Defining and Understanding Geochemical Heterogeneity in the Hawaiian Plume: Spatial and Temporal Geochemical Variations in Loa-trend Volcanoes

定义和理解夏威夷羽流中的地球化学异质性：洛阿趋势火山的时空地球化学变化

• 批准号: 0607895
• 负责人: Frederick Frey
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0607895&HistoricalAwards=false
• 关键词: Defining; Understanding; Geochemical; Heterogeneity; Hawaiian

Intellectual Merit: The geochemical differences between oceanic basalt erupted at submarine spreading ridge axes and islands reflect first order heterogeneity within the Earth's mantle. This heterogeneity results from major earth processes such as recycling of oceanic lithosphere into the mantle at subduction zones, recycling of continental lithosphere via delamination or continental breakup processes and melt/rock reactions, commonly described as metasomatism. The longterm preservation of such heterogeneity provides constraints on physical processes occurring in the mantle, such as convection, stirring and mixing. Especially important is evidence that different parts of a recycled system, such as oceanic sediments, upper and lower oceanic crust, lower continental crust are preferentially sampled at specific volcanoes for limited time intervals. Volcanism forming long-lived, age-progressive hotpot tracks, such as the Hawaiian Ridge, provides direct insight into the processes that form and maintain such heterogeneities. This proposal focuses on defining and understanding the origin of geochemical heterogeneity in lavas erupted at recent Hawaiian volcanoes. The rationale for studying Hawaii is that geochemical data for Hawaiian lavas can be interpreted within the context of an extensive framework of geophysical, geological and temporal constraints based on field studies including subaerial, submarine and deep drilling efforts. Such complementary information is lacking for other hotspot tracks. The research focus is on determining (a) the differences in incompatible element abundance and radiogenic isotope ratios that distinguish lavas forming the en echelon Kea and Loa trends of Hawaiian volcanoes, and (b) the variation of these geochemical parameters as an individual volcano evolves over time. Although Kea trend volcanoes, such as Mauna Kea, are well studied, similar data are not available for Loa trend volcanoes that have progressed through several volcanic stages. High precision geochemical data for lavas from Mahukona, West Molokai and Penguin Bank (all Loa trend volcanoes) will be obtained to define age-progressive geochemical trends. These data will be used to evaluate recently proposed models for the spatial arrangement of source heterogeneities, i.e. concentric radial zonation or bilateral asymmetric zonation. These alternatives carry very different implications for the physical processes that create geochemical heterogeneities.Broader Impacts: In terms of education and training as geochemists, the major impact is mentoring by Frey of two PhD graduate students. The research effort includes national (Woods Hole Oceanographic Institution and Monterey Bay Aquarium Research Institute) and international collaborations (Max-Planck-Institut fur Chemie and Ecole Normale Superieure de Lyon, France). These interactions expand the student horizons in that they interact with a larger group of scientists with diverse ideas, and they have access to analytical facilities not available at MIT. The research results and interpretations will be disseminated by presentations, dominantly by students, at national and international meetings and publications of research papers in international journals.

智力优点：海底扩张脊轴和岛屿喷发的海洋玄武岩之间的地球化学差异反映了地幔内的一级异质性。这种异质性是由主要的地球过程造成的，例如海洋岩石圈在俯冲带再循环到地幔中，大陆岩石圈通过分层或大陆裂解过程和熔体/岩石反应（通常称为交代作用）再循环。这种异质性的长期保存限制了地幔中发生的物理过程，例如对流、搅拌和混合。尤其重要的是，有证据表明，循环系统的不同部分，例如海洋沉积物、上洋地壳和下洋地壳、下大陆地壳，优先在有限的时间间隔内在特定火山进行采样。火山作用形成了长期存在、年龄渐进的火锅轨迹，例如夏威夷山脊，为了解形成和维持这种异质性的过程提供了直接的见解。该提案的重点是定义和理解最近夏威夷火山喷发的熔岩中地球化学异质性的起源。研究夏威夷的基本原理是，夏威夷熔岩的地球化学数据可以在基于地面、海底和深钻探工作等实地研究的地球物理、地质和时间限制的广泛框架内进行解释。其他热点轨道缺乏此类补充信息。研究重点是确定 (a) 不相容元素丰度和放射性同位素比率的差异，这些差异可区分形成夏威夷火山凯亚火山和洛阿火山趋势的熔岩，以及 (b) 随着单个火山的演化，这些地球化学参数的变化时间。尽管对莫纳克亚火山等凯阿趋势火山进行了深入研究，但对于经历了几个火山阶段的洛阿趋势火山，还没有类似的数据。将获得马胡科纳、西摩洛凯岛和企鹅滩（所有洛阿趋势火山）熔岩的高精度地球化学数据，以确定年龄渐进的地球化学趋势。这些数据将用于评估最近提出的源异质性空间排列模型，即同心径向分区或双边不对称分区。这些替代方案对造成地球化学异质性的物理过程具有截然不同的影响。更广泛的影响：在地球化学家的教育和培训方面，主要影响是弗雷对两名博士研究生的指导。研究工作包括国家合作（伍兹霍尔海洋研究所和蒙特利湾水族馆研究所）和国际合作（马克斯普朗克化学研究所和法国里昂高等师范学院）。这些互动扩大了学生的视野，因为他们与更多具有不同想法的科学家进行互动，并且他们可以使用麻省理工学院没有的分析设施。研究结果和解释将通过在国内和国际会议上的演讲（主要由学生）以及在国际期刊上发表研究论文的方式传播。