Spatiotemporal Variability of Tungsten-182 in the Hawaiian Plume

夏威夷羽流中钨 182 的时空变化

• 批准号: 2121979
• 负责人: Richard Walker
• 金额: $ 38.37万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2121979&HistoricalAwards=false
• 关键词: Spatiotemporal; Variability; Tungsten; 182; Hawaiian

The isotopic composition of the element tungsten is important to measure in some types of volcanic rocks because differences in the abundance of the isotope of tungsten-182 occurred very early in the history of the Earth due to the radioactive decay of an isotope of another element, hafnium-182. Hafnium-182 was present in our solar system for only about the first 70 million years of its history. This means that some of the magmas that crystallize to form volcanic rocks came from places within the Earth’s mantle that formed more than 4 billion years ago and that did not mix with other mantle rocks. For this study the isotopic composition of tungsten will be measured in rocks from the Hawaiian Islands. Studies have shown that the isotopic composition of tungsten in rocks from volcanic oceanic islands like the Hawaiian Islands varies. Tungsten isotopic variations that will be measured by this study will provide important new information about how the Earth formed and separated into a metal core, and silicate mantle and crust. The information will also provide hints about where these old parts of the mantle may be and how they end up in volcanic rocks. The results will give scientists who model the movement of rocks and melts in the mantle new insights about how the Earth currently cools itself from the inside out. This project will support a Ph.D. student and a postdoctoral Research Associate to conduct most of the, and will also involve contributions from an undergraduate student as part of a senior thesis project. High-precision isotopic analysis will be conducted on tungsten extracted from a suite of carefully chosen Hawaiian lavas that, based on long-lived radiogenic isotope systems and trace element abundances. The University of Maryland laboratory has been a world leader in tungsten isotope research of this type over the past decade. The various geochemical signals have previously been interpreted to sample various recycled and deep mantle components. Prior work on ocean island basalts, as well as other types of rocks (young and old), has demonstrated the laboratory’s capability to cleanly separate tungsten from rocks, and generate highly-precise isotopic measurements using thermal ionization mass spectrometry. The primary objective of this study will be to identify and interpret small tungsten isotopic “anomalies” and attempt to relate the anomalies to other geochemical tracers, such as Nd, Pb and Os isotopic composition, potentially allowing connections to be made between the timing and nature of both early Earth processes, such as magma ocean formation and core separation, as well as ongoing processes within the modern mantle.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.

在某些类型的火山岩中测量钨元素的同位素组成非常重要，因为由于另一种元素铪 182 的同位素的放射性衰变，钨 182 同位素丰度的差异在地球历史的早期就出现了。 Hafnium-182 在太阳系历史中只存在了大约 7000 万年。这意味着一些结晶形成火山岩的岩浆来自 40 亿多年前形成的地幔内的某些地方，并且没有与其他地幔岩石混合。在这项研究中，将测量夏威夷群岛岩石中的钨同位素组成。研究表明，夏威夷群岛等火山洋岛岩石中钨的同位素组成各不相同。这项研究将测量的钨同位素变化将提供有关地球如何形成并分离成金属核、硅酸盐地幔和地壳的重要新信息。这些信息还将提供有关地幔这些古老部分可能在哪里以及它们如何最终形成火山岩的线索。这些结果将为模拟岩石运动和地幔熔化的科学家提供关于地球目前如何从内到外冷却自身的新见解。该项目将支持博士学位。学生和博士后研究员负责大部分工作，并且还将涉及本科生的贡献作为高级论文项目的一部分。 将对从一系列精心挑选的夏威夷熔岩中提取的钨进行高精度同位素分析，这些熔岩基于长寿命放射性同位素系统和微量元素丰度。马里兰大学实验室在过去十年中一直在此类钨同位素研究方面处于世界领先地位。先前已对各种地球化学信号进行了解释，以对各种回收和深层地幔成分进行采样。之前对海岛玄武岩以及其他类型的岩石（年轻和古老）的研究已经证明该实验室有能力从岩石中干净地分离出钨，并使用热电离质谱法进行高精度同位素测量。这项研究的主要目标是识别和解释小的钨同位素“异常”，并尝试将这些异常与其他地球化学示踪剂（例如 Nd、Pb 和 Os 同位素组成）联系起来，从而有可能在早期地球过程（例如岩浆海洋形成和核心分离，以及现代地幔内正在进行的过程）的时间和性质之间建立联系。该奖项反映了 通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。