Control of salt tectonics on the hydrocarbon traps development: the surrounding structures of the Qom Kuh, Central Iran

Salt tectonics and salt structures are attractive targets for hydrocarbon exploration since salt-related deformation can form hydrocarbon traps and influence hydrocarbon migration. Salt diapirs are considered a suitable site for reserving natural oil/gas, landfills, and hazardous wastes. Determination of the origin and age of salt diapirs, the diapir formation and evolution model, and their impacts on the surrounding structures are very necessary for hydrocarbon exploration. To characterize the structural and tectono-sedimentary evolution of the salt diapir at the Qom Kuh, located in the Qom basin (Central Iran), this research describes the origin, timing, and evolution history of the salt structure through the tectono-sedimentary analysis and field study. Moreover, the effect of salt diapirism on the surrounding structures is investigated in the study area. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth salt structure indicate that the salt extrusion occurred during two stages in the Qom Kuh. According to the structural evidence (e.g., hook and cusp) and the tectonic-sedimentary analysis, the first stage of salt extrusion happened in the Early Miocene concurrently with the extensional deformation event from the Eocene to the Early Miocene in the study area. The second stage of salt diapirism and its extrusion occurred during multi-stages of the Zagros orogenic compression from the Late Miocene to the present day. The final geometry of the salt diapir at the Qom Kuh formed along a releasing bend that was created by dextral transpressional strike-slip fault activity during the Zagros orogeny. Based on the lower thickness of evaporite units in the Upper Red Formation (Early Miocene) compared to the Lower Red Formation (Early Oligocene) and observing fragments of the Eocene volcanic rocks in the extruded salt on the ground surface, the Lower Red Formation salt along with the Upper Red Formation evaporites considered as the main source of salt diapirism in the Qom Kuh. Salt diapirism affected the surrounding structures of the Qom Kuh such as the Western Kuh-e-Namak and Western Alborz anticlines. The fold geometry and the hydrocarbon trap development in the Western Kuh-e-Namak and Western Alborz fields are controlled by salt tectonics and the occurrence of inversion tectonics. The results of this study could add data to worldwide examples of the impact of salt tectonics on the hydrocarbon trap development in collisional orogenic belts.

Keywords: Salt tectonics; Tectono-sedimentary analysis; Hydrocarbon traps; Qom Kuh; Central Iran