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 > Timescales of spherulite crystallisation in obs...
View graph of relations

« Back

Timescales of spherulite crystallisation in obsidian inferred from water concentration profiles

Research output: Contribution to journalJournal article

Published

  • Jonathan M. Castro
  • Pierre Beck
  • Hugh Tuffen
  • Alexander R. L. Nichols
  • Douglas B. Dingwell
  • Michael C. Martin
Journal publication date12/2008
JournalAmerican Mineralogist
Journal number11-12
Volume93
Number of pages7
Pages1816-1822
Original languageEnglish

Abstract

We determined the kinetics of spherulite growth in obsidians from Krafla volcano, Iceland. We measured water concentration profiles around spherulites in obsidian by synchrotron Fourier transform infrared spectroscopy. The distribution of OH– groups surrounding spherulites decreases exponentially away from the spherulite-glass border, reflecting expulsion of water during crystallization of an anhydrous paragenesis (plagioclase + SiO2 + clinopyroxene + magnetite). This pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt. We modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary. Numerical models fit the natural data best when a small amount of post-growth diffusion is incorporated in the model. Comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size-dependent growth among a small population of spherulites.