Analysis of the development of drainage basins during active fold growth (Chenareh anticline, Zagros fold-and thrust belt, Iran)

Fold-and-thrust belts (FTBs) have widely developed in active orogenic systems. As structural shortening accumulates, thrust-related folding can increase in amplitude and length, causing progressive tectonomorphologic evolution of the FTB. I analyzed the growth of folds in the Chenareh anticline in southern Lorestan Province (Zagros FTB, Iran). I focus on tectonic geomorphological criteria for detecting the lateral growth of folding in tectonically active settings because of their relative ease and low cost. Due to the variety of drainage basins and their networks along the axis of the anticline as well as transversely across its forelimb and backlimb, the Chenareh anticline was considered suitable for applying morphometric indices. The morphometric characteristics of the 108 drainage basins in the study area were analyzed. The main drainage sinuosity (Smd), sinuosity of the anticline divide (Sd), and crescentness index (CI) parameters are greater, and the asymmetry factor (AF), hypsometric integral (HI), basin shape (Bs), drainage frequency (Df), drainage density (Dd), drainage density of 1st-order streams (Dd1), and ratio of streams of order 1 to the total number of streams (N1/N) are lower in the central zone than in the eastern and western fold plunge zones. The changes in these parameters correspond to the lateral growth of the fold from the center to the eastern and western fold noses. Structural and geomorphological observations confirm the results of quantitative geomorphological indices as reliable evidence of the propagation of lateral folds. Our evidence indicates the lateral growth of folds in the western and eastern zones of the anticline.