Deformation mechanisms of naturally deformed rocksalt

This thesis presents an analysis of deformation and recrystallization processes in a variety of naturally deformed rocksalt. Tools used for the analysis involve simple microtectonic methods: transmitted and reflected light microscopy of gamma-irradiated thin sections and orientation measurements with EBSD. Case studies were chosen to represent different tectonic settings. Slightly deformed bedded Lower Triassic Röt rocksalt from Hengelo, The Netherlands; horizontal, though locally folded Z1 Zechstein salt from Neuhof-Ellers salt mine, Germany; highly strained Z4 Zechstein domal salt from Klodawa salt mine, Poland and highly deformed extrusive salt from Qum Kuh and Gramsar Hills (central Iran) were studied. The Hengelo and Neuhof-Ellers samples show abundant primary structures such as fluid-inclusion-outlined chevron or hopper crystals. The microstructures suggest that the sedimentary environment was ephemeral salt-pan for the Hengelo samples and perennial salt lake for the Neuhof-Ellers samples. The main deformation mechanisms are dislocation processes and solution-precipitation in the Hengelo samples, while the samples from Neuhof-Ellers deform solely by solution-precipitation creep due to its very fine grain size (~1 mm). In both set of samples, widespread evidence for grain boundary migration recrystallization (GBM) is present. The GBM swept out the primary fluid inclusions and transferred them to grain boundary fluid. The Klodawa samples show no primary microstructures, suggesting that it is completely recrystallized by process of GBM. The main deformation mechanism was dislocation creep as evidenced by the widespread presence of subgrains. Presence of static recrystallization related euhedral grains in some samples suggest that mine-wall convergence induced static recrystallization may alter the natural deformation-related microstructures. The highly deformed extrusive salt samples from Iran contain thin shear zones. In the shear zones, the deformation mechanism is solution-precipitation creep. The preserved porphyroclasts are rich in subgrain, indicating climb controlled dislocation creep in the subsurface. Orientation measurements demonstrate that the grain size reduction involves subgrain rotation and perhaps nucleation during the upward transport of the salt. Based on subgrain size piezometry the differential stress was less than 2 MPa for all the samples studied except that for the extrusive Iran samples, where the differential stress of ~3 MPa was calculated. This high stress value very likely represents the conditions during the upward transport of the salt