Spatiotemporal Variability of Tungsten-182 in the Hawaiian Plume

钨元素的同位素组成对测量某些类型的火山岩很重要，因为钨-182同位素丰度的差异在地球历史上很早就出现了，这是由于另一种元素铪-182的同位素的放射性衰变。铪-182仅在太阳系历史的前7000万年中存在。这意味着一些结晶形成火山岩的岩浆来自40多亿年前形成的地幔内部，并且没有与其他地幔岩石混合。为了这项研究，钨的同位素组成将在夏威夷群岛的岩石中进行测量。研究表明，来自夏威夷群岛等火山海洋岛屿的岩石中钨的同位素组成各不相同。这项研究测量的钨同位素变化将提供重要的新信息，说明地球是如何形成并分离成金属地核、硅酸盐地幔和地壳的。这些信息还将提供线索，说明这些古老的地幔部分可能在哪里，以及它们是如何在火山岩中结束的。这些结果将为模拟地幔中岩石运动和融化物的科学家提供新的见解，让他们了解地球目前是如何从内到外冷却的。该项目将支持一名博士生和一名博士后研究助理进行大部分的研究，也将涉及一名本科生作为高级论文项目的一部分的贡献。根据长寿命放射性同位素系统和微量元素丰度，将对从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。在过去的十年里，马里兰大学的实验室在这种类型的钨同位素研究方面一直处于世界领先地位。各种地球化学信号以前被解释为各种循环和深部地幔成分的样本。先前对海洋岛屿玄武岩以及其他类型的岩石（年轻的和古老的）的研究表明，该实验室有能力从岩石中彻底分离钨，并使用热电离质谱法产生高精度的同位素测量结果。这项研究的主要目标是识别和解释小的钨同位素“异常”，并试图将这些异常与其他地球化学示踪剂（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（如岩浆海洋形成和岩心分离）的时间和性质以及现代地幔内正在进行的过程之间建立联系。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 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.