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The Longxian-Baoji Fault Zone (LBFZ) is the main structural link between the compressional Liupanshan Mountain in north and the extensional Weihe Basin in south, which accommodated complex deformation between the Tibetan Plateau and the Ordos Block. We determined the tectonic activity of the normal faults in the LBFZ using combined ridge and stream profiles measured from the natural landscape and simulated by a numerical model. The well-preserved geomorphic features (i.e., scarps) and steep scarp slopes show that the Guguan-Guozhen Fault (GGF) has been active during the Late Pleistocene to Holocene. The distinct decrease of scarp heights of the GGF near Badu and the low scarp and land surface slopes of ridge and stream profiles for the inferred northern extension of the GGF demonstrate that the GGF terminates near Badu and does not extend farther to the north. The Taoyuan-Guichuansi Fault is determined to be an Early-Middle Pleistocene fault, as evident from the different shapes and low scarp slopes of stream profiles. The longitudinal profiles of the Qianyang-Biaojiao Fault are characterized by two segments with different slopes, indicating that the fault may not have been active during the Quaternary. Our results show that the profile shapes, spatial pattern of scarp height, and the slopes of scarp and land surface of ridge and stream profiles are appropriate metrics of fault activity. Furthermore, we constructed the landform evolution in the LBFZ and suggest that it is closely related to the active tectonics. The change in fault activity reflects a tectonic transformation from an extensional regime to a dominantly transtensional regime. • Tectonic activity of the Longxian-Baoji Fault Zone analyzed from DEMs and modelling • Profiles and slopes of streams, interfluve ridges, fault scarps and land surfaces analyzed • Morphological differences suggest different activity and timing between different faults • Spatial-temporal fault pattern insights used to construct a landform evolution model • LBFZ topography linked to change in active tectonics from extension to transtension [ABSTRACT FROM AUTHOR]

Available data from the Qilian Shan in north-east Tibet suggested that decadal-scale erosion rates were closely correlated with local topographic gradient, but not with climatic factors. However, a climatic change to more arid condition was proposed to explain the discrepancy between short-term and long-term erosion rates. In order to re-evaluate the topographic, tectonic and climatic influences on erosion, we adopted five parameters (slope, mean local relief, historical cumulative seismic moment, runoff coefficient of variation and fault density) to study 11 drainage basins in north-east Tibet. Our results showed that terrain gradient, rock fracture density and rainstorm intensity had strong influence on erosion rates while 60-year cumulative seismic moments of historical earthquakes showed weaker correlations. There was a spatial variation in the erosional mechanisms across the basin, with detachment-limited dominance around the ridges (slope > 20°) and deposition dominant in the flat areas. The variation may lead to the discrepancy between short-term and long-term erosion rates. In general, our study supports the 'bath-tub' model for low relief intermountain basins, hence providing new insights into the landscape evolution of the Qilian Shan in northeastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]