Dynamic and static recrystallization-related microstructures in halite samples from the Klodawa salt wall (central Poland) as revealed by gamma-irradiation

Abstract

Microstructures of 33 rocksalt specimens from gallery walls from the highly strained part of the K odawa Salt Structure (Poland) were analyzed in gamma-irradiated and etched thin sections in reflected and transmitted light. Two types of microstructures could be distinguished i) dynamic recrystallization related ones caused by natural deformation and ii) static recrystallization related ones with uncertain origin, perhaps caused by subsequent mine-wall convergence. Natural deformation-related microstructural features are the abundant subgrains and strain-free regions at grain boundaries together with elongated subgrains which imply dislocation climb controlled creep accompanied with fluid-assisted grain boundary migration as the deformation mechanism. Using subgrain size piezometry, differential stresses between 0.9 to 3.1 MPa were calculated. All the samples contain a few percent (< 5 %) of euhedral statically recrystallized phase. In three samples the euhedral, statically recrystallized grains may comprise up to 85 % of the material. The microstructure suggests that the static recrystallization post-date the natural deformation-related features. The static recrystallization is thought to be due to mine-wall convergence. The pervasive crack system in the samples may also be explained by the stress concentration and subsequent minor mine-wall convergence. Detailed observations of the mutual relationship between the microcracks and the euhedral, statically recrystallized phase imply that as the new grains have grown, and