Files and links (1)
Free to read and download, Open Access
Thesis
Uranium series analysis of 2006 Augustine volcanics: an investigation into the timescales of magmatic processes
University of Iowa
Master of Science (MS), University of Iowa
Spring 2011
DOI: 10.17077/etd.k8kl7gj4
Abstract
<p>The purpose of this study is to constrain the mode and tempo of the processes that generated lavas erupted in 2006 eruption from Augustine Volcano, Alaska. There have been 5 eruptions from Augustine over the last century that ejected andesitic to dacitic lava domes and pyroclastic flows. The short recurrence interval of Augustine, in conjunction with the variety of differentiated magma involved in each eruption makes Augustine an ideal location to study magmatic processes such as magma production, magma mixing, magma differentiation, and shallow degassing occurring over the decadal time-scales in explosive subduction-related volcanoes. Toward this end, 2006 Augustine ejecta were analyzed for abundances of short and long-lived U-series nuclides including 238U, 230Th, 226Ra, and 210Pb as well as the abundances of a complete suite of major and trace elements.</p>
<p>Samples from Augustine have nearly constant Th/U rations, but excesses of (230Th) over (238U) that vary more than the analytical error. Based on documentation for basaltic parental magmas (Larsen et al., 2010) and a lack of evidence for garnet fractionation in differentiated magmas, variations in (230Th/232Th) values for Augustine magmas appear to result from mixing melts and crystals, which have average ages as high as 54 Ka.</p>
<p>Our most mafic sample (an enclave with 53 wt % SiO2) has (226Ra/230Th) = ~1.2. With increasing concentrations of SiO2, the (226Ra/230Th) values decrease to ~1 at SiO2 ~ 56 wt%, increase to 1.45 at SiO2 ~ 59 wt%, then decrease to ~1 in samples with >61 wt. % SiO2. These data suggest that three magmas mingled and mixed during the 2006 eruption: basaltic andesites with Ra excesses generated by mantle melting; a 59 wt% SiO2 magma with 226Ra excesses generated from incongruent melting of young plutonic materials, and 61-62 wt % SiO2 andesites with relatively long crustal residence times.</p>
<p>Excesses of (210Pb) over (226Ra) were measured in the most mafic and silicic samples at Augustine, whereas intermediate samples had either equilibrium (210Pb/226Ra) or small 210Pb deficits. The excesses in the basaltic andesites were likely generated during degassing within a compositional boundary layer. Excesses in high silica samples were likely produced by localized degassing through porous networks of vesicles.</p>
Details
- Title: Subtitle
- Uranium series analysis of 2006 Augustine volcanics: an investigation into the timescales of magmatic processes
- Creators
- Jennifer Ann Thompson - University of Iowa
- Contributors
- Mark K. Reagan (Advisor)David Peate (Committee Member)Michael Rowe (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Spring 2011
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.k8kl7gj4
- Number of pages
- ix, 136 pages
- Copyright
- Copyright 2011 Jennifer Ann Thompson
- Language
- English
- Description bibliographic
- Includes bibliographical references (pages 130-136).
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983776947602771
Metrics
263 File views/ downloads
142 Record Views