Title of article :
Spherulite crystallization induces Fe-redox redistribution in silicic melt
Castro، نويسنده , , Jonathan M. and Cottrell، نويسنده , , Elizabeth and Tuffen، نويسنده , , Hugh and Logan، نويسنده , , Amelia V. and Kelley، نويسنده , , Katherine A.، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2009
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 obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late-stage crystallization to the redox signature of glassy lavas.
obsidian , oxidation–reduction , Spherulite , FTIR , XANES
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