Effect of mica on the grain size of dynamically recrystallized quartz in a quartz-muscovite mylonite

Won Joon Song, Jin Han Ree

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Quartz ribbons in a quartz-muscovite mylonite from the Sunchang shear zone of South Korea show a variation in the average size (25-107 μm) of dynamically recrystallized quartz depending on the fraction and dispersion of muscovite within the ribbons. Micas within the quartz ribbons occur both inside quartz grains and along their boundaries, having a strong preferred orientation with the basal planes parallel to the mylonitic foliation. Micas (or mica aggregates) inside the quartz show a size range of 1-25 μm, whereas those along the quartz grain boundaries range from 2 to 98 μm. The average quartz grain size (D) calculated from three-dimensional grain size distribution decreases drastically with increasing mica volume fraction (Fm) up to Fm = 3% in the ribbons, and further increases in the mica fractions above 3% result in only a little decrease (with some fluctuation) in the quartz grain size, generating the equation of D = -20.11 × lnFm - 9.64. With almost the same fraction of mica however, the quartz ribbons with dispersed mica show a smaller quartz grain size than those with clustered mica, indicating the importance of dispersion as well as fraction of second-phase particles to the grain size of dynamically recrystallized quartz. Quartz c-axes tend to have a random orientation with an Fm > 3%, presumably due to the greater contribution to the total deformation of grain boundary sliding for quartz with a smaller grain size (D < 47 μm).

Original languageEnglish
Pages (from-to)1872-1881
Number of pages10
JournalJournal of Structural Geology
Volume29
Issue number12
DOIs
Publication statusPublished - 2007 Nov

Keywords

  • Deformation mechanism
  • Dynamic recrystallization
  • Grain size
  • Particle dispersion
  • Quartz-muscovite mylonite
  • Second-phase particles

ASJC Scopus subject areas

  • Geology

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