Abstract
The microstructures and rheology of quartz gouge (grain size < 130 μm), deformed under dry and hydrothermal conditions in experimental shear zones, are described. Layers ([sine wave] 0.3 μm) of quartz powder are sheared in a triaxial apparatus along 35° pre-cuts in diorite and sandstone cylinders. Specimens are sheared at effective confining pressures from 0 - 250 MPa, fluid pressures from 0 - 265 MPa, temperatures from 700 - 1000°C, and at constant axial strain rates from 10^-4 - 10^-6s^-1. Selected strain-rate-stepping texts are also described. Dry specimens exhibit only continuous, stable sliding. Increasing the temperature from 700 to 900°C produces an increase (up to 13%) in the sliding stress and the coefficient of friction. Cataclasis is the dominant mechanism of deformation in all dry tests, and deformation within the gouge is heterogeneous as evidenced by well developed Riedel fabrics. In wet specimens, stress-displacement curves are characterized by an abrupt initial stress drop followed by a period of stable sliding, or repeated abrupt stress drops (i.e., unstable sliding). Ultimate strength, sliding stress, and the magnitudes of stress drops decrease with decreasing effective confining pressure and increasing temperature. Sliding stability is enhanced as effective confining pressure decreases. Increasing temperature and strain rate also promote stable sliding. A transition from a negative to positive velocity dependence is observed between 800 and 900°C at effective confining pressures of 50 and 100 MPa. Specimens deformed in the presence of a pore fluid are texturally distinctive from dry counterparts. Wet specimens exhibit considerably more evidence of crystal-plastic and diffusion-dominated deformation; conspicuously less cataclasis and development of the Riedel fabric; and more homogeneously distributed deformation throughout the gouge. Growth of matrix grains into neoblasts and grain boundary mobility are greatly enhanced at high fluid pressures (Pf [greater than or equal to] 200 MPa), temperatures greater than 800°C, and at low strain rates. Neoblasts develop c-axis fabrics during deformation with most c-axes lying in the extensional quadrant of the strain ellipsoid...
Dula, William Frederick (1985). High temperature deformation of wet and dry artificial quartz gouge. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -410442.