Fan morphology evidence on Late Quaternary deformation in the southern front of the Central and Eastern Alborz Mountains in the Eyvanekey, Garmsar, Semnan areas, Northern Iran

Abstract

Although numerous studies have been done on the Alborz Mountains, few have examined Quaternary events based on alluvial fans which are located in front of the southern limb of the Central and Eastern Alborz Mountains. This study analyzed the morphometric indexes for 131 alluvial fans (three generations) in the Eyvanekey, Garmsar, and Semnan areas (As, WLF, Bull, Fa, Fs, Fg, Fc, R) as well as for basins (Da, AF, T, Bs), mountain fronts (Fmf, Smf, Vf, Fd), and rivers (Sl). The morphometry results show that a young deformation in this area has caused on uplift in the crust along structures in the Alborz. The Garmsar area is more active than the Semnan area in which both are more active than the Eyvanekey area. All of the alluvial fan evolution in this area relate to the Quaternary events. The study on the information obtained from the exploitation wells and geoelectric profiles of the region shows that the Alborz uplift in the north is associated with the erosion and deposition of the new deposits in the form of alluvial fans. The bedrock behavior at the base of the fans has a direct effect on the formation of the second- and third-generation fans. The effect of the continual compressional tectonics in the Late Quaternary is associated with the uplifting evaporite masses, the uplifting hanging walls of the reverse faults, and the growth of the folded structures.