The Volatile Contents of the Chile Ridge Mid-Ocean Ridge Basalts, Unraveling their Arc Signature

对喷发熔岩的地球化学研究，特别是在地壳最薄的海洋盆地中发现的熔岩，有助于我们了解控制地球上地幔成分和动力学的过程，而地球上地幔是大多数岩浆和火山的来源。了解海底熔岩的喷发及其地幔源的性质的一个基本步骤是建立这些岩石中挥发物的预算和分布。海底熔岩的成分主要是玄武岩。这是因为挥发性元素和化合物，如碳、氢、氟、氯、硫、水和二氧化碳，分别影响地幔熔化、岩浆结晶以及火山喷发的位置、强度和组成。海底喷发熔岩的丰度、挥发性成分及其空间分布对地幔流动和温度模式、俯冲过程中俯冲到地幔中的海洋岩石圈脱水、岩石圈交代作用以及地表和深部储层之间元素循环提供了重要的约束。东南太平洋智利海脊喷发出的熔岩具有弧熔岩的地球化学特征，而不是海底玄武岩，这是其独特之处。本研究考察了这些不寻常熔岩的化学成分，并提供了其组成的综合特征，包括主要和微量元素的地球化学特征，挥发性元素和化合物的货物，以及锶、钕、铪和铅的放射性同位素的比例。这些数据将用于揭示不同储层的作用以及对智利海脊岩浆活动的产生和演化有贡献的过程，并为地幔流动和温度模型提供重要的约束。此外，挥发物是地球大气和海洋的关键成分，因此，这些数据也可以用来建立地球内部和表面之间的挥发物循环，这从根本上影响了我们星球的可居住性。这项工作的更广泛影响包括支持早期职业研究科学家，支持EPSCoR州（即不接受大量联邦资金的州）的机构，并让本科生参与完整的研究经验，包括最先进的地球化学分析技术培训。与布朗大学（Brown University）旨在增加科学和技术领域少数族裔学生人数的项目合作，将努力让少数族裔本科生参与研究。与该项目相关的公共宣传将通过布朗大学科学中心宣传和公共事务办公室进行。这项工作还促进了与代表美国、德国和日本三个国家的五个机构的地球化学家的合作。它还支持美国国家科学基金会资助的罗德岛布朗大学和马萨诸塞州伍兹霍尔海洋研究所的分析设施，并资助一名来自科学领域代表性不足的少数群体的研究人员。来自东南太平洋智利海脊板块窗的熔岩来自一个具有独特地质和地球化学特征的地区：(1)由于其位置远离任何已知的太平洋盆地热点，没有地幔柱影响海脊的地球物理证据；(2)它是世界上为数不多的已知位置之一，目前脊轴正在俯冲，导致南美洲大陆下的板窗发育；(3)洋中脊玄武岩具有地球化学特征，是世界上为数不多的与弧岩浆活动有关的例子之一。本研究对智利海脊玄武岩进行了全面的地球化学研究，为研究俯冲和洋中脊扩张过程之间的相互作用提供了独特的机会。这些独特的火山岩起源的重要线索是它们的挥发性含量及其组成。本研究将通过分析原始海底玻璃的主要元素、微量元素和挥发性元素含量，分析岩石中Sr、Nd、Pb和Hf的放射性成因同位素比值，以及挥发性元素和化合物（C、H、F、S、Cl、H2O和CO2）的组成和分布，全面表征原始海底玻璃。分析将在布朗大学使用电感耦合等离子体质谱法进行。挥发性工作将在伍兹霍尔海洋研究所通过二次离子质谱法进行，以分析样品中含有橄榄石的熔融包裹体的组成，这些包裹体代表了目标智利岭熔岩的端元玄武岩成分。新的地球化学数据将用于揭示形成东南太平洋上地幔的不同端元组分的产生和演化过程。

Geochemical studies of erupted lavas, especially those found in ocean basins, where Earth's crust is thinnest, helps us to understand processes that control the composition and dynamics of the Earth's upper mantle, which is the source from which most magmas and volcanos come. A fundamental step in understanding the eruption of seafloor lavas, which are mostly basaltic in composition, and the nature of their mantle source is to establish the budget and distribution of volatiles in these rocks. This is because volatile elements and compounds, like Carbon, Hydrogen, Fluorine, Chlorine, Sulfur, and H2O and CO2, respectively, influence mantle melting, magma crystallization, and the location, strength, and composition of volcanic eruptions. The abundance and volatile composition of seafloor-erupted lavas and their spatial distribution provide important constraints on models of mantle flow and temperature, on the dehydration of oceanic lithosphere subducted into the mantle during the subduction process, on lithospheric metasomatism, and on the cycling of elements between Earth's surface and deep reservoirs. The lavas erupted along the Chile Ridge in the southeast Pacific Ocean are unique in that they show geochemical characteristics of arc lavas, instead of seafloor basalts. This research examines the chemistry of these unusual lavas and provides a comprehensive characterization of their composition including major and trace element geochemistry, their cargo of volatile elements and compounds, and their ratios of the radiogenic isotopes of Strontium, Neodymium, Hafnium, and Lead. These data will be used to unravel the role of the different reservoirs and processes contributing to the generation and evolution of Chile Ridge magmatism as well as provide important constraints on models of mantle flow and temperature. Moreover, volatiles are key constituents of the Earth's atmosphere and oceans and, thus, these data can also be used to establish the cycles of volatiles between the Earth's interior and surface which fundamentally affects our planet's habitability. Broader impacts of the work include support of an early career research scientist, support of an institution in an EPSCoR state (i.e., a state that does not receive significant federal monies) and engaging undergraduate students in the full research experience, including training in state-of-the-art geochemical analytical techniques. Working with Brown University programs whose missions are to increase the number of under-represented minority students in science and technology fields, efforts will be made to engage undergraduates from minority groups in the research. Public outreach, related to the project, will be carried out through the Brown University Science Center Outreach and Public Affairs Office. The work also promotes the collaboration with geochemists from five institutions representing three countries: USA, Germany, and Japan. It also supports NSF-funded analytical facilities at Brown University in Rhode Island and the Woods Hole Oceanographic Institution in Massachusetts and funds an investigator from a minority group under-represented in the sciences. Lavas from the slab window on the Chile Ridge, in the southeast Pacific Ocean, come from a region characterized by a unique set of geological and geochemical characteristics: (1) it has no geophysical evidence for a mantle plume affecting the ridge due to its location away from any known Pacific Ocean Basin hotspot; (2) it is one of the few known locations in the world where the ridge axis is currently being subducted resulting in the development of a slab window under the South American continent; and (3) it is one of the few examples in the world where mid-ocean ridge basalts have geochemical characteristics more commonly associated with arc magmatism. This research provides a comprehensive geochemical study of these unique Chile Ridge basalts, providing a unique opportunity to study the interaction between subduction and mid-ocean ridge spreading processes. An important clue to the origin of these unique volcanic rocks is their volatile content and its composition. This research will fully characterize primitive submarine glasses by analyzing their major, trace, and volatile element contents, the radiogenic isotope ratios of Sr, Nd, Pb, and Hf of these rocks, and the composition and distribution of volatile elements and compounds (C, H, F, S, Cl, H2O, and CO2). Analyses will be carried out using inductively-coupled plasma mass spectrometry at Brown University. The volatile work will be done via secondary ion mass spectrometry at the Woods Hole Institution of Oceanography to analyze the composition of olivine-hosted melt inclusions in samples that represent the end-member basaltic compositions of the targeted Chile Ridge lavas. The new geochemical data will be used to unravel the processes contributing to the generation and evolution of different end-member components forming the southeast Pacific upper mantle.