Icelands great abundance of silicic rock (10-13% of subaerial exposures), coupled with the unusual thickness of the islands crust, hints at continental nucleation and permanent crust construction in an oceanic environment. This phenomenon is rare on modern Earth, but it is often postulated that Icelandic magmatism is a modern analogue for ancient (Hadean) crustal construction. Understanding the processes that form abundant, juvenile, silicic crust in oceanic Iceland has important implications for understanding Earths early, and ongoing, history.
The Icelandic crust is juvenile; there is neither ancient nor appreciable felsic crust nor sediments to complicate the magmatic history. Investigations into the origins of Icelandic silicic magma are therefore more focused than the global approach to the issue. Despite this, the issue remains highly contentions and hotly debated.
Studies of zircon have elsewhere underpinned understanding of silicic magma processes and crustal evolution, but no such research has been carried out in Iceland until now. This investigation into the origins and evolution of Icelands silicic crust is the first comprehensive study of Icelandic zircons. Elemental and isotopic geochemistry and U-Th-Pb geochronology of zircon from intrusive and extrusive rocks and sediments, coupled with supporting bulk-rock elemental and isotope geochemistry and petrography, reveal that: (1) very low 18O/16O supports partial melting of crust hydrothermally altered by meteoric water as a primary driver of Icelandic felsic petrogenesis; (2) uniformity of O isotopic compositions demonstrates neither a change in magmatic processes nor a change in the meteoric-water composition imprinted on magmas throughout Icelands history, despite extreme climate variability; (3) increased variability in Hf isotope ratios suggest changes to Icelands mantle source with time, (4) Iceland is not an appropriate modern analogue for the Hadean, as their zircon records are quite distinct; (5) zircons reflect tens of thousands of years of activity preceding individual rhyolitic eruptions, and indicate the longevity of silicic magma systems at individual central volcanoes may reach three million years; (6) Icelandic zircons form a compositional category that is distinguishable from typical continental and oceanic zircon populations.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-07172014-180040 |
| Date | 22 July 2014 |
| Creators | Carley, Tamara Lou |
| Contributors | Eugene J. LeBoeuf, James H. Clarke, David J. Furbish, Guilherme A.R. Gualda, Calvin F. Miller |
| 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-07172014-180040/ |
| Rights | restricted, 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. |
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