A geomorphic investigation of the Salinas de Oro salt diapir in the Pyrenees reveals that the ring fracture pattern related to the karstic collapse of the diapir crest may vary significantly depending on the rates of dissolution and salt flow, and the rheology of the overburden. The salt diapir has well-developed concentric faults related to salt dissolution subsidence throughout the Quaternary. Roof strata accommodate subsidence by a combination of downward sagging and brittle collapse leading to the development of a ring monocline that is broken by 5 to 20 m throw conjugated normal faults and a 40 m throw, 9.5-km-long and 200-m-wide keystone graben. The salt diapir top has >100-m-long sinkholes that coalesce to form hollows >70 m deep. Up to 3-km-long radial grabens with a 70 to 90 m vertical throw overprint concentric-ring faulting and displace Quaternary deposits demonstrating active salt flow and diapir rise. Radial faults are linked with salt-withdrawal faults of the Andia Fault Zone (AFZ). Salt flow from the AFZ into the Salinas de Oro salt diapir causes brittle gravitational extension of limestone strata leading to a sequence of grabens and Quaternary faults >10 km long and several hundred meters deep.

The Kaj-Rostam Abad, Dashtak and Doab diapirs are part of the Precambrian–Cambrian Hormuz series that are rich in igneous inclusions concentrated by dissolution of diapiric salt. They are situated in the Iran–Pakistan salt range and commonly associated with inclusions of basalt, trachyte, andesite, micro-gabbro, gypsum and anhydrite, with lesser amounts of carbonate rocks. The mineral assemblage in these inclusions developed in three stages: (I) magmatic stage (diopside, Ti-augite, kaersutite, plagioclase, apatite, biotite and opaque minerals), (II) late magmatic stage (biotite, quartz, chlorite, albite, calcite, titanite, epidote, actinolite and opaque minerals) and (III) vein mineralization (quartz, chlorite, albite, calcite, garnet, epidote, opaque minerals and actinolite). Clinopyroxene is diopside to Ti-augite. Actinolite, kaersutite, albite and pycnochlorite are constituents of the metasomatic rocks of the area. Chlorite geothermometry yielded a temperature of 330–500 °C for chlorite formation. Clinopyroxene thermobarometry ranges from 960 ≤ T ≤ 1440 °C and 1 ≤ P ≤ 10 kbar. The presence of halite-bearing fluid inclusions in hydrothermal quartz veins with homogenization temperatures between 320 and 350 °C points to strong evidence of hydrothermal events. The salinity of these fluids is 39.8–42.7 wt% NaCl. δ18O data on hydrothermal quartz veins range from 14.89 to 22.09 ‰ (SMOW), indicating that the studied samples were affected by fluids originated from sedimentary-evaporitic rocks. Meteoric water that penetrated the evaporitic rocks likely mixed with late magmatic fluids while subjected to magmatic heat, when buried to depths of several kilometres by the Phanerozoic cover sequence. Whole-rock geochemistry data for the studied rocks emphasize their alkaline to sub-alkaline affinities, in a transitional magmatic series.

3D modelling of geological structures is a key method to improve the understanding of the geological history of an area, and to serve as a drive for exploration. Geomodelling has been performed on a large 60000 km2 area of the Zagros fold-and-thrust belt of Iran, to reconcile a vast but heterogeneous dataset. Topography, geological surface data and dips, outcrop surveys, and well and seismic data were integrated into the model. The method was to construct a key surface maximizing the hard data constraints. The Oligo-Miocene Top Asmari layer was chosen, as this formation was regionally deposited before the main Zagros collision phase and because the numerous outcrops allow proper control of the bed geometry in the fold cores. Interpreted seismic data have been integrated to interpolate the surfaces at depth within the synclines. Several conceptual models of fold geometry have been applied to estimate the best way to convert seismic time signal to depth. Several deeper horizons down to Palaeozoic strata were deduced from this key horizon by applying palaeo-thickness maps. During the construction, the 3D interpolated surfaces could be reconverted to time, using a velocity model, and compared with previous seismic interpretations. This exercise obliged us to revise some early interpretations of seismic lines that were badly tied to wells. The 3D modelling therefore clearly improves regional interpretation. In addition, the 3D model is the only tool that allows drawing consistent cross-sections in areas where there are no seismic lines. Emerging Hormuz salt diapirs were added to the model. Dimensions and shapes of the individual diapirs were modelled using a statistical survey on the cropping out Hormuz structures. Modelling reliably demonstrated that the diapirs, when piercing, show a constant mushroom shape whose diameter depends on the stratigraphic depth of observation. This observation allowed us to exemplify relations between the pre-existing diapirs and the anticlines of the area, and to highlight the morphological changes from the inner onshore areas to the coastal and offshore areas. In addition, one of the surprising results of this study was the observation of the increasing diameter of the diapirs at the time of the Zagros collision and folding event, with growth strata and overhangs on the flanks of the diapirs.

The parabolic surface profiles of the Hormuz and Namakdan salt diapirs in the Persian Gulf suggest that they have been extruding with Newtonian viscous rheologies for the last 104 years. We derive velocity profiles for these diapirs, neglecting gravitational spreading and erosion/dissolution while assuming incompressible Newtonian rheology of the salt. Fitting known rates of extrusion at specific points in its elliptical cross-section, the dynamic viscosity of the salt of the Hormuz diapir is found to range between 1018 and 1021 Pa s. Approximating its sub-circular cross-section to a perfect circle, the range of viscosity of the salt of the Namakdan diapir is obtained as 1017–1021 Pa s. These calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt diapirs but are broader than those for salts with Newtonian rheology deforming at room temperatures. The salts of the Hormuz and Namakdan diapirs are expected to exhibit a broader range of grain size, which matches the limited existing data.