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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Spherulite crystallization induces Fe-redox redistribution in silicic melt.
AU - Castro, Jonathan M.
AU - Cottrell, Elizabeth
AU - Tuffen, Hugh
AU - Logan, Amelia
AU - Kelley, Katherine A.
N1 - The final, definitive version of this article has been published in the Journal, Chemical Geology 268 (3-4), 2009, © ELSEVIER.
PY - 2009/11/30
Y1 - 2009/11/30
N2 - 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.
AB - 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.
KW - Obsidian
KW - spherulite
KW - oxidation-reduction
KW - FTIR
KW - iron
KW - hydrogen
KW - XANES
U2 - 10.1016/j.chemgeo.2009.09.006
DO - 10.1016/j.chemgeo.2009.09.006
M3 - Journal article
VL - 268
SP - 272
EP - 280
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
IS - 3-4
ER -