Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration

Full-field numerical modeling is a useful method to gain understanding of rock salt deformation at multiple scales, but it is quite challenging due to the anisotropic and complex plastic behavior of halite, together with dynamic recrystallization processes. This contribution presents novel results of full-field numerical simulations of coupled dislocation glide and dynamic recrystallization of halite polycrystalline aggregates during simple shear deformation, including both subgrain rotation and grain boundary migration (GBM) recrystallization. The results demonstrate that the numerical approach successfully replicates the evolution of pure halite microstructures from laboratory torsion deformation experiments at 100-300 degrees C. Temperature determines the competition between (a) grain size reduction controlled by dislocation glide and subgrain rotation recrystallization (at low temperature) and (b) grain growth associated with GBM (at higher temperature), while the resulting crystallographic preferred orientations are similar for all cases. The relationship between subgrain misorientation and strain follows a power law relationship with a universal exponent of 2/3 at low strain. However, dynamic recrystallization causes a progressive deviation from this relationship when strain increases, as revealed by the skewness of the subgrain misorientation distribution. A systematic investigation of the subgrain misorientation evolution shows that strain or temperature prediction from microstructures requires careful calibration. Rock salt, which is dominantly composed of halite, has unique physical properties and plays a key role controlling the evolution of sedimentary basins and mountain chains. Such rocks are also important in petroleum systems, and are used for the geological storage of Geo-Energy products. However, understanding rock salt behavior is challenging because multiple deformation and recrystallization processes often operate simultaneously when halite is subjected to stress. This contribution presents microdynamic numerical simulations that replicate the main processes that take place during halite deformation at different temperatures. These include glide of dislocations, which are crystallographic defects, and temperature-controlled recrystallization processes including rotation of subgrains, nucleation of new grains, and migration of existing grain boundaries. The simulations are compared with laboratory experiments, and successfully reproduce them. Subgrain rotation is active at low temperatures, leading to the splitting of grains into smaller ones. As temperature increases, grain boundaries become mobile and grains grow to reduce the energy produced by dislocation glide. Although these processes strongly influence the resulting microstructure, the crystallographic axes are oriented similarly in all cases. We discuss how the effects of multiple microdynamic processes can be evaluated together to accurately estimate strain and the deformation conditions of rock salt. The temperature-dependent transition from subgrain rotation to grain boundary migration (GBM) is simulated, reproducing torsion experimentsIsotropic GBM changes grain size and shape but only slightly affects crystallographic preferred orientationThe relationship between subgrain misorientation and strain is influenced by dynamic recrystallization and thus by temperature

Automated summary

This study presents novel results of full-field numerical simulations of rock salt deformation, specifically the behavior of halite during simple shear deformation. The study successfully replicates laboratory experiments and reveals the competition between grain size reduction and grain growth, controlled by dislocation glide and subgrain rotation recrystallization versus grain boundary migration. The relationship between subgrain misorientation and strain deviates from a power law relationship with increasing strain, indicating the influence of dynamic recrystallization. Understanding rock salt behavior is important for various geological applications, and these findings contribute to accurate estimation of strain and deformation conditions.