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.

爆发的熔岩的地球化学研究，尤其是在地壳最薄的海洋盆地发现的熔岩，有助于我们了解控制地球上层地幔的组成和动态的过程，这是大多数岩浆和火山来源的来源。 了解海底熔岩喷发的基本步骤，这主要是玄武岩的组成，其地幔来源的性质是建立这些岩石中挥发物的预算和分配。这是因为分别挥发性元素和化合物，例如碳，氢，氟，氯，硫和H2O和CO2，都会影响地幔熔化，岩浆结晶以及火山喷发的位置，强度和组成。海底爆发的熔岩的丰度和挥发性组成及其空间分布在地幔流量和温度模型，在俯冲过程中脱水到地幔过程中，在岩石圈化学症上，在岩石圈化学的脱水中，在地幔中脱水，在岩石圈化学的岩石层脱水方面，在岩石圈化学质量上脱水，并在地面上的元素上，以及地球上的元素之间的元素。沿东南太平洋智利山脊爆发的熔岩独一无二，因为它们显示出弧光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异常熔岩的化学性质，并提供了其组成的全面表征，包括主要和痕量元素地球化学，它们的挥发性元素和化合物的货物以及它们的延髓，新近偏，hafnium，hafnium和铅的放射性同位素的比率。 这些数据将用于揭示有助于智利山脊岩浆的产生和演变的不同储层和过程的作用，并为地幔流量和温度模型提供了重要的限制。此外，挥发物是地球大气和海洋的关键组成部分，因此，这些数据也可以用来在地球内部和表面之间建立挥发物的循环，从而从根本上影响我们的星球的可居住性。 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，在EPSCOR州的机构的支持（即，一个未获得大量联邦款项的州）以及使本科生参与完整的研究经验，包括接受最先进的地球化学分析技术的培训。与布朗大学计划的合作，其任务是增加代表性不足的科学和技术领域的少数群体学生的数量，将努力参与研究中少数群体的本科生。与该项目有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代表三个国家的五个机构的地球化学主义者合作：美国，德国和日本。它还支持罗得岛州布朗大学的NSF资助的分析设施和马萨诸塞州的伍兹霍尔海洋学机构，并为科学少数人数不足的少数群体提供了一名调查员。东南太平洋的智利山脊的平板窗户的熔岩来自一个地区，其特征是一套独特的地质和地球化学特征：（1）它没有地球物理证据表明，由于其位置远离任何已知的太平洋海洋盆地热点，它会影响其位置，从而影响山脊； （2）这是世界上为数不多的山脊轴线俯冲的地方之一，导致南美洲大陆下方的平板窗户的发展； （3）这是世界上少数几个中山脊玄武岩具有地球化学特征更常见与弧岩浆作用相关的例子之一。这项研究提供了对这些独特的智利岭玄武岩的全面地球化学研究，为研究俯冲和中山山脊扩散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成分。这项研究将通过分析其主要，痕量和挥发性元素的内容，这些岩石的Sr，ND，PB和HF的放射性同位素比以及挥发性元件和化合物的组成和分布（C，H，H，F，F，S，S，Cl，H2O和CO2）。分析将使用布朗大学的电感耦合等离子体质谱法进行。挥发性工作将通过海洋学森林孔机构的二级离子质谱法进行，以分析代表目标智利山脊熔岩的最终成员玄武岩组成的样品中橄榄石托管的融合体的组成。新的地球化学数据将用于阐明造成东南太平洋上层壁架不同末端成员组件的产生和演变的过程。