AAPG Middle East Region Geoscience Technology Workshop

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Relative Timing of Uplift along the Zagros Mountain Front Flexure (Kurdistan Region of Iraq): Constrained by Geomorphic Indices and Landscape Evolution Modeling


The Mountain Front Flexure marks a dominant topographic step in the frontal part of the Zagros Fold–Thrust Belt. It is characterized by numerous active anticlines atop of a basement fault. So far, little is known about the relative timing of the anticlines, about their evolution, or about how crustal deformation migrated over time. We assessed the relative landscape maturity of three along-strike anticlines (from SE to NW: Harir, Perat, and Akre) located on the hanging wall of the Mountain Front Flexure to identify the most active structures and to gain insights into the evolution of the fold–thrust belt. Landscape maturity was evaluated using geomorphic indices such as hypsometric curves, hypsometric integral, surface roughness, and surface index. Subsequently, numerical landscape evolution models were run to estimate the relative time difference between the onset of growth of the anticlines, using the present-day topography of the Harir Anticline as a base model. A stream power equation was used to introduce fluvial erosion, and a hillslope diffusion equation was applied to account for colluvial sediment transport. For different time steps of model evolution, we calculated the geomorphic indices generated from the base model. While the Akre Anticline shows deeply incised valleys and advanced erosion, the Harir and Perat anticlines display smoother surfaces and are supposedly younger than the Akre Anticline. The landscape maturity level decreases from NW to SE. A comparison of the geomorphic indices of the model output to those of the present-day topography of Perat and Akre anticlines revealed that it would take the Harir Anticline about 80–100 and 160–200 kyr to reach the maturity level of the Perat and Akre anticlines, respectively, assuming erosion under constant conditions and constant rock uplift rates along the three anticlines. Since the factors controlling geomorphology (lithology, structural setting, and climate) are similar for all three anticlines, and under the assumption of constant growth and erosion conditions, we infer that uplift of the Akre Anticline started 160–200 kyr before that of the Harir Anticline, with the Perat Anticline showing an intermediate age. A northwestward propagation of the Harir Anticline itself implies that the uplift has been independent within different segments. In the southeastern part, the shortening was probably accommodated by Safin Anticline to the south of Harir at time of evolution of Akre Anticline before it has been accommodated later by Harir Anticline. A northwestward propagation of the Harir Anticline itself implies that the uplift has been independent within different segments. Our method of estimating the relative age difference can be applied to many other anticlines in the Mountain Front Flexure region to construct a model of temporal evolution of this belt. Studies using tectonic geomorphology landscape modeling approaches at early stage exploration may provide a cost-efficient, rational analysis for structures before comprehensive investigations on the ground. Also, these studies will help understanding along-strike changes in the evolution of the structures and their segmentation that can be of potential importance in the petroleum exploration with respect to the charging of traps.