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Author ORCID Identifier

https://orcid.org/0000-0002-8002-4832

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Geosciences

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

Sheila Seaman

Second Advisor

Christopher Condit

Third Advisor

Alan Richmond

Fourth Advisor

Laurie Brown

Subject Categories

Geochemistry | Geology | Volcanology

Abstract

Icelandic basalts were long thought to be low in water (e.g. Gunnarsson et al., 1998), but more recent studies suggest that hotspots, like the Iceland mantle plume, may be a source of hydrous basaltic melts (Nichols et al., 2002). To explore a possible link between location, volatile concentration and resulting petrogenetic implications, samples were collected from eleven volcanic centers throughout Iceland. Water concentrations were measured in melt inclusions and phenocrysts using Fourier transform infrared (FTIR) spectroscopy. Results for a subset of samples indicate variable water in melt inclusions ranging from approximately 50 ppm to over 3000 ppm. Samples from southwestern Iceland along the West Volcanic Zone and Reykjanes Volcanic Belt, on average, have water concentrations of up to 4 times as much as samples collected elsewhere. There is evidence for a geographic trend of increasing water concentration with distance away from the mantle plume, implying a dry plume.

The Springerville Volcanic Field (SVF), located in east-central Arizona is an intraplate, monogenetic volcanic field. Our magmatic mapping focuses on delineating and characterizing individual magmatic units and placing them into a temporal framework, providing an organizational model for the study of similar fields. Results from the 501 units mapped in the SVF, characterized by 565 geochemical samples offer insights into the evolution of SVF magmas. Of the 12 lithologic classes we defined, olivine phyric lavas are most abundant followed by diktytaxitic and olivine-plagioclase units. Younger units are smaller in area with more evolved lithologies ranging from aphyric to feldspathic basalts. Eruptions in the SVF progressed from early large-volume tholeiitic eruptions that became increasingly alkalic with time. Tholeiite pressure-temperature estimates and geochemical data suggest a shallower enriched mantle (EM) lithospheric source from higher degrees of partial melting. Basanites, alkali olivine basalts and transitional basalts originate from a deeper, PREMA-like asthenospheric source. The geochemical signature of the silica-undersaturated basanites is not inconsistent with a carbonated source. The more evolved alkalic rocks are derived at shallower, lithospheric pressures but show isotopic and trace element similarities to the deeper, asthenospheric sourced magmas suggesting possible mixing between deeper, basanitic magmas and tholeiitic magmas in the lithosphere.

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