Thin-skinned tectonics in the Central Basin of the Iranian Plateau in the Semnan area, Central Iran

During continent–continent convergence of the Arabian and Eurasian plates, and after the late Eocene inversion of a back-arc rift, the Iranian Plateau underwent broad subsidence resulting in the formation of the Central Basin (Morley et al., 2009). New 2D seismic data acquired by National Iranian Oil Company (NIOC) in the NW–SW-trending arm of the Central Basin suggest that during the main stage of shortening (middle–late? Miocene to Pliocene), strain concentrations resulted in the development of the thin-skinned Kuh-e-Gachab, Kuh-e-Gugerd, Garmsar and Sorkh-e-Kuh structures. These structures are built of Oligocene–Miocene/Pliocene(?) rocks belonging to the Lower Red, Qom and Upper Red formations. Seismic data suggest that one of these structures comprises the south-verging Kuh-e-Gachab anticline, which is bounded by the N-dipping Kuh-e-Gachab thrust and cored by a complex array of thrust sheets forming a triangle zone. During the deformation process, two salt evaporate levels played a significant role as detachment horizons. The main detachment horizon was rooted within the Lower Red Formation, whereas the second detachment horizon was located along evaporites belonging to the Upper Red Formation. Variations in the thin-skinned style of deformation between the larger triangle zone in the western part of the Kuh-e-Gachab structure contrasts with less shortening in the smaller triangle zone to the east. This suggests that the change resulted from the increase of thickness of the mobile detachment horizon to the east. Contraction deformations are still active south of the Alborz Mountains, which is confirmed by GPS data and present-day seismicity.

► We interpreted thin-skinned structures in NE-trending arm of the Central Basin.
► Their development was controlled by the presence of two detachment horizons.
► They were formed during shortening from the Middle/Late Miocene likely to the Q.
► The Qom Formation have been wedged to the south.