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

智力优势：海底扩张脊轴和岛屿上爆发的大洋玄武岩的地球化学差异反映了地幔内部的一级不均匀性。这种不均匀性的结果，从主要的地球过程，如海洋岩石圈再循环到地幔在俯冲带，大陆岩石圈的再循环通过拆沉或大陆解体过程和熔体/岩石反应，通常被描述为交代作用。这种不均匀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。特别重要的是，有证据表明，一个再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，在特定的火山上，在有限的时间间隔内优先取样。火山作用形成了长寿的、年龄渐进的热锅轨迹，如夏威夷山脊，为形成和维持这种非均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不均匀性的起源。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种补充信息。研究的重点是确定（a）不相容元素丰度和放射性同位素比值的差异，区分熔岩形成的夏威夷火山的雁列Kea和Loa趋势，和（B）这些地球化学参数的变化，作为一个单独的火山演化随着时间的推移。虽然Kea趋势火山，如Mauna Kea，已经得到了很好的研究，但对于经历了几个火山阶段的Loa趋势火山，还没有类似的数据。将获得Mahukona、West Molokai和Penguin Bank（所有Loa趋势火山）熔岩的高精度地球化学数据，以确定年龄递进地球化学趋势。这些数据将被用来评估最近提出的模型的源的非均匀性，即同心放射状分带或双边不对称分带的空间布局。这些替代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影响。更广泛的影响：在地球化学家的教育和培训方面，主要的影响是弗雷对两名博士研究生的指导。研究工作包括国家（伍兹霍尔海洋研究所和蒙特雷湾水族馆研究所）和国际合作（马克斯-普朗克化学研究所和法国里昂师范学院）。这些互动扩大了学生的视野，因为他们与一个更大的科学家群体与不同的想法，他们有机会获得在麻省理工学院没有的分析设施。研究结果和解释将通过主要由学生在国家和国际会议上发表演讲以及在国际期刊上发表研究论文来传播。

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.