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

智利海脊大洋中脊玄武岩的挥发性成分，揭示了它们的弧特征

• 批准号: 1657659
• 负责人: Alberto Saal
• 金额: $ 21.45万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-02-15 至 2022-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657659&HistoricalAwards=false
• 关键词: Volatile; Contents; Chile; Ridge; Mid

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.

对喷发熔岩的地球化学研究，尤其是在地壳最薄的洋盆中发现的熔岩，有助于我们了解控制地球上地幔成分和动力学的过程，而上地幔是大多数岩浆和火山的来源。 了解海底熔岩的喷发（其成分主要是玄武岩）及其地幔来源的性质的一个基本步骤是确定这些岩石中挥发物的预算和分布。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、强度和成分。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元素循环提供了重要的约束地球表面和深层水库之间。东南太平洋智利海脊沿线喷发的熔岩的独特之处在于，它们表现出弧熔岩的地球化学特征，而不是海底玄武岩。这项研究检查了这些不寻常熔岩的化学成分，并对其成分进行了全面的表征，包括主量和微量元素地球化学、挥发性元素和化合物的含量，以及锶、钕、铪和铅的放射性同位素的比率。 这些数据将用于揭示不同储层和过程对智利海岭岩浆作用的产生和演化的作用，并为地幔流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，这些数据还可用于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星球的可居住性。 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（即没有收到大量联邦资金的州）机构的支持以及让本科生参与完整的研究体验，包括州培训最先进的地球化学分析技术。布朗大学的项目旨在增加科学技术领域代表性不足的少数族裔学生的数量，我们将与布朗大学项目合作，努力让少数族裔本科生参与研究。与该项目相关的公共外展将通过布朗大学科学中心外展和公共事务办公室进行。这项工作还促进了与来自美国、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州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界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，没有地球物理证据表明地幔柱影响了海脊远离任何已知的太平洋盆地热点地区； (2) 它是世界上为数不多的已知山脊轴目前正在俯冲并导致南美大陆下方形成板窗的地点之一； (3)它是世界上为数不多的洋中脊玄武岩具有与岛弧岩浆作用更常见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。 这些独特火山岩起源的重要线索是其挥发物含量及其成分。本研究将通过分析原始海底玻璃的主量、痕量、挥发性元素含量，岩石中Sr、Nd、Pb、Hf的放射性同位素比值，以及挥发性元素和化合物（C、C、 H、F、S、Cl、H2O 和 CO2）。分析将在布朗大学使用电感耦合等离子体质谱法进行。挥发性工作将通过伍兹霍尔海洋学研究所的二次离子质谱法完成，以分析代表目标智利山脊熔岩端元玄武岩成分的样品中橄榄石熔融包裹体的成分。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成分的生成和演化过程。