Tectonic and fluvial geomorphology of the Zagros fold-and-thrust belt

Abstract

Abstract

The Zagros-fold-and thrust belt has been selected to explore landscape responses to tectonic and climatic drivers using river profile steepness (ksn), relief from topography, and basin scale Hypsometric Index (HI) extracted from Shuttle Radar Topography Mission (SRTM) 30 m dataset. There are differences in the ksn and the HI value from one area to another across the Zagros range. The northeastward presence of high HI values with respect to the seismicity cut-off in the combined Dezful/Bakhtyari region is attributed to wetter conditions, in turn driven by high strain and high topographic gradients in the Bakhtyari region. Drier climate and low power rivers in the Fars region promote plateau growth, and high HI values occur south of the thrust seismicity cut-off. In spite of the regional differences in ksn and HI, there is a similarity in the integrated relief along swath profiles, consistent with the similar rate of strain and total strain across different parts of the Zagros.
Digital Elevation Model (DEM)-based geomorphic indices; Hypsometric Index (HI), Surface Roughness (SR) and their combination Surface Index (SI) have been applied to quantify landscape maturity in the Kirkuk Embayment of the Zagros. Landscape maturity suggests out of sequence deformation towards the hinterland in opposite sense to classical ‘piggyback’ thrusting model. The SI shows new previously undiscovered anticlines of hydrocarbon potential. New balanced cross-section indicates shortening in the order of ~5% in the Zagros foreland.
Basin-scale values of HI exhibit sharp boundary of the low/high HI transition in the south of the Himalaya consistent with the zone of the Main Himalayan Thrust (MHT), and indicate the controls of the MHT on Himalayan topography. Smaller magnitude increases in HI value across the physiographic transition (PT2) do not support the out-of-sequence model of active deformation of Himalayan tectonics.
Point-counting technique was conducted for modern river sand from the Zagros suture and the Neogene sandstones of the Zagros foreland. Results show recycled orogen provenance and litharenite composition and spatial increase in quartz content towards the northwest, which might refer to provenance change and/or drainage reorganization. The more lithic composition of river sand and the Neogene sandstone refers to an uplift of the Zagros suture area, which is partly caused by the out-of sequence deformation of the Mountain Front Fault.