UNRAVELING CHEMICAL-MECHANICAL FAULT DEFORMATION PROCESSES IN CARBONATE ROCKS

Calcite-bearing rocks, such as limestones, chalks, and marbles, provide a unique opportunity to investigate the interplay of brittle, plastic, and fluid-mediated deformation processes within basins and along fault zones. Calcite is highly reactive, prone to crystal plasticity, and undergoes complex chemical-mechanical deformation under modest upper-crustal temperatures and pressures. This investigation seeks to disentangle the chemical-mechanical deformation processes in calcite-bearing rocks by combining laboratory experiments and natural sample analyses, with a focus on microstructural proxies to infer deformation mechanisms and conditions.

Laboratory deformation experiments under controlled stress and fluid chemistry followed by microstructural analyses, including Electron Backscatter Diffraction (EBSD) and Laue X-ray microdiffraction, are utilized to capture grain-scale deformation and residual strains. Complementary experiments using nitratine (NaNO3), an analog to calcite, simulate higher-temperature and lower strain-rate conditions. These controlled experiments are paired with the analysis of naturally deformed calcite samples from diverse tectonic settings.

Preliminary results demonstrate the influence of fluid chemistry on deformation mechanisms. Manganese-doped experiments showing an unexpected increase in dislocation creep deformation. This increase is evident through three distinct analyses: 1) qualitative imagery, 2) heightened low-angle disorientation clusters, and 3) a distinct Crystallographic Vorticity Analysis (CVA) distribution. Further, the manganese-doped sample had a marked decrease in twin density with respect to our control sample, where the non-doped samples exhibited a marked increase in twin density.

By bridging experimental and natural observations, this research advances our understanding of deep basin and fault mechanics in carbonate rocks, offering critical insights into subsurface processes and informing sustainable resource extraction and seismic risk assessment.