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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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:
Journal 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:
?? obsidianspheruliteoxidation-reductionftirironhydrogenxanesgeochemistry and petrologygeologyge environmental sciences ??
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Deposited On:
05 Oct 2009 14:25
Last Modified:
27 Feb 2024 00:42