Award Date

5-1-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Shichun Huang

Second Committee Member

Rodney Metcalf

Third Committee Member

Oliver Tschauner

Fourth Committee Member

Arya Udry

Fifth Committee Member

Clemens Heske

Number of Pages

195

Abstract

Earth’s mantle is the most voluminous part of the planet and is inaccessible to direct investigations. It is only possible to study it through indirect methods, such as the chemical makeup of erupted lavas. The Hawaiian Islands are thought to be the product of the mantle plume hypothesis, sometimes called a hot spot. Material from the Earth’s mantle is brought to the surface and erupted as magnesium rich lavas and form basalts. Hawaii is the longest lived active hot spot on Earth and makes it an ideal candidate for understanding the evolution of the Earth’s mantle and how lavas cool and crystallize. To that end, the Hawaii Scientific Drilling Project (HSDP) drilled and recovered over 3 km of basalts from Mauna Kea Volcano, Hawaii, to understand the evolution of a mantle plume volcano. This project investigates the different geochemical end-members that contribute to the shield stage of Mauna Kea Volcano, Hawaii, by analyzing the major and trace element compositions, as well as the radiogenic isotope (Sr-Nd-Hf-Pb) ratios of a unique series of shield stage basalts from HSDP called the high-CaO basalts. Their trace element concentrations are like that of rejuvenated stage basalts and their radiogenic isotope ratios fall within the range of rejuvenated stage basalts. I connect the high-CaO basalts to rejuvenated stage basalts through radiogenic isotope data and trace element modeling. In chapter 2, I show that the geochemical makeup of high-CaO basalts can be produced by melting a rejuvenated stage source to higher degrees. This suggests the same mantle source that produced rejuvenated lavas could have produced the high-CaO basalts, and that a depleted mantle component is intrinsic to the Hawaiian mantle plume that builds the shield stage. Kilauea Volcano on the island of Hawaii is the most active volcano on Earth and is currently erupting. It has been continuously sampled since its 1983 summit eruptions and allows us the rare opportunity to understand the real-time geochemical evolution of a volcano. Joint scientific ventures in the 2000s between the United States Geologic Survey and the Japan Marine Science and Technology Center, recovered by submersible submarine samples of Kilauea. Published age data show that some of the recovered submarine samples represent preshield ages, making Kilauea the only Hawaiian volcano that has both preshield and shield stage samples for study. In chapter 3, I show through new partial melting models that anomalous preshield Kilauea samples can be produced by low degree partial melts of a phlogopite-bearing source, and their sources have trace element patterns similar to that of high-CaO sources and could be the product of the same depleted end-member, meaning the depleted component universal in the mantle plume. The field of geochemistry has made leaps and bounds in the last two decades, particularly with the advent of multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS) that is capable of high precision stable isotope analysis. Magnesium is a major element and important geochemical parameter in monitoring the crystallization history of mafic lavas. Initial studies of magnesium isotopes showed no measurable variation in 26Mg. In chapter 4, I focus on lavas from Mauna Kea Volcano that transition from the tholeiitic shield stage to the more evolved, alkalic post-shield stage to monitor the effect of enhanced fractional crystallization. I present new 26Mg data for shield and postshield Mauna Kea lavas, in combination with thermodynamic MELTS models that show crystallization of oxide mineral phases can have fractionate stable isotopes of magnesium and can be used to detect the formation of these phases.

Keywords

Geochemistry; Hawaii; Mantle plume; Metal stable isotopes; Radiogenic isotopes

Disciplines

Geochemistry | Geology

File Format

pdf

File Size

9300 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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