Fold Growth and Lateral Propagation Across the Xihu Anticline Documented by Fluvial Terraces in the Northern Chinese Tian Shan Foreland

Fluvial geomorphology is of primary importance for characterizing recent growth of a thrust-related anticline in a foreland setting. This work focused on growth and lateral propagation of the Xihu anticline, an outermost structure in the northern Chinese Tian Shan foreland. The topography along the crest of the Xihu anticline displays a clear, asymmetrical bow shape with the structural apex close to its eastern end, implying a higher rate of westward propagation. The further evidence is from the observations on alluvial sequence developed over the anticline. By combination of ¹⁰Be depth profile exposure dating and optically stimulated luminescence dating methods, the abandonment age of the highest geomorphic surface at the structural apex and the middle segment of the Xihu anticline was determined to ∼173 and ∼50 ka, respectively. Much younger abandonment ages near the western and eastern ends of the anticline were constrained to ∼11 and ∼22 ka, respectively. Together with the results of topographic analyses, the westward and eastward propagation rates of the Xihu anticline were determined to ∼340 and ∼39 mm/yr, respectively. Correspondingly, the shortening rates at four investigated sites were estimated to ∼0.46 mm/yr (near the western end), ∼0.76 mm/yr (along the middle segment), ∼0.81 mm/yr (at the structural apex), and ∼0.52 mm/yr (near the eastern end), respectively. Our results reveal the nature of the diachroneity of alluvial features developed over a growing fold in a foreland setting, which is vital for understanding the responses of fluvial processes to fold growth.