Chlorine isotopes unravel conditions of formation of the Neoproterozoic rock salts from the Salt Range Formation, Pakistan

During the late Neoproterozoic, the Salt Range in Pakistan was one of the regions where the Tethys truncated and marine strata developed. The numerous transgressions and regressions that occurred during that period provided enough initial material for the development of marine evaporites. The geology of the Salt Range is characterized by the presence of dense salt layers and the existence of four regional and local scale unconformities. These thick salt deposits geologically favor potash formation. Here we coupled chloride isotope geochemistry and classical chemistry of local halite samples to assess the extent of brine evaporation that ultimately formed the salt deposits. Our results indicate that evaporites in the Salt Range area are Br-rich and precipitated from seawater under arid climate conditions. The corresponding δ37Cl values vary from –1.04‰ to 1.07‰, with an average of –0.25‰ ± 0.52‰, consistent with the isotope range values reported for other evaporites worldwide. The positive δ37Cl values we obtained indicate the addition of nonmarine Cl, possibly from reworking of older evaporites, the influx of dilute seawater, the mixing of meteoric and seawater, and the influence of gypsum-dehydration water. The negative Cl isotope compositions (δ37Cl < –1‰) indicate that brines reached the last stages of salt deposition during the late Neoproterozoic. We conclude that the Salt Range Formation could be promising for K-Mg salts.

Chemical-mechanical-hydraulic coupling in deforming, dehydrating halite-gypsum rocks - implications for basal detachments in thin-skinned tectonics

&lt;p&gt;Long-distance transport along weak basal detachments in thin-skinned tectonics is often accomplished by rheologically weak evaporites. This weakness can be attributed to&amp;#160; the behavior of gypsum and/or halite. While the former dehydrates and the released fluid reduces the effective stress in the system, the latter is known to be extremely weak at the corresponding conditions. Separately, both minerals and their behavior under tectonic loading have been studied in great detail. However, these studies on single minerals are limited in that natural detachments are often not monomineralic and are clearly affected by interdependencies between different mineral species. In evaporitic sequences, two key couplings that can be expected are: 1) the sensitivity of the dehydration reaction to the pore fluid pressure versus the notoriously low permeability of rock salt (a potentially negative feedback), and 2) the exposure of halite to undersaturated water released from the gypsum dehydration reaction, versus the response of the dehydration reaction to lower water activity due to dissolved salt species (a potentially positive feedback).&amp;#160;&lt;/p&gt;&lt;p&gt;Here we present insights from experiments that used time-resolved (4D) synchrotron tomographic microscopy and our x-ray transparent triaxial deformation rig Mj&amp;#248;lnir to document the evolution of layered gypsum-halite samples that were simultaneously deformed and dehydrated. Our data, which were acquired at the TOMCAT beamline at the Swiss Light Source, allow us to visualise chemical-hydraulic-mechanical feedbacks on the grain scale, and quantify the microscale evolution of transport properties. In this contribution, we show that gypsum dehydration affects the capacity of the halite layers to retain the liberated fluids. The reaction itself generates the pore fluid pressure to create permeability in the salt layers through hydraulic fracturing. Dissolved salt significantly accelerates the reaction, and the evolving interconnected porosity facilitates the transport and precipitation of solutes, which contributes to the rheological complexity. These insights have, potentially significant, repercussions on the long-standing assumption about the significance of the gypsum dehydration on thrust fault formation within evaporitic sequences.&lt;/p&gt;

EFFECT OF GYPSUM ADDITIVE ON QUALITY OF COMPOSITIONAL BINDING MATERIALS CELLULAR STRUCTURE

The effect of gypsum additives on the process of lime slaking and the quality of the composite binder is discussed. It is established that a different water-solid ratio, the water temperature and the use of an additive of natural gypsum can regulate the rate of the lime slaking process. The effect of this additive on the kinetics of the process, the temperature factor, the dispersion of the product and the quality of the products obtained by slaking are considered. During the hydration of highly active lime, the slaking temperature reaches high values, at which the process of gypsum dehydration begins. The combination of the exothermic process of lime slaking and the formation of a medium of saturated water vapor with the addition of natural gypsum to lime forms the semi-aquatic gypsum СаSО4∙0,5Н2О. It does not dehydrate, does not become insoluble and retains its chemical properties. There is no exothermic effect of crystallization of anhydrite. Strength results of composite binder cellular structure demonstrate that lime-based binder samples with the addition of natural gypsum under autoclave conditions are more solid than binder-free samples.

Study of Gypsum Dehydration Time in CaCl2 Solution

The preparation of the alpha form of calcium sulphate hemihydrate is technically relatively complicated. The idea is to allow 1.5 molecules of water contained in gypsum to leave through dehydration in liquid form. This can only be achieved under hydrothermal conditions, namely in an autoclave or by increasing the boiling point of the solution in which the gypsum is located during dehydration. The paper deals with the dehydration of gypsum in a calcium chloride solution. The influence of the concentration and temperature of the selected solution on the dehydration time of the gypsum was monitored.