Cenozoic Shortening and Propagation in the Eastern Kuqa Fold-And-Thrust Belt, South Tian Shan, NW China

In an orogen-foreland basin system, syn-orogenic sedimentation and deformation records within the foreland basin provide critical evidence for understanding uplift and erosion processes of adjacent orogenic belts. Foreland fold-and-thrust belts (FTBs) are widely developed around the Tian Shan range, Central Asia. Problem of how crustal shortening accumulates and propagates from the Tian Shan to adjacent foreland basins is essential for understanding the overall dynamics of Tian Shan. In this study, we interpreted three high-resolution seismic reflection profiles to estimate the magnitude and distribution of Cenozoic shortening across the Eastern Kuqa FTB, South Tian Shan foreland. Combined with well-dated syntectonic stratigraphy, we further evaluate the timing, rate, and migration of the deformation front of the Kuqa FTB. Our results suggest that the Kuqa FTB's total crustal shortening increases westward. The distribution of crustal shortening across secondary structural belts shows a gradual, basinward decrease, which can be explained by the telescoped mechanism. Propagation rates of the Kuqa FTB's deformation front indicate an episodic propagation of the foreland thrust wedge, with an acceleration after similar to 12 Ma. Similar episodic propagation pattern has also been observed in other foreland FTBs around the Tian Shan, but they show significant spatio-temporal variations in the propagation stages and related rates. Plain Language Summary The Tian Shan range stretches over 2,500 km from east to west and is one of the Earth's largest intracontinental orogenic belts. As the mountains grew, deformation propagated into foreland basins around the range, forming a series of fold-and-thrust belts (FTBs). To better understand the spatial distribution of crustal shortening, and basinward propagation process in foreland FTBs, we interpret and reconstruct three high-resolution seismic profiles across the Eastern Kuqa FTB, South Tian Shan. Our study indicates that the total crustal shortening of the Eastern Kuqa FTB increases westward. Within the Kuqa FTB, a telescoped distribution pattern of crustal shortening is also observed in frontal thin-skinned structures above the regional salt decollements. In addition, we find that the basinward propagation of Kuqa FTB is episodic, which is featured by a two-stage evolution pattern.