Structural, micro-structural and kinematic analyses of the Karmostaj salt diapir and geochronology and geochemistry of exotic blocks in Chah Banu salt diapir; southeast of the Zagros foreland folded

One of the main characteristic of the Zagros foreland fold-and-thrust belt and the Zagros foreland folded belt are wide distributions of surface extrusion from the Hormuz salt diapirs. This study examines the structure and kinematic of channel flow in the Karmostaj salt diapir in the southeastern part of the Zagros foreland folded belt. This diapir has reached the surface as a result of the channel flow mechanism and has extruded in the southern limb of the Kuh-Gach anticline which is an asymmetric décollement fold with convergence to the south. Structural and microstructural studies and quantitative finite strain (Rs) and kinematic vorticity number (Wk) analyses carried out within this salt diapir and its namakier. This was in order to investigate the structural evolution in the salt diapiric system, the characteristics and mechanism of the salt flow and the distribution of flow regimes within the salt diapir and interaction of regional tectonics and salt diaprism. The extruded salt has developed a flow foliation sub-parallel to the remnant bedding recorded by different colors, a variety of internal folds including symmetrical and asymmetrical folds and interference fold patterns, shear zones, and boudins. These structures used to analyze mechanisms and history of diapiric flow and extrusion. The micro-structures, reveal various deformation mechanisms in various parts of salt diapir. The measurements of finite strain show that Rs values in the margin of salt diapir are higher than within its namakier that is consistent with the results of structural studies. Mean kinematic vorticity number (Wm) measured in steady state deformation of diapir and namakier is Wm=0.45-0.48 ±0.13. The estimated mean finite deformation (Wm) values indicate that 67.8% pure shear and 32.2% simple shear deformation were involved; the implications which are discussed. The vorticity of flow indicates that in the early stage of growth, Poiseuille flow was the dominate mechanism, especially in the core of diapir with higher pure shear component relative to simple shear component, whilst a Couette flow at the margins of diapir is the dominate mechanism with higher simple shear component relative to pure shear component. The obtained kinematic vorticity number reflects spatial partitioning of dominantly Poiseuille flow in core and Couette flow along edges of diapir. These two mechanisms reflect a persistent flow governed by a simultaneous combination of pure shear and simple shear in a hybrid Poiseuille-Coutte Flow. The Chah Banu salt diapir in the southeastern part of the Zagros foreland folded belt is an excellent example of occurrence of the large blocks of bedded sediments, igneous rocks and low-grade metamorphic rocks within the Hormuz salt. The exotic blocks brought by salt diapirs provide an opportunity to examine the lithology, geochemical composition and age of the “basement extrusives or intrusives” of the Zagros orogenic belt, where there are no other exposure for direct study. The Chah Banu salt diapir include a wide variety of igneous rocks including gabbro, green diabase, basalt, andesite, dacite and rhyolite. Two igneous rocks give consistent of latest Ediacaran U-Pb zircon crystallization dates of 537–539 Ma. Different igneous samples obtained from Chah Banu salt diapir, although strongly altered, preserve geochemical characteristics compatible with formation in a within plate, extensional setting along the northern edge of Gondwana, adjacent to Proto-Tethyan Ocean at 539 Ma (late Ediacaran-early Fortunian). Whole-rock analyses of the samples with SiO2<60 wt.% (rhyolites) are entirely consistent with origin in a volcanic arc in an active continental margin setting suggesting crustal assimilation during Hormuz rhyolite volcanism. These rhyolites may be related to the Proto-Tethyan oceanic subduction. Due to the simultaneity of deposition thick evaporate strata and volcanism in the Hormuz series, according to the age of tuff obtained in this study, the age of deposition of the Hormuz evaporates in the rifting basins of Proto-Tethys is determined 537-538 Ma.