Structural styles in the Zagros Simple Folded Zone, Iran

Abstract

Arabia–Eurasia convergence is achieved in the NW Zagros by a combination of shortening on NW–SE-trending folds and thrusts, mainly in the Simple Folded Zone, and by right-lateral strike-slip on the NW–SE-trending Main Recent Fault. A balanced and restored cross-section across this part of the range indicates c. 49 km of shortening. This probably occurred since c. 5 Ma, providing an estimate of the long-term shortening rate across the Simple Folded Zone of c. 10 mm a-1. The geometries of exposed structures suggest both basement thrusts and thin-skinned décollement levels, with major folds possibly nucleated above basement faults. Fold geometries indicate several décollement horizons; shale units are candidates, as well as evaporites in the Neogene, Mesozoic, Lower Palaeozoic and upper Proterozoic successions. The SE part of the Simple Folded Zone deforms by north–south shortening on broadly east–west-trending folds and thrusts. The link between these regions occurs via a set of fault blocks c. 400 km wide in total, each bounded by north–south right-lateral faults. Incremental changes in the strike of some of the folds occur across these right-lateral faults, with more east–west orientations to the east.