Effect of clay content and mineralogy on frictional sliding behavior of simulated gouges: Binary and ternary mixtures of quartz, illite, and montmorillonite

Abstract

[1] We investigated the frictional sliding behavior of simulated quartz-clay gouges under stress conditions relevant to seismogenic depths. Conventional triaxial compression tests were conducted at 40 MPa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz, montmorillonite, and illite. In all cases, frictional strengths of mixtures fall between the end-members of pure quartz (strongest) and clay (weakest). The overall trend was a decrease in strength with increasing clay content. In the illite/quartz mixture the trend was nearly linear, while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted.Microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers. Two micromechanical models were used to analyze the critical clay fractions for the two-regime transitions on the basis of clay porosity and packing of the quartz grains. The transition from regime 1 (high strength) to 2 (intermediate strength) is associated with the shift from a stresssupporting framework of quartz grains to a clay matrix embedded with disperse quartz grains, manifested by the development of P-foliation and reduction in Riedel shear angle. The transition from regime 2 (intermediate strength) to 3 (low strength) is attributed to the development of shear localization in the clay matrix, occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness. Our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects.

Strain localization during high temperature creep of marble: The effect of inclusions

“…Application of equations (3) and (4) assumes a full (laterally unconstrained) split cylinder sample assembly configuration with constant inclusion thickness and contact area (Tembe et al, 2010).…”

Creating the link between micro-seismic observations and hydro-mechanical changes in the reservoir

“…An example of laboratory data recording the behavior of sheared clayey materials is shown at left from Fig. 3 of Ikari [41]; many other experiments exist [42][43][44][45]. Shear--induced permeability decrease is consistently observed in clayey materials, indicating that though one may accomplish plastically, aseismically, slow--slip regions in such materials [40], the accompanying permeability changes would be deleterious to production goals.…”

The influence of organic–rich shear zones on pelagic sediment deformation and seismogenesis in a subduction zone

“…Deformation, in such a case, becomes controlled by the mechanical properties of the clay matrix and the CM. Artificial mixtures of quartz and illite gouge exhibit a gradual but constant decrease of shear strength as a function of illite content (Brown et al, 2003;Tembe et al, 2010). In addition, several experimental works have shown that clay-rich fault rocks have velocity-strengthening properties (e.g., Saffer and Marone, 2003;Ikari et al, 2011).…”

“…A number of experiments quantitatively demonstrate how frictional behavior changes when weak materials such as clay minerals and graphite are included in the samples (Logan and Rauenzahn, 1987;Brown et al, 2003;Takahashi et al, 2007;Crawford et al, 2008;Tembe et al, 2010;Oohashi et al, 2013). Several studies show that as little as~10% of these materials is enough to act as a lubricant (e.g., Collettini et al, 2009;Oohashi et al, 2013).…”