This two-part study is focused on the evolution of silicic magma in two very different settings. The first part is a study of zircon to understand the generation, storage, and evolution of felsic magmas erupted in historical times in Iceland. Icelandic zircon compositions, which are correlated with proximity to the main axial rift, are distinct from those of continental zircon. Icelandic zircon exhibit generally low U (<200 ppm), low U/Th (<1), low Hf (<10,000 ppm) and uniformly high Ti (>10 ppm). Ti concentrations imply that zircon grew at relatively high temperatures (800-950 °C). U-Th ages demonstrate the range of ages is far less than is common in continental settings, but zircon growth predates eruptions by thousands to tens of thousands of years. These magmas did not evolve by monotonic fractionation, but experienced zircon entrainment and open-system magma recharge. The second part of this study is a modeling project focused on better understanding the conditions that lead to the evolution and destabilization of the Peach Spring Tuff (AZ, CA, NV) in particular, and large (super-eruption) silicic magmas in general. Analyses of pumice and fiamme from intracaldera and outflow exposures reveal systematic heterogeneity in the underlying chamber at the time of eruption. Whole-rock compositions and modeling results are compatible with differentiation in a shallow magma reservoir at ~200-300 MPa. Destabilization of this large chamber appears to be strongly related to the timing of water saturation relative to other phases and to the pseudo-invariant, both of which are correlated with pressure and water content. Changes in total magma volume and density are modest for systems with high initial water contents (7 wt. %) and significant for systems with low initial water (2-3 wt. %). In the latter case, crystallization and bubble exsolution likely promote magma destabilization and eruption.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-07092010-143700 |
| Date | 16 July 2010 |
| Creators | Carley, Tamara Lou |
| Contributors | Calvin F. Miller, Guilherme A.R. Gualda |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-07092010-143700/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.2467 seconds