Oblique Thrust of the Maidan Fault and Late Quaternary Tectonic Deformation in the Southwestern Tian Shan, Northwestern China

Abstract The Maidan fault, which is an east‐northeast trending fault in the southwestern Tian Shan, is a sinistral reverse fault that extends more than 400 km in length and constitutes the boundary between the southwestern Tian Shan and the Tarim Basin. Here we quantify its late Quaternary activity based on the interpretations of high‐resolution remote sensing images and detailed field investigations. In the Aheqi valley, an ~150‐km‐long active fault can be divided into northeastern and southwestern segments based on variations in its strike and geometry. Based on the analysis of its offset geomorphological features and the dating of Quaternary sediments, we estimate the late Quaternary shortening rate across the fault to be 1.19 ± 0.25 mm/year, the sinistral strike‐slip rate to be 1.56 ± 0.64 mm/year, and the oblique thrust rate to be 1.96 ± 0.69 mm/year. Active tectonics, GPS crustal deformation data, and seismic activity indicate that the deformation in the southwestern Tian Shan is characterized by out‐of‐sequence thrust faulting and folding. Late Quaternary deformation has been partitioned into low‐angle thrust faulting along the Kalpin Tagh foreland fold and thrust system and sinistral reverse faulting along the high‐angle range‐front Maidan fault. The sinistral Maidan fault acts as a nucleation point for slip partitioning system, which can be viewed as positive flower structure with its surrounding thrust faults.