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

夏威夷-皇帝链是地球上最长（6000公里）、最大（600万立方公里）、最活跃（超过8000万年的100座火山）的热点省份之一。夏威夷-皇帝链广泛的火山活动是由夏威夷地幔柱引起的，它从核心-地幔边界浮力上升，产生了近代地质时代最热、最原始的玄武岩熔岩。对夏威夷-皇帝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非均质性的本质。皇帝海山是夏威夷皇帝链中最古老、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（年龄测定）研究，将解决皇帝海山的时间进展及其与夏威夷群岛相比不寻常的玄武岩成分的起源。这项研究的结果将有助于测试关于夏威夷地幔柱早期动力学及其与太平洋板块构造历史关系的有争议的模型。作为该项目的一部分，将为当地高中和社区大学学生开设一个综合暑期课程。这个暑期项目的长期目标是增加当地（特别是夏威夷原住民和太平洋岛民）大学生在STEM的数量和多样性，让他们接触到(1)地球科学领域令人兴奋的职业范围，(2)地球过程对夏威夷群岛和人民的深远影响（例如，火山爆发，地震，山体滑坡和季节性洪水）。本项目将利用皇山玄武岩的地球化学（主要元素和微量元素，以及Pb-Sr-Nd-Hf同位素比值）和地质年代学（40Ar/39Ar增量加热）研究夏威夷-皇山链最古老（~80-50 Ma）和最神秘的火山的时间组成演化。主要目标是1)描绘夏威夷地幔柱从近脊环境到远离板块边界的近期上升流的转变；2)提高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？第二古老皇帝海山（~81 ~ 76 Ma）底特律的玄武岩成分已枯竭；有些与太平洋中洋脊玄武岩（MORB）相同。底特律玄武岩的两种模型将被测试：(a)周围耗尽的太平洋上地幔被卷入夏威夷羽流，或(b)耗尽的下地幔成分（夏威夷羽流固有的）融化到异常高的程度和浅的深度。这些枯竭的地幔模型都与太平洋板块的重建相一致，这表明底特律是在靠近洋中脊轴线的年轻、薄的海洋岩石圈上形成的。(2)明治海山有多少年的历史？来自最古老的天皇海山明治的拉斑玄武岩将被用来限制太平洋盆地的一次主要构造震动，以及已知的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)帝王海山的年龄有无变化？地球动力学模型表明，夏威夷-皇帝弯曲是由夏威夷羽流快速向南运动引起的，而不是太平洋板块运动的突然变化。皇帝海山玄武岩的新年代测定将用于确定迁移速率，并为未来的地球动力学模型提供背景。(4)沿皇帝海山，贫Kea型和detroit型地幔非均质分布如何？玄武岩化学的详细时空图将有助于限制夏威夷羽流早期动力学的模型。自上而下(5)还是自下而上(6)的地球动力学模型能最好地解释这些时空组成趋势？微量元素和同位素图将用于区分底特律成分的上地幔和下地幔起源。自上而下的模型（例如，羽脊相互作用或洋中脊捕获羽流）将得到上地幔起源的支持，而自下而上的模型（例如，地幔风）将得到下地幔（即羽流）起源的支持。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知识价值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.