Neotectonic features of Gotvand - Lali region, southwest Iran

The morphology of the Earth is a result of interactions between climate, tectonics, and geology and the investigation of neotectonics is one of the vital disciplines in Earth science, because the results of regional studies of active tectonics are significant for evaluating natural hazards as well as land use development and management in populated areas. In this regard neotectonic features of Gotvand – Lali region is investigated here. The study area is part of Dezful embayment in the Zagros Fold Belt composing mostly of Neogene formations and Quaternary deposits. The area is an economically important region regarding its location at the mountain - plain boundary involving three oil fields namely Papileh, Zilaie and Lali fields and the Upper Gotvand dam and reservoir as the highest rock fill dam in Iran. The location of the study area in the Zagros Active Belt as the most active seismotectonic zone of the country is another prominent feature of this region. The region is characterized by well-known active faults say Lahbari and Pir-Ahmad thrust faults, a newly introduced tectonic lineament named as Lali-Ahvaz trend and extensive outcrop of highly mobile evaporitic Gachsaran Formation of Miocene Age. A unique exposure of salt piercement in the Upper Gotvand dam reservoir known as Ambal salt pillow or ridge is of prior importance as well. Neotectonic movements that affected the region are manifested as faulting and folding, deflection of the river courses, rough topography, straight river courses and fault scarps. Assessment of fault trends, fracture system and drainage network in the study area based on field survey and satellite imagery shows a reasonable relationship between fracture system and drainage pattern distribution as a key morphological element. Morphotectonic indices indicate that the regional tectonic activity is high and there is a fairly relation between the fault occurrence and fracturing. The whole region is affected by N-S trending Lali-Ahvaz basement lineament that is evident from the rotation of surface and subsurface structures in the region and river and drainage alignments. This emphasizes the contribution of pre-existing