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Spherulite crystallization induces Fe-redox redistribution in silicic melt.

Castro, Jonathan M. and Cottrell, Elizabeth and Tuffen, Hugh and Logan, Amelia and Kelley, Katherine A. (2009) Spherulite crystallization induces Fe-redox redistribution in silicic melt. Chemical Geology, 268 (3-4). pp. 272-280. ISSN 0009-2541

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    Abstract

    Rhyolitic obsidians from Krafla volcano, Iceland, record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt. We performed synchrotron µ-FTIR and µ-XANES measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones. Measurements show that the colorless glass is enriched in OH-groups and depleted in ferric iron, while the brown glass shows the opposite relationship. The color shift between brown and clear glass is sharp, suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization. We conclude that the most likely reducing agent is hydrogen, produced by magnetite crystallization within the spherulite. The Krafla flow dramatically captures redox disequilibrium on the micoscale and highlights the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas.

    Item Type: Article
    Journal or Publication Title: Chemical Geology
    Additional Information: The final, definitive version of this article has been published in the Journal, Chemical Geology 268 (3-4), 2009, © ELSEVIER.
    Uncontrolled Keywords: Obsidian ; spherulite ; oxidation-reduction ; FTIR ; iron ; hydrogen ; XANES
    Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 27160
    Deposited By: Dr Hugh Tuffen
    Deposited On: 05 Oct 2009 15:25
    Refereed?: Yes
    Published?: Published
    Last Modified: 26 Jul 2012 16:39
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/27160

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