素（氟、氯、溴和碘）在大气、海洋和岩石圈中含量丰富，是高活性元素。地壳中的卤素可以影响岩浆的性质，并携带元素形成经济矿床。在火山弧系统中，卤素元素通过俯冲的地壳被带到深处，并可以在熔体中穿过覆盖的地壳，从火山喷发出来。对俯冲带输入的卤素和通过火山气体输出的卤素的估计表明，有一部分卤素被困在地球深处。卤素可能存在多种储集层，但由于难以接近和取样，这些储集层尚未得到很好的表征。一个例子是火山下的岩浆系统，其中地下岩浆房和喷发的火山岩中的卤素浓度并不为人所知。这个小组将测量侵入性深成岩和喷出性火山岩中的全部卤素，这些岩石来自现在暴露在加州内华达山脉的同一个古老弧系。这将使他们能够解决关键的开放性问题，包括：卤素是否富集于深部岩浆房或喷发的火山岩中；卤素存在于岩石中；以及卤素对岩浆过程和火山弧矿床的影响。通过这项研究，主要研究人员和研究生将设计一个具有可及性、公平性和包容性原则的矿物学和岩石学本科课程，并让本科生参与研究和安全、包容性的实地体验。本研究使用的样本子集来自一个历史收藏品。这些样本将使用3D技术进行数字化，并创建为虚拟显微镜公共网站上的教育资源。由于缺乏来自关键储层的数据，即弧前、深俯冲的板块残余物、次大陆地幔和大陆地壳的数据，地球深部的卤素运动和储层具有高度的不确定性。考虑到地幔中的卤素不相容和对更进化的熔体的亲和力，大陆地壳是一个潜在的重要储集层；然而，对深成岩和火山弧岩的大块岩石组成的研究却屈指可数。本研究将通过分析一套空间相关的深成岩和火山岩，描述弧岩浆系统中全卤素（Fl, Cl, Br， I）的组成和行为，这些岩石具有相似的化学成分和年龄。具体来说，该团队将在一套地球化学特征良好的样品上测量大块岩石卤素（Cl， F, Br， I）浓度，原位矿物浓度（F, Cl）以及O和h同位素。该样品套件将用于1)确定卤素是否集中在单一弧系统内的深部或火山剖面中，2)确定卤素的寄存位置（即矿物或其他地点），以及3)评估卤素在大陆地壳形成过程中的岩浆过程中的作用。为了解释同化和热液蚀变等过程对卤素行为的作用，他们还建议分析一个互补套件，包括下地壳捕虏体、寄主围岩（如片岩、大理岩）、热液蚀变岩和伴生岩脉，以及更多的基性岩性（如辉长岩），以加强我们的解释。该数据集将有助于了解大陆弧地壳大块岩石的卤素组成，并将其与主元素、微量元素和同位素组成一起用于评估原始岩浆过程（如地壳同化、分馏结晶）对卤素记录的影响，并通过弧岩浆系统解释整体卤素系统。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Halogen elements (fluorine, chlorine, bromine, and iodine) are abundant, highly reactive elements in the atmosphere, oceans, and lithosphere. Halogens within Earth’s crust can affect magmatic properties and carry elements to form economic mineral deposits. Within volcanic arc systems, halogen elements are carried to depth by subducting crust and can travel within melts through the overriding crust and out at volcanoes. Estimates of halogen inputs at subduction zones and outputs through volcanic gases show a deficit that suggest a portion of halogens are trapped deep within the Earth. There are multiple possible reservoirs to host halogens that are not well characterized because they are too difficult to access and sample. One example is the magmatic system under volcanoes where concentrations of halogens in subsurface magma chambers and erupted volcanic rocks are not well known. This team will measure the full halogen suite in intrusive plutonic rocks and extrusive volcanic rocks from the same ancient arc system now exposed in the Sierra Nevada, California. This will allow them to address key open questions including: whether halogens are enriched in the plutonic magma chamber or erupted volcanic rock; where halogens are hosted within the rocks; and what impact halogens have on magmatic processes and mineral deposits at volcanic arcs. Through this research, the principal investigators and graduate students will design an undergraduate mineralogy and petrology class with accessibility, equity, and inclusion principles and engage in undergraduate students in research and safe, inclusive field experiences. A subset of the samples used for this study come from an historic collection. These samples will be digitized using 3D technology and created into an educational resource hosted on the Virtual Microscope public website.Halogen movement and reservoirs within the deep Earth are highly uncertain due to the lack of data from key reservoirs, namely, the fore-arc, deeply subducted slab residues, subcontinental mantle, and – the focus of this study – continental crust. Given halogen incompatibility in the mantle and affinity towards more evolved melts, continental crust is a potentially important reservoir; however, bulk rock compositions of plutonic and volcanic arc rocks are relegated to a handful of studies. This research will characterize the full halogen (Fl, Cl, Br, I) composition and behavior within an arc magmatic system by analyzing a suite of spatially-related plutonic and volcanic rocks that share similar chemical composition and age from the Sierra Nevada Arc. Specifically, this team will measure bulk rock halogen (Cl, F, Br, I) concentrations, in-situ mineral concentrations (F, Cl), and O and H-isotopes on a suite of geochemically well-characterized samples. This sample suite will be used to 1) determine whether halogens are concentrated in the plutonic or volcanic section within a single arc system, 2) identify where halogens are hosted (i.e., in minerals or other sites), and 3) assess the role of halogens in magmatic processes during the formation of continental crust. In order to interpret the role of processes, such as assimilation and hydrothermal alteration, on halogen behavior, they also propose to analyze a complimentary suite that includes lower crustal xenoliths, host wall rocks (e.g., schists, marbles), hydrothermally altered rocks and associated veins, and more mafic lithologies (e.g., gabbros) to strengthen our interpretations. The dataset will significantly contribute to what is known of bulk rock halogen compositions for continental arc crust, and be used with major element, trace element, and isotopic compositions to evaluate the impact of primary magmatic processes (e.g., crustal assimilation, fractional crystallization) on the halogen record and interpret overall halogen systematics through the arc magmatic system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.