Grain-size reduction of feldspars by fracturing and neocrystallization in a low-grade granitic mylonite and its rheological effect

Jin Han Ree, Hyeong Soo Kim, Raehee Han, Haemyeong Jung

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42 Citations (Scopus)

Abstract

Feldspar grain-size reduction occurred due to the fracturing of plagioclase and K-feldspar, myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of K-feldspar porphyroclasts in the leucocratic granitic rocks from the Yecheon shear zone of South Korea that was deformed under a middle greenschist-facies condition. The neocrystallization of albitic plagioclase was induced by strain energy adjacent to the shear fractures and by chemical free energy due to the compositional disequilibrium between infiltrating Na-rich fluid and host K-feldspar. With increasing deformation from protomylonite to mylonite, alternating layers of feldspar, quartz and muscovite developed. The fine-grained feldspar-rich layers were deformed dominantly by granular flow, while quartz ribbons were deformed by dislocation creep. With layer development and a more distributed strain in the mylonite, lower stresses in the quartz-rich layers resulted in a larger size of dynamically recrystallized quartz grains than that of the protomylonite.

Original languageEnglish
Pages (from-to)227-237
Number of pages11
JournalTectonophysics
Volume407
Issue number3-4
DOIs
Publication statusPublished - 2005 Oct 7

Bibliographical note

Funding Information:
We thank W.M. Lamb and J. Newman for discussions on feldspar microstructures, and R. Guillemette and S. Choi for initial electron microprobe analyses on our samples. We appreciate thorough and constructive reviews by K. Kanagawa, an anonymous referee and J.-P. Burg which improved the paper significantly. This research was supported by KOSEF grant R02-2003-000-10039-0 to JHR.

Keywords

  • Dynamic recrystallization
  • Grain-size reduction
  • Granitic mylonite
  • Granular flow
  • Yecheon shear zone

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes

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