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Investigations of Southwest Pacific Intraplate and Backarc Volcanism using Traditional and Non-Traditional Isotopes.

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Title:Investigations of Southwest Pacific Intraplate and Backarc Volcanism using Traditional and Non-Traditional Isotopes.
Authors:Finlayson, Valerie A.
Contributors:Geology & Geophysics (department)
Date Issued:Aug 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Volcanic activity in the southwest Pacific Ocean provides ample opportunity
to study various tectonic settings spanning as much as ~140 million years. Highprecision
stable and radiogenic isotopes are powerful geochemical tools capable of
identifying melt source contributions and petrological processes in mantle-derived
melts in various tectonic settings, expanding our understanding of the dynamics of
underlying Pacific mantle domains.
In this dissertation, I present methodological improvements to Fe isotopic
measurement methods capable of achieving an analytical precision of ±0.046‰. An
accompanying secondary statistical correction can account for instrumental drift
between analyses. At such high precision, potential exists to resolve Fe isotope
fractionation behavior in response to processes such as melting, fractionation, and
metasomatism in ultramafic materials. Predictable Fe isotope behavior can also be
used to identify isotopically distinct source compositions contributing to mantlederived
melts. Here, Fe isotope behavior is characterized in a suite of young
boninitic melts from the Mata Volcanic Field, located in the northeastern Lau Basin.
The combination of δ56Fe and melt compositions suggest that Mata volcanoes see
variable input from a subduction fluid-like component, and the degree of its
contribution may be influenced by proximity to the Tonga forearc versus nearby
backarc basin spreading centers.
The isotopically distinct, long-lived (120+ Myr) Rurutu hotspot track is a
third potential constraint to hotspot-based Pacific absolute plate motion models,
which are subject to large model uncertainty, particularly after ~47-50 Ma. Located
in a geologically complex region of the southwest Pacific known as the “Hotspot
Highway”, other hotspot tracks overlap with the Rurutu track, requiring use of
radiogenic (Sr-Pb-Nd-Hf) isotope ratios to identify Rurutu-origin seamounts. Paired
with 40Ar-39Ar age data, I present evidence of age-progressive (~75-42 Ma), dual
track Rurutu volcanism in the Tuvalu chain. Additionally, I present a computational
method that identifies the highest-probability location and age of the Rurutu Bend,
analogous to the ~47-50 Ma Hawaiian-Emperor Bend. Identification of this ~50-49
Ma Bend in the Rurutu hotspot track confirms the continuity of Rurutu volcanic
activity throughout the Pacific ocean basin, establishing its importance as a third
major, singly-sourced constraint on Pacific absolute plate motion.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Geology and Geophysics

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