5:15 PM - 7:15 PM
[SSS10-P29] Frictional behavior of cation-exchanged biotite
Keywords:Sheet silicate, Friction, Interlayer cation
Sheet silicates such as clay minerals play significant roles in deformation behavior of rocks due to their mechanical weakness. Cations on the sheet or in the layers are known to vary frictional strengths. Also, differences in crystal structures of sheet also have an influence on frictional strengths. This variety of frictional strengths of sheet silicates change the mechanical behavior of natural faults whose mineral compositions change with pressure and temperature conditions. Roles of the cations on/in the sheet and of the sheets themselves need to be separately understood because chemical composition of the sheet and its crystal structure change with diagenesis as well as cation species in natural systems.
In this study, we chemically weathered biotite using Na-TPB and EDTA and exchanged interlayer K into Na and water molecule (Kitayama et al., 2020; hereafter “Na-weathered biotite”). Friction experiments were performed on Na-weathered biotite as well as untreated biotite. We used an oil-medium triaxial deformation apparatus with direct shear assembly for the friction experiment. Effective normal stress and pore fluid pressure (with distilled water) of 20 and 10 MPa, respectively, were applied to the sample. Velocity step tests with 0.1-0.3-1-3 μm/s and slide-hold-slide tests with 30-100-300-1000-3000 seconds were performed.
Steady-state friction coefficients of Na-weathered biotite and original biotite were 0.18 and 0.40, respectively. The rate- and state-dependent friction (RSF) law parameter a were similar for both Na-weathered biotite and original biotite whereas Na-weathered biotite showed a smaller b than original biotite. The healing rate β was smaller for Na-weathered biotite than that for original biotite. Compared to cation-exchanged montmorillonite (e.g., Sakuma et al., 2022), this study shows a consistent trend that K-bearing sheet silicate has a higher frictional strength than Na-bearing sheet silicate. However, both Na-weathered biotite and original biotite showed higher friction coefficients than Na-montmorillonite and K-montmorillonite. This result indicates that both cations and chemical compositions of the sheet play roles in the frictional strengths of sheet silicate.
In this study, we chemically weathered biotite using Na-TPB and EDTA and exchanged interlayer K into Na and water molecule (Kitayama et al., 2020; hereafter “Na-weathered biotite”). Friction experiments were performed on Na-weathered biotite as well as untreated biotite. We used an oil-medium triaxial deformation apparatus with direct shear assembly for the friction experiment. Effective normal stress and pore fluid pressure (with distilled water) of 20 and 10 MPa, respectively, were applied to the sample. Velocity step tests with 0.1-0.3-1-3 μm/s and slide-hold-slide tests with 30-100-300-1000-3000 seconds were performed.
Steady-state friction coefficients of Na-weathered biotite and original biotite were 0.18 and 0.40, respectively. The rate- and state-dependent friction (RSF) law parameter a were similar for both Na-weathered biotite and original biotite whereas Na-weathered biotite showed a smaller b than original biotite. The healing rate β was smaller for Na-weathered biotite than that for original biotite. Compared to cation-exchanged montmorillonite (e.g., Sakuma et al., 2022), this study shows a consistent trend that K-bearing sheet silicate has a higher frictional strength than Na-bearing sheet silicate. However, both Na-weathered biotite and original biotite showed higher friction coefficients than Na-montmorillonite and K-montmorillonite. This result indicates that both cations and chemical compositions of the sheet play roles in the frictional strengths of sheet silicate.