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

对喷发的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的组成和动力学的过程，而上地幔是大多数岩浆和火山的来源。要了解海底熔岩的喷发及其地幔来源的性质，一个基本步骤是确定这些岩石中挥发物的平衡和分布。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，分别影响地幔熔融、岩浆结晶以及火山喷发的位置、强度和成分。海底喷发熔岩的丰度和挥发成分及其空间分布对地幔流动和温度模型、俯冲过程中俯冲到地幔中的大洋岩石圈的脱水、岩石圈交代作用以及地球表面和深层储层之间的元素循环提供了重要的制约因素。沿东南太平洋智利海脊喷发的熔岩具有独特之处，因为它们显示出弧状熔岩的地球化学特征，而不是海底玄武岩。这项研究考察了这些不同寻常的熔岩的化学成分，并提供了它们的组成的全面特征，包括主元素和微量元素地球化学，它们的挥发性元素和化合物的货物，以及它们的放射性成因的锶、钕、氦和铅同位素的比率。这些数据将被用来揭示有助于智利山脊岩浆活动形成和演化的不同储集层和过程的作用，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，这些数据还可以用来建立地球内部和表面之间的挥发物循环，这从根本上影响我们地球的宜居性。这项工作的更广泛影响包括对早期职业研究科学家的支持，对EPSCoR州(即没有获得大量联邦资金的州)的机构的支持，以及让本科生参与全面的研究体验，包括最先进的地球化学分析技术培训。与布朗大学的项目合作，这些项目的使命是增加科技领域中未被充分代表的少数族裔学生的数量，将努力吸引少数族裔群体的本科生参与研究。将通过布朗大学科学中心外联和公共事务办公室开展与该项目有关的公众外联活动。这项工作还促进了与来自代表三个国家的五个机构的地球化学家的合作：美国、德国和日本。它还资助了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，并资助了科学界代表性不足的少数群体的一名调查人员。来自东南太平洋智利海脊上板岩窗口的熔岩来自一个具有一套独特地质和地球化学特征的区域：(1)它没有地球物理证据表明地幔热柱影响到该海脊，因为它的位置远离任何已知的太平洋盆地热点；(2)它是世界上为数不多的脊轴目前被俯冲的已知地点之一，从而导致在南美洲大陆下方形成一个板岩窗口；(3)它是世界上少数几个大洋中脊玄武岩具有更常与弧岩浆作用有关的地球化学特征的例子之一。这项研究对这些独特的智利海脊玄武岩进行了全面的地球化学研究，为研究俯冲和大洋中脊扩张过程之间的相互作用提供了一个独特的机会。关于这些独特的火山岩起源的一条重要线索是它们的挥发性成分和成分。这项研究将通过分析原始海底玻璃的主、痕量和挥发性元素含量，这些岩石的锶、钕、铅、氢的放射性同位素比值，以及挥发性元素和化合物(C、H、F、S、氯、水和二氧化碳)的组成和分布，来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进行。挥发性工作将通过伍兹霍尔海洋研究所的二次离子质谱仪来完成，以分析代表目标智利山脊熔岩的终端成员玄武岩成分的样品中橄榄石承载的熔体包裹体的组成。新的地球化学数据将用于揭示有助于形成东南太平洋上地幔的不同端元成分的生成和演化的过程。

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.