Journal
JOURNAL OF STRUCTURAL GEOLOGY
Volume 29, Issue 12, Pages 1872-1881Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2007.09.011
Keywords
quartz-muscovite mylonite; dynamic recrystallization; grain size; second-phase particles; particle dispersion; deformation mechanism
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Quartz ribbons in a quartz-muscovite mylonite from the Sunchang shear zone of South Korea show a variation in the average size (25-107 mu m) 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 mu m, whereas those along the quartz grain boundaries range from 2 to 98 mu m. The average quartz grain size (D) calculated from three-dimensional grain size distribution decreases drastically with increasing mica volume fraction (F-m) up to F-m = 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 x InFm - 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 F-m > 3%, presumably due to the greater contribution to the total deformation of grain boundary sliding for quartz with a smaller grain size (D < 47 mu m). (C) 2007 Elsevier Ltd. All rights reserved.
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