Relative timing of uplift along the Zagros Mountain Front Flexure (Kurdistan Region of Iraq): Constrained by geomorphic indices and landscape evolution modeling

摘要

The Mountain Front Flexure marks a dominant topographic step in the frontalpart of the Zagros Fold–Thrust Belt. It is characterized by numerous activeanticlines atop of a basement fault. So far, little is known about therelative activity of the anticlines, about their evolution, or about howcrustal deformation migrates over time. We assessed the relative landscapematurity of three along-strike anticlines (from SE to NW: Harir, Perat, andAkre) located on the hanging wall of the Mountain Front Flexure in theKurdistan Region of Iraq to identify the most active structures and to gaininsights into the evolution of the fold–thrust belt. Landscape maturity wasevaluated using geomorphic indices such as hypsometric curves, hypsometricintegral, surface roughness, and surface index. Subsequently, numericallandscape evolution models were run to estimate the relative time differencebetween the onset of growth of the anticlines, using the present-daytopography of the Harir Anticline as a base model. A stream power equationwas used to introduce fluvial erosion, and a hillslope diffusion equation wasapplied to account for colluvial sediment transport. For different time stepsof model evolution, we calculated the geomorphic indices generated from thebase model. While Akre Anticline shows deeply incised valleys and advancederosion, Harir and Perat anticlines have relatively smoother surfaces and aresupposedly younger than the Akre Anticline. The landscape maturity leveldecreases from NW to SE. A comparison of the geomorphic indices of the modeloutput to those of the present-day topography of Perat and Akre anticlinesrevealed that it would take the Harir Anticline about 80–100 and160–200?kyr to reach the maturity level of the Perat and Akre anticlines,respectively, assuming erosion under constant conditions and constant rockuplift rates along the three anticlines. Since the factors controllinggeomorphology (lithology, structural setting, and climate) are similar forall three anticlines, and under the assumption of constant growth and erosionconditions, we infer that uplift of the Akre Anticline started 160–200?kyrbefore that of the Harir Anticline, with the Perat Anticline showing anintermediate age. A NW-ward propagation of the Harir Anticline itself impliesthat the uplift has been independent within different segments. Our method ofestimating the relative age difference can be applied to many otheranticlines in the Mountain Front Flexure region to construct a model oftemporal evolution of this belt.