Spatiotemporal Variability of Tungsten-182 in the Hawaiian Plume

University Of Maryland, College Park, College Park MD

Investigators

Abstract

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.