HR: 17:00h
AN: NG12C-05    [PDF]
TI: Differing Comminution Characteristics of Quartz and Feldspar in Westerly Granite Simulated Gouge
AU: * Konkachbaev, A I
EM: aikonk01@louisville.edu
AF: Anouar Konkachbaev, Computer Science and Enginiring, Speed Scientific School, University of Louisville , Louisville, KY 40292 United States
AU: Hadizadeh, J
EM: hadizadeh@louisville.edu
AF: Jafar Hadizadeh, Department of Geography & Geosciences, Louisvile, KY 40292 United States
AU: Tullis, T E
EM: Terry_Tullis@brown.edu
AF: Terry Tullis, Department of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Beeler, N M
EM: nbeeler@usgs.gov
AF: Nick Beeler, USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: BSE images of the gouge (35% K$-$feldspar, 32% plagioclase, 28% quartz, 5% mica; particle size $\leq$88$\mu$m) deformed in rotary frictional sliding at room temperature and 25MPa normal stress were studied at 250x, 500x, and 1000x magnification. We quantified changes in size and shape of the gouge particles as a whole and quartz and feldspar particles separately in samples with 3, 10, 65, and 409mm displacement. Following binarization, semi-thresholding technique was used to resolve K-feldspar particles from total image. We developed a particle pixel-averaging algorithm to resolve quartz from plagioclase feldspar, and new shape descriptor Particle Outline Linearity (POL) for relatively precise quantification of shapes of particles $\geq$500 pixels (1-4$\mu$m). Results correlate sequence of texture images, particle size distribution (PSD), fractal dimension (D), and POL data with shear displacement. As represented by changes in D, particle size reduction rate with respect to shear displacement (rate of comminution) is higher for quartz than feldspar. For the applied range of shear displacement quartz and feldspar appear to have different but converging PSD in the same gouge. Log-linear fit to the data suggests that D=2.6 distribution is achieved in 3-5mm of shear first in the whole gouge followed by feldspars while quartz PSD does not attain the value until $\sim$25mm of shear displacement. POL data indicates that Quartz and feldspar particle shapes begin to diverge within the initial 10mm of displacement. Feldspars becoming more angular while quartz particles tend to become rounder. In view of the POL data we interpret the comminution rate difference as follows. Cleavage fracture is effective in reducing the size of largest feldspar particles resulting in a wider size range and lower D values than quartz. Largest quartz particles, however, tend to become round by indentation fracture and abrasion, shedding small fragments in the process. Quartz PSD thus tends to become almost bimodal with a fraction of smaller particles that progressively result in higher D values. Size modality differences between quartz and feldspar are evident on most of the texture images. This preliminary study provides some microstructural basis for explaining differences in laboratory frictional behavior and development of localization structures between quartz and granitic gouges.
UR: http://www.louisville.edu/~j0hadi01/
DE: 3900 MINERAL PHYSICS
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 8100 TECTONOPHYSICS
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting