Experimental Insights Into Fault Reactivation and Stability of Carrara Marble Across the Brittle–Ductile Transition

Abstract

Little is known about the impact of pressure (P) and temperature (T) on faulting behavior and the transition to fault locking under high P–T conditions. Using a Paterson gas‐medium apparatus, triaxial compression experiments were conducted on Carrara marble (CM) samples containing a saw‐cut interface at ∼40° to the vertical axis at a constant axial strain rate of ∼1 × 10⁻⁵ s⁻¹, P = 30–150 MPa and T = 20–600°C. Depending on the P–T conditions, we observed the complete spectrum of deformation behavior, including macroscopic (shear) failure, stable sliding, unstable stick‐slip, and bulk deformation with locked faults. Macroscopic failure and stable sliding were limited to P < 100 MPa and T = 20°C. In contrast, at P ≥ 100 MPa or T ≥ 500°C, faults were locked, and samples with bulk deformation experienced strain hardening at strains ≤8.8%. At T = 100–400°C and P ≤ 100 MPa, we observed unstable stick‐slip behavior, where both fault reactivation stress and subsequent stress drop increased with increasing pressure and temperature, associated with increasing matrix deformation and less fault slip. Microstructures indicate a mixture of microcracking, twinning and dislocation activity (e.g., kinking and undulatory extinction) that depends on P–T conditions and peak stress. The transition from slip to lock‐up with increasing pressure and temperature is induced by an enhanced contribution of crystal plastic deformation. Our results show that fault reactivation and stability in CM are significantly influenced by P–T conditions, probably limiting the nucleation of earthquakes to a depth of a few kilometers in calcite‐dominated faults.