Fluvial styles during fold growth: An example from the eastern segment of the Qiulitage and Yakeng folds, southern Tian Shan, China

Geomorphological evidence provides significant information on the processes that govern lateral propagation of a growing active anticline. Within actively developing fold-and-thrust belts evidence can be recorded in Quaternary landforms and the drainage network. In the Kuqa fold-and-thrust belt (KFTB), located in the southern foothills of the Tian Shan mountains, we investigate the topographic and fluvial geomorphic records of the eastern part of the Qiulitage and of the Yakeng anticlines. In this study, using a morphometric approach, including the analysis of anomalies in the spatial patterns of river channels, topographic profiles along anticline crests, and the geometry of wind gaps, we speculate on the lateral propagation of these folds. We extract the drainage network related to the growth of the Yakeng and Qiulitage folds from the beginning onset of the folding (5.5 Ma ago) to its acceleration in the Late Quaternary. We examine 15 rivers and their catchments crossing the eastern segment of Qiulitage and the Yakeng anticlines. Our results demonstrate how the ridges along the eastern segment of Qiulitage and Yakeng folds feature (1) an anticline ridge with decreasing relief from the topographic crest to the plunging ends of the ridges, (2) alternating wind gaps and water gaps from west to east, (3) a drainage system closely controlled by folding and differential uplift, (4) a decrease in drainage basin maturity towards the east only, and (5) fluvial features that provide age constraints. We then document the evolution of the drainage network and provide insights on the growth history of the eastern Kuqa fold-and-thrust belt from its nucleation to its growth acceleration. The connections between the topography and the drainage allow us to present an integrated model that could explain their lateral and vertical fold growth along the two folds along their leading edges.