HR: 1340h
AN: T53C-1455    [Abstracts]
TI: Effect of Mica on Grain Size of Dynamically Recrystallized Quartz in Mylonite
AU: * Ree, J
EM: reejh@korea.ac.kr
AF: Department of Earth and Environmental Sciences, Korea University, Anam-dong, Seongbuk-gu, Seoul, 136-701 Korea, Republic of
AU: Song, W
EM: wjkm@korea.ac.kr
AF: Department of Earth and Environmental Sciences, Korea University, Anam-dong, Seongbuk-gu, Seoul, 136-701 Korea, Republic of
AU: Jung, H
EM: haemyeong.jung@ucr.edu
AF: Institute of Geophysics and Planetary Physics, University of California, 1432 Geology Building, Riverside, CA 92521 United States
AB: Quartz ribbons in quartz-muscovite mylonite from the Honam shear zone of South Korea show a size variation of dynamically recrystallized quartz depending on fraction, size and distribution of mica. The quartz ribbons in muscovite matrix are 0.13 to 0.88 mm thick with axial ratio of 7 to 12. Quartz grains (5 to 200 μm) within the ribbons mostly have wavy or lobate boundaries with a grain-shape preferred orientation oblique to mylonitic foliation. The quartz grains show sweeping undulose extinction, deformation bands, tabular or equiaxed subgrains and a lattice preferred orientation. Micas within quartz ribbons occur both within quartz grains and along quartz grain boundaries, having a strong preferred orientation with their basal planes parallel to the mylonitic foliation. Micas (or mica aggregates) inside quartz show a size range of 1 to 25 μm, whereas those along quartz grain boundaries have a size range of 2 to 98 μm. The average grain size of quartz (D) decreases drastically with increasing mica fraction (Fm) up to Fm = 10% in the ribbons, and further increase in mica fraction above 10% results in only a little decrease (with some fluctuation) in quartz grain size, generating an equation of D = -10.7 × ln(Fm) + 8.3. With almost the same fraction of mica, however, quartz ribbons with dispersed mica show a smaller grain size of quartz than those with clustered mica, indicating importance of the distribution of second-phase particles to the grain size of dynamically recrystallized quartz. The lattice preferred orientation of quartz becomes much weaker with Fm > 10%, presumably due to more contribution of grain boundary sliding of quartz with a smaller grain size (D < 30 μm) to the total deformation.
DE: 8000 STRUCTURAL GEOLOGY
DE: 8012 High strain deformation zones
DE: 8030 Microstructures
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: Fall Meeting 2005