<p>The eastern Zagros Fold and Thrust Belt (ZFTB) in Iran includes a salt tectonic province with roughly 130 salt-gypsum diapirs emerging within the Neoproterozoic-Early Cambrian Hormuz Complex. The diapirs in the ZFTB differ in composition and in their distribution of exposed caprock m&#233;langes (CRMs). Although there are numerous studies focused on the geochronology and geochemistry of igneous rocks as exotic blocks associated with CRMs, the geochemistry, and petrography of carbonates remain to be systematically investigated. The Paskhand Diapir is a unique little diapir with no visible salt rock at the surface. Its CRMs consist of massive and layered gypsum, carbonate, marlstone, and siltstone,&#160; which are associated with diabase exotic blocks. The carbonate paragenesis is being examined. A grey fine crystalline&#160; dolomite is considered to have originated early during diagenesis from a Neoproterozoic marine environment. Other carbonates can be distinguished on the basis of their microspar, and spar cements. In general, the major minerals are dolomite and calcite, with quartz and iron oxides being in minor abundance. Important trace minerals are pyrite, sphalerite, talc, mica, K-feldspar, malachite, bassanite, rutile, chlorite, and apatite. Their abundance in mineral assemblages is variable, also depending on the locality within the diapir. Later-stage calcitic veins frequently cross-cut through micritic and microspar cemented lithologies. Lithological mapping shows that the edge of the diapir commonly exhibits a greater variety of mineralization modes with extensive recrystallization as compared with its core. The <em>&#948;</em>13C values of dolomite range from &#8211;7.0 to +2.7 &#8240; V-PDB. This range indicates that seawater was the principal source of reactants for dolomite precipitation, although with some inorganic carbon derived from organic matter oxidation. The <em>&#948;</em>18O values of dolomite range from &#8211;0.55 to &#8211;13.13&#8240; V-PDB, reflecting a temperature fractionation effect. The carbonate formation temperatures of the Hormuz complex (both veins and host rock) were determined for the first time by using the &#916;47 (paleo)thermometer in dolomite. &#916;47 values range between 0.422 &#177; 0.015 and 0.287 &#177; 0.015 &#8240;, indicating diagenetic closure temperatures of between 116.4 &#177; 11.7 and 271.2 &#177; 32.5&#160; &#186;C. An intensive interaction of hydrothermal fluids with the host rock during localized carbonate recrystallization is thus evidenced.</p> <p>These results show that a correct interpretation of the mechanism(s) of carbonate alteration is critical for reconstructing the history of diapirism in the area. We hypothesize that carbonates in CRMs were reworked through a series of events largely influenced by thermochemical sulfate reduction (TSR) at T &#8805; 110 &#186;C.&#160;</p> <p>&#160;</p> <p>&#160;</p>
<p>Growth rate of salt diapirs usually oscillates depending on several factors. The growth can be arrested by depletion of the source layer or diapir burial, conversely, diapir reactivation occurs through erosion of the overburden and/or introduction of tectonic forces. Examples of reactivated diapirs can be observed in the Zagros Mountains in Iran. There, tectonic shortening responsible for development of the Zagros Fold and Thrust Belt simultaneously squeezes the diapirs, which extrude salt onto the surface. The top section of the diapir is usually affected by meteoric water, which dissolves the salt and leaves behind insoluble material embedded within the source layer, forming the so called caprock. This caprock can be assumed to be already present before the reactivation of the diapirs during shortening, hence it may play a role in the development of the salt extrusions. Geometry, composition and mechanical properties of the caprock can vary widely depending on factors such as original composition of diapiric material, dissolution and growth rates, etc. Additionally, exact mechanical properties of any caprock are difficult to determine and are currently largely unknown.&#160;</p> <p>Hence, we present a series of 2D numerical simulations utilising finite element method to investigate how different geometries and rheologies of the caprock affect the shape of the subaerial extrusions. The analysis was performed with three variable parameters (caprock viscosity, cohesion, and thickness) for three scenarios of diapirism (1 - purely shortening-based, with depleted source layer; 2 - purely buoyancy-based, with preserved source layer and no tectonic forces, and; 3) a combined scenario). We analysed the general deformation patterns as well as quantifiers such as velocities, displacements, strains, strain rates and ratios between vertical and horizontal components of the quantifiers. We investigated variability of averaged values of the quantifiers in time as well as detailed spatial distribution for the finite state of simulation.&#160;</p> <p>The simulations revealed the strong contrast between less (low cohesion and viscosity) and more competent rheologies in term of deformation patterns. The former tends to result in caprock material being thinly spread over the surface of the salt extrusion, whereas in the latter case the caprock fractures into &#8220;rafts&#8221; floating on top of the extrusion. The exact geometry of the rafts (size, spacing, distribution) is highly dependent on the geometry and type of diapirism. We also compare the resultant patterns to the quantifiers, especially velocities and their ratios, establishing clear ties between the patterns and deformation dynamics.&#160;</p>
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