ABSTRACT
During an extensive field campaign, we have studied the full range of microstructures from the top to bottom of the salt dome and glacier Kuh-e-Namak in Iran. For the studies, the samples were gamma-irradiated, which was followed by the thin section preparation including dry polishing and etching (Schleder and Urai, 2005). Microstructures were studied under reflected and transmitted light. The salt samples are of variable impurity content and capture a sequence of microstructures that reflect the progressive recrystallization from the top part of an extrusive dome down along the slope of an adjacent glacier. The domal coarse-grained halite is typical with relicts of rectangular crystals with growth bands and elongated porphyroclasts that are surrounded by parallel zones of recrystallized halite grains. Down along the profile of the glacier, the degree of recrystallization increases, the content of porphyroclasts progressively decreases on behalf of the fine-grained matrix of elongated and strain-free halite grains. The microstructures are interpreted in terms of combined dislocation creep and solution-precipitation creep. Since pressure solution is dominant in salt glaciers at low deviatoric stress, the fine-grained salt deforms much more rapidly than predicted based on dislocation creep allowing the flow of salt glaciers as predicted by Wenkert (1979).
