Landscape response to deformation in the Sabalan area, NW Iran: Inferred from quantitative morphological and structural analysis

Abstract

ABSTRACT The geological and tectonic background of the Sabalan area in NW Iran and its present-day surface processes make it ideal for examining the effects of tectonic processes in shaping the Earth's crust. As a result of the intense distribution of pre-Quaternary and Quaternary structures (e.g., faults, joints and folds), most of the drainage basins in the southern and central parts of the study area have developed under tectonic-dominated conditions, whereas the effects of erosional processes are greater in the north and east. An evaluation of the geomorphic indices using the index of active tectonics (IAT) and analytical hierarchy process (AHP) methods shows that the AHP results are more reliable than the IAT results and are coherent with the geological and structural conditions of the study area. The geomorphic results are highly consistent with the intensity and distribution of fractures. The majority of fractures have developed in a NW–SE direction, indicating antithetic R′ Riedel fractures to the main NE-SW-trending faults. However, a significant number of the fractures in the study area are NNE–SSW- and NE–SW-oriented R and P fractures and NNW–SSE-oriented tension fractures. Palaeostress analysis of the fault data shows at least two faulting events in the pre-Quaternary and Quaternary, respectively. The pre-Quaternary NNW–SSE-striking dextral strike-slip faults experienced post-Eocene 25–30° clockwise rotation and re-activated as NE–SW-striking sinistral faults during the Quaternary. Although seismic activity is currently low, the consistency of our results with the regional stress data show that the study area is still tectonically active.