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

Abstract

In the northern Tibetan Plateau, a series of northeast-striking faults have developed within the Xijianquan-Jiujing transtensional fault system (XJTFS), 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, unmanned aerial vehicle-derived digital topography, Google Earth imagery, and audio-magnetotelluric profiles reveal that the JBF, approximately 28 km in length, comprises four linear branches forming a negative flower structure. Displacement of landforms, such as terminal facets, terraces, small gullies, and ridges, indicates that the fault exhibits left-lateral strike-slip movement with a normal component. The vertical slip rate has been estimated at ∼0.02 mm/yr since ∼125 ka BP. Trenching research along the JBF identified four paleoseismic events, dated using optically stimulated luminescence (OSL) to approximately 20, 27–31, 34, and 76–78 ka BP. The potential seismic magnitude along the fault is estimated at M 6.3– 6.5. These findings, combined with regional geodetic data, suggest that late Quaternary deformation in the northern Tibetan Plateau has propagated into the southern Beishan Block. This deformation is inferred to be influenced by the clockwise transpressional deformation and northeastward movement of the Tashi micro-Block, located north of the Altyn Tagh Fault. The observed deformation pattern demonstrates strain partitioning and transfer between the northern Tibetan Plateau and the southern Mongolian Plateau.