Mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20–600°C: Implications for natural faults in limestones

摘要: We report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures (T) within the range from 20° to 600 °C. The were wet, using pore fluid pressures (Pf) of 10 ≤ Pf ≤ 60 MPa. One series employed a constant effective normal stress ( σneff) 50 MPa, while in second σneff was sequentially stepped 30 100 MPa. In all experiments, sliding velocity (v) 0.03 100 µm/s. results showed stable, strengthening behavior 20 °C, but weakening 100° 550 °C (for v-steps <3 µm/s), which frequently accompanied by stick–slip. At 600 °C, occurred. Microstructural observations suggest increasing importance ductile deformation with temperature, as reflected localized band structure 20 °C giving way pervasive, shear-plane-parallel grain shape fabric Using existing flow equations for dense polycrystals, we show that dislocation and/ or diffusion creep 10–30 µm sized bulk gouge grains likely played role T ≥ 400 °C. observed can be explained slip-mechanism involving dilatant granular competition creep-controlled compaction. Our have important implications breadth seismogenic zone limestone terrains, and interpretation natural rock microstructures. Specifically, samples sheared 400-550 °C exhibited essentially brittle/ frictional mechanical (stick–slip), corresponding microstructures resembled mylonite.