HR: 15:25h
AN: T42D-08    [PDF]
TI: Nature and Origin of Cataclastic Bands in Well Cemented Quartz Arenite
AU: * Farver, J R
EM: jfarver@bgnet.bgsu.edu
AF: Bowling Green State University, Department of Geology, Bowling Green, OH 43403-0218 United States
AU: Onasch, C M
AF: Bowling Green State University, Department of Geology, Bowling Green, OH 43403-0218 United States
AB: Cataclastic bands are a common structure in well-cemented quartz arenites deformed at low temperatures ($<$250$\deg$C). These structures have been interpreted to originate by cataclasis with or without recrystallization. However, recent studies of samples from the Tuscarora and Oriskany sandstones from the Appalachian Valley and Ridge province suggest dilation was more important than shear in the formation of these bands. The cataclastic bands consist of sharply to diffusely-bounded tabular bodies ranging in thickness from 50 $\mu$m to a few cm filled with quartz having a uniform 5 $\mu$m grain size. In some cases, wall-parallel displacement can be demonstrated, but in others, the displacement is purely dilational. Two-phase, aqueous fluid inclusions in vuggy cores found in some bands yield homogenization temperatures of 140-170$\deg$C. FTIR data from traverses across cataclastic bands show a marked decrease in water content within the bands compared to nearby wall rock grains, and also suggest the presence of submicroscopic sheet silicates (mica or clays). In cathodoluminescence the bands are uniformly dark in contrast to brighter luminescing wall rock grains indicating either complete reconstitution of original wall rock or introduction of new phases. Rather than cataclasis, the fine grained texture in the bands is believed to result from rapid crystal growth in a dilating fracture with variable, but small amounts of shear. Despite the fine grained texture, the presence of sheet silicates suggests that these bands may have acted as a fluid conduit, not a permeability barrier.
DE: 8010 Fractures and faults
DE: 8020 Mechanics
DE: 8030 Microstructures
DE: 8045 Role of fluids
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting