REGIONAL VARIABILITY AMONG FLEXURAL MODELS FOR THE ZAGROS FOLD-THRUST BELT AND FORELAND BASIN, IRAQ AND IRAN

The Zagros fold-thrust belt formed during the Cenozoic Arabia-Eurasia collision and persists for ~2000 km, from SW Iran across Iraqi Kurdistan to SE Turkey. The associated peripheral foreland basin parallels the Zagros crustal load and thickens along strike to ~12 km depocenters in the Kirkuk and Dezful embayments. Differential advance of the deformation front (or Mountain Front Flexure) into the Zagros foreland basin is characterized by alternating salients (Fars and Lorestan) and intervening re-entrants (Dezful and Kirkuk). This study investigates potential controls on this characteristic along-strike architecture of the Zagros fold-thrust belt and the effect of flexural variations on the geometry of the Zagros foreland basin. To determine what controls the present-day flexural configuration of the Zagros basin, six schematic cross-sections were generated. The regional cross-sections are based on DEM topography integrated with six structural profiles depicting structural relationships among various tectonostratigraphic units. The Zagros tectonostratigraphic divisions are based on major tectonic events: identified surfaces for the top Paleozoic, top Triassic, top Jurassic, top Lower Cretaceous, top Upper Cretaceous, and top Eocene represent the onset of rifting, passive margin, ophiolite obduction, flexural subsidence, and Zagros orogeny, respectively. Using OSXFlex2D flexural modeling software, we generated predictive flexural profiles as a function of the density and thickness of the thrust-sheet loads as well as sediment loads. By a trial and error approach, we find the most appropriate flexural profiles in comparison to the observed foreland basin geometries. This allows deduction of various parameters such as flexural rigidity, vertical deflection, and lithospheric strength values (Young’s modulus and elastic thickness). The results help delimit the lithosphere properties of the Kirkuk and Dezful embayments in comparison to the Fars and Lorestan arcs and the extent of along-strike variations in key parameters. Combining these geodynamic results with the possible effects of multiple detachment layers and basement faults on the deformation front (Mountain Front Flexure) will clarify the interplay between fold-thrust belt evolution and foreland basin sedimentation.