12,000

We have over 12,000 students, from over 100 countries, within one of the safest campuses in the UK

93%

93% of Lancaster students go into work or further study within six months of graduating

Home > Research > Publications & Outputs > Spherulite crystallization induces Fe-redox red...
View graph of relations

« Back

Spherulite crystallization induces Fe-redox redistribution in silicic melt.

Research output: Contribution to journalJournal article

Published

  • Jonathan M. Castro
  • Elizabeth Cottrell
  • Hugh Tuffen
  • Amelia Logan
  • Katherine A. Kelley
Journal publication date30/11/2009
JournalChemical Geology
Journal number3-4
Volume268
Number of pages9
Pages272-280
Original languageEnglish

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.

Bibliographic note

The final, definitive version of this article has been published in the Journal, Chemical Geology 268 (3-4), 2009, © ELSEVIER.