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

知识价值：在海底伸展脊轴和岛屿喷发的海洋玄武岩的地球化学差异反映了地幔内部的一级非均质性。这种非均质性是由主要的地球过程造成的，如海洋岩石圈在俯冲带的地幔中再循环，大陆岩石圈通过剥离或大陆分裂过程和熔融/岩石反应（通常称为交代作用）再循环。这种非均质性的长期保存限制了地幔中发生的物理过程，如对流、搅拌和混合。特别重要的证据是，一个循环系统的不同部分，如海洋沉积物、上下海洋地壳、下大陆地壳，在有限的时间间隔内优先在特定的火山上取样。火山活动形成了长期存在的、随年龄发展的火锅式轨迹，比如夏威夷山脊，为我们提供了形成和维持这种非均质性的过程的直接见解。本提案的重点是定义和理解最近夏威夷火山喷发的熔岩的地球化学异质性的起源。研究夏威夷熔岩的基本原理是，夏威夷熔岩的地球化学数据可以在广泛的地球物理、地质和时间限制框架内进行解释，这些框架基于实地研究，包括陆上、海底和深钻工作。其他热点轨道缺乏这样的补充信息。研究的重点是确定(a)不相容元素丰度和放射性成因同位素比值的差异，以区分夏威夷火山的雁列Kea和Loa趋势，以及(b)这些地球化学参数随着单个火山的演化而变化。虽然像莫纳克亚山这样的克亚亚趋势火山已经得到了很好的研究，但对于经历了几个火山阶段的洛亚趋势火山，却没有类似的数据。将获得Mahukona、West Molokai和Penguin Bank（均为Loa趋势火山）火山岩的高精度地球化学数据，以确定年龄递进的地球化学趋势。这些数据将用于评估最近提出的源非均质性空间分布模型，即同心径向分区或双边不对称分区。这些备选方案对产生地球化学非均质性的物理过程有着非常不同的含义。更广泛的影响：就地球化学家的教育和培训而言，主要的影响是弗雷指导了两名博士研究生。研究工作包括国家（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，因为他们可以与更大的一群有不同想法的科学家互动，他们可以使用麻省理工学院没有的分析设备。研究结果和解释将主要由学生在国家和国际会议上发表，并在国际期刊上发表研究论文。

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.