Diffusion and partitioning of magnesium in quartz grain boundaries

Jay Thomas, E. Bruce Watson

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Experiments were conducted to study Mg diffusion in quartz grain boundaries. A detector particle method was used to study grain-boundary diffusion because Mg was confined exclusively to the grain boundaries. Diffusion couples were assembled by placing a MgF2 disk against a disk of quartzite, which was placed against a disk of quartzite that contained fayalite (Fe2SiO4) ‘detector particles.’ During diffusion experiments, Mg diffused along the grain boundaries of the central quartzite toward the fayalite quartzite where it was incorporated into fayalite detector particles. The only pathway for transport from the diffusant source to fayalite detector particles was through the grain boundaries in the central quartzite. The cross-sectional area of the grain boundaries that delivered Mg to the fayalite detector particles was determined from scanning electron microscope images. The Mg contents of the fayalite detector particles were used to calculate the mass of Mg that fluxed through the grain boundaries. During the diffusion experiments, pyroxene crystallites nucleated and grew in the central quartzites from Mg and Fe that was transported along quartz grain boundaries. The Mg contents of the crystallites vary linearly throughout the quartzites, suggesting that steady-state transport conditions were rapidly established in the quartz grain boundaries. Magnesium concentrations in the pyroxene crystallites are proportional to concentration gradients in the grain boundaries of the central quartzite. Grain-boundary fluxes and linear concentration gradients were used to calculate diffusion of Mg in grain boundaries of the central quartzite component in the diffusion couples.

Original languageEnglish (US)
Pages (from-to)1-12
Number of pages12
JournalContributions to Mineralogy and Petrology
Volume168
Issue number4
DOIs
StatePublished - Oct 1 2014
Externally publishedYes

Fingerprint

Quartz
grain boundary
Magnesium
magnesium
Grain boundaries
quartzite
partitioning
quartz
grain boundaries
fayalite
Particle detectors
radiation counters
Crystallites
crystallites
pyroxene
gradients
experiment
Experiments
detector
particle

Keywords

  • Diffusion
  • Experimental study
  • Geochemistry
  • Grain boundary
  • Grain-boundary diffusion
  • Grain-boundary partitioning
  • Grain-boundary segregation
  • Quartz
  • Type-C kinetics

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Diffusion and partitioning of magnesium in quartz grain boundaries. / Thomas, Jay; Watson, E. Bruce.

In: Contributions to Mineralogy and Petrology, Vol. 168, No. 4, 01.10.2014, p. 1-12.

Research output: Contribution to journalArticle

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