PETROGENESIS OF BASALTIC LAVAS IN ICELAND AND THE SPRINGERVILLE VOLCANIC FIELD, U.S.A.: THE INFLUENCE OF TECTONIC SETTING, DEPTH OF MELTING AND VOLATILES
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 a...
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ScholarWorks@UMass Amherst
2019
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| Online Access: | https://scholarworks.umass.edu/dissertations_2/1798 https://doi.org/10.7275/15154705 https://scholarworks.umass.edu/context/dissertations_2/article/2785/viewcontent/Dissertation_Final_9_12.pdf |
| Summary: | 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 ... |
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