Collaborative Research: Early Evolution of the Hawaiian Plume from the Geochemistry and Geochronology of Basalts Spanning the Entire Emperor Seamount Chain

夏威夷-帝王链是地球上最长(6000公里)、最大(600万立方公里)、最持续活跃(100座火山超过8000万年)的热点省份之一。夏威夷-帝王链的广泛火山活动是由夏威夷地幔热柱引起的，它从核-地幔边界漂浮上升，产生了一些最近地质时代最热和最原始的玄武岩熔岩。对夏威夷-帝王链的研究导致了对地球科学至关重要的重大发现和概念，包括板块构造和深部地幔成分不均质性的性质。皇帝海山是夏威夷帝王链中最古老、研究最少、最神秘的部分。该项目是一项详细的地球化学(熔岩化学)和地质年代学(年龄确定)研究，将解决皇帝海山的时间进程及其与夏威夷群岛相比不寻常的玄武岩成分的来源。这项研究的结果将有助于对夏威夷地幔热柱早期动力学及其与太平洋板块构造历史的关系的有争议的模型进行测试。作为该项目的一部分，将启动一项针对当地高中和社区大学学生的综合暑期计划。这个暑期计划的长期目标是增加STEM当地(特别是夏威夷原住民和太平洋岛民)大学生的数量和多样性，让他们接触到(1)激动人心的地球科学职业范围和(2)地球过程对夏威夷群岛和人类产生的深刻影响(例如，火山喷发、地震、山体滑坡和季节性洪水)。该项目将利用地球化学(主要和微量元素)研究夏威夷-帝王链中最古老(~80-50 Ma)和最神秘的火山的时间成分演变。以及帝海山玄武岩的年代学(40Ar/39Ar增量加热)。主要目标是1)描绘夏威夷地幔热柱从近山脊环境向远离板块边界的最近上升流的过渡；2)增进对太平洋地幔动力学的理解。这项研究将回答六个关键问题：(1)为什么底特律海山的玄武岩如此枯竭？来自底特律的玄武岩是第二古老的帝王海山(~81-76 Ma)，成分亏损；一些与太平洋大洋中脊玄武岩(MORB)相同。底特律玄武岩的两个模型将被测试：(A)环境贫化的太平洋上地幔卷入夏威夷热柱中，或(B)夏威夷热柱固有的贫化的下地幔成分熔融到异常高和浅的深度。这些枯竭的地幔模型都与太平洋板块的重建一致，表明底特律是在靠近大洋中脊轴线的年轻而薄的大洋岩石圈上形成的。(2)明治海山的年龄是多少？来自最古老的海山天皇明治的玄武岩将被用来约束太平洋盆地的一次重大构造变动，以及底特律地幔成分枯竭对夏威夷-天皇链玄武岩组成的最早影响。(3)皇帝海山的年龄进程是否存在差异？地球动力学模型表明，夏威夷-帝王弯曲是由夏威夷羽流的快速南移造成的，而不是太平洋板块运动的突然变化。来自皇帝海山的玄武岩的新年龄将被用来确定迁移速度，并为未来的地球动力学模型提供背景。(4)皇帝海山沿线亏损的Kea型和底特律型地幔不均质性分布情况如何？一张详细的玄武岩化学时空图将有助于约束夏威夷羽流早期动力学的模型。自上而下(5)或自下而上(6)的地球动力学模型能最好地解释这些时间-空间-组成趋势吗？微量元素和同位素图谱将被用来区分底特律部分的上地幔起源和下地幔起源。自上而下的模型(例如，烟柱-海脊相互作用或被大洋中脊捕获的烟柱)将得到上地幔起源的支持，而自下而上的模型(例如，地幔风)将得到来自下地幔(即，烟柱)的支持。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Hawaiian-Emperor Chain is one of the longest (6,000 km), largest (6 million cubic km), and most persistently active (100 volcanoes over ~80 million years) hotspot provinces on Earth. The extensive volcanism of the Hawaiian-Emperor Chain is caused by the Hawaiian mantle plume, which rises buoyantly from the core-mantle boundary and produces some of the hottest and most primitive basalt lavas in recent geological time. Studies of the Hawaiian-Emperor Chain have led to major discoveries and concepts of critical importance to the Earth Sciences, including plate tectonics and the nature of compositional heterogeneity in the deep mantle. The Emperor Seamounts are the oldest, least studied, and most enigmatic portion of the Hawaiian-Emperor Chain. This project is a detailed geochemical (lava chemistry) and geochronological (age determination) study that will resolve the temporal progression of the Emperor Seamounts and the origin of their unusual basalt compositions compared to the Hawaiian Islands. The results of this study will facilitate testing of controversial models on the early dynamics of the Hawaiian mantle plume and its relationship to the history of Pacific plate tectonics. An integrated summer program for local high school and community college students will be initiated as part of this project. The long-term goal of this summer program is to increase the number and diversity of local (especially Native Hawaiian and Pacific Islander) college students in STEM by exposing them to the (1) exciting range of careers in the Geosciences and (2) the profound impact that Earth processes have on the Hawaiian Islands and people (e.g., volcanic eruptions, earthquakes, landslides, and seasonal flooding).This project will examine the temporal-compositional evolution of the oldest (~80-50 Ma) and most enigmatic volcanoes of the Hawaiian-Emperor Chain using the geochemistry (major and trace elements, and Pb-Sr-Nd-Hf isotope ratios) and geochronology (40Ar/39Ar incremental heating) of Emperor Seamount basalts. The major goals are 1) to delineate the transition of the Hawaiian mantle plume from a near-ridge environment to the recent style of upwelling that is far from plate boundaries and 2) improve understanding of Pacific mantle dynamics. The research will answer six key questions: (1) Why are basalts from Detroit Seamount so depleted? Basalts from Detroit, the second oldest Emperor Seamount (~81-76 Ma), are compositionally depleted; some are identical to Pacific mid-ocean ridge basalts (MORB). Two models for Detroit basalts will be tested: (a) entrainment of the ambient depleted Pacific upper mantle into the Hawaiian plume or (b) melting of a depleted lower mantle component—intrinsic to the Hawaiian plume—to an unusually high degree and shallow depth. These depleted mantle models are each consistent with Pacific plate reconstructions that suggest Detroit formed on young, thin oceanic lithosphere near the axis of a mid-ocean ridge. (2) How old is Meiji Seamount? Tholeiitic basalts from Meiji, the oldest Emperor Seamount, will be used to constrain a major tectonic shakeup in the Pacific basin and the earliest known influence of the depleted Detroit mantle component on the composition of Hawaiian-Emperor Chain basalts. (3) Has the age progression of the Emperor Seamounts varied? Geodynamic models suggest that the Hawaiian-Emperor bend was caused by the rapid southward motion of the Hawaiian plume rather than an abrupt change in Pacific plate motion. New dating of basalts from the Emperor Seamounts will be used to nail down the migration rate and provide context for future geodynamic models. (4) What is the distribution of the depleted Kea- and Detroit-types of mantle heterogeneities along the Emperor Seamounts? A detailed temporal-spatial map of basalt chemistry will help to constrain models for the early dynamics of the Hawaiian plume. Does a top-down (5) or bottom-up (6) geodynamic model best explain these temporal-spatial-compositional trends? The trace element and isotopic map will be used to distinguish an upper vs. lower mantle origin for the Detroit component. A top-down model (e.g., plume-ridge interaction or plume capture by a mid-ocean ridge) would be supported by an upper mantle origin, whereas a bottom-up model (e.g., mantle wind) would be supported by a lower mantle (i.e., plume) origin.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.