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

卤素元素(氟、氯、溴和碘)是大气、海洋和岩石圈中丰富的、高活性的元素。地壳中的卤素可以影响岩浆性质，并携带形成经济矿藏的元素。在火山弧系统中，卤素元素被俯冲的地壳带到深处，并可以在熔体中通过覆盖地壳运往火山。对俯冲带的卤素输入和火山气体输出的估计显示，存在赤字，这表明部分卤素被困在地球深处。有多种可能的水库含有卤素，但由于太难获取和采样，因此没有很好地描述这些卤素。一个例子是火山下的岩浆系统，地下岩浆室和喷发的火山岩中卤素的浓度并不为人所知。这个团队将在侵入的深成岩和喷出的火山岩中测量完整的卤素套件，这些岩石来自现已暴露在加利福尼亚州内华达山脉的同一古老弧系。这将使他们能够解决关键的悬而未决的问题，包括：深成岩浆室或喷发的火山岩中是否富含卤素；卤素在岩石中的宿主位置；以及卤素对火山弧的岩浆过程和矿物沉积有什么影响。通过这项研究，主要研究人员和研究生将设计一门具有可及性、公平性和包容性原则的本科生矿物学和岩石学课程，并让本科生参与研究和安全、包容的野外体验。这项研究使用的样本的一个子集来自历史收藏。这些样品将使用3D技术数字化，并制作成虚拟显微镜公共网站上的教育资源。由于缺乏来自关键储集层的数据，地球深处的卤素运动和储集层高度不确定，这些储集层是弧前、深俯冲板块残留物、次大陆地幔，以及--本研究的重点--大陆地壳。考虑到地幔中的卤素不相容和对更演化的熔体的亲和力，大陆地壳是一个潜在的重要储集层；然而，深成岩和火山弧岩的大部分岩石成分仅限于少数几个研究。这项研究将通过分析内华达山脉弧区具有相似化学成分和年龄的一套空间相关的深成岩和火山岩，来表征弧状岩浆系统中的全卤素(Fl，Cl，Br1，I)的组成和行为。具体地说，该团队将测量大量岩石的卤素(氯、氟、溴、碘)浓度、原位矿物浓度(氟、氯)以及氧和氢同位素。这套样品将用于1)确定卤素是否集中在单个弧系内的深成岩段或火山岩部分，2)确定卤素赋存的地方(即，在矿物或其他地点)，以及3)评估卤素在大陆地壳形成期间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，他们还建议分析包括下地壳捕虏体、寄主围岩(例如片岩、大理岩)、热液蚀变岩石和伴生脉体以及更多镁铁质岩性(例如辉长岩)的补充套，以加强我们的解释。该数据集将对大陆弧壳的块状岩石卤素组成的已知做出重大贡献，并与主要元素、微量元素和同位素组成一起用于评估原始岩浆过程(例如，地壳同化、分离结晶)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NSF的法定使命，并通过使用基金会的智力优势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.