Late Quaternary tectonics of the Jiujing-Bantan fault along the southern Beishan Block and its implication for the northward growth of the Tibetan Plateau

In the northern Tibetan Plateau, a series of northeast-striking faults developed within the Xijianquan-Jiujing Transtensional Fault Group (XJTFG), located approximately 150 km north of the Altyn Tagh fault along the southern Beishan Block. Among these, the easternmost Jiujing-Bantan fault (JBF) is the most active. Field mapping data, unmanned aerial vehicle-derived digital topography, Google Earth images, and audio-magnetotelluric profiles along the JBF reveal that this fault, approximately 28 km long, consists of four linear branches forming a negative flower structure. The offset of various landforms (such as terminal facets, terraces, small gullies, and ridges) suggests that the JBF is characterized by left-lateral strike-slip movement with a normal component. The vertical slip rate has been approximately ~0.02 mm/yr since 125 ka BP. Excavated trenches identified four paleoseismic events, which were dated using the optically stimulated luminescence method to ~20, 27-31, 34, and 76-78 ka BP. Estimation of the potential seismicity magnitude along the JBF is 6.3-6.5. These findings, combined with regional geodetic patterns, suggest that Late Quaternary deformation in the northern Tibetan Plateau has extended into the southern Beishan Block. It is inferred that the Late Quaternary tectonics of the JBF were influenced by clockwise transpressional and northeastward movement of the Tashi Block towards the north of the Altyn Tagh fault. This deformation pattern demonstrates strain partitioning and transfer between the northern Tibetan Plateau and the southern Mongolian Plateau.