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Studies have shown that the growth of the Qilian Shan, the northeastern margin of the Tibetan Plateau, started ~10 Ma ago. However, when and how it expanded northwards is still under debate. Here we focus on the rock uplift pattern of the Yumu Shan, an active fault-related fold in the Hexi Corridor north to the Qilian Shan. Normalized channel steepness achieved from the analysis of river longitudinal profiles shows a spatially variant rock uplift pattern, with higher rates in the middle part and lower rates towards the west and east tips. The compression of the mountain is typically accommodated by fault-fold related shortening and vertical thickening. Apatite fission track thermochronology reveals that the growth of the Yumu Shan started ~4 Ma ago, similar to the work on active tectonics. Combining the onset ages of the growth of the Qilian Shan (10 Ma), Laojunmiao anticline (3–4 Ma), Baiyanghe anticline (3–4 Ma), Wenshu Shan (4.5 Ma) and Heli Shan (2 Ma), we draw an conclusion that the NE margin of the Tibetan Plateau initiated growth in the mid-Miocene and expanded to the Hexi Corridor and to the south of the Alxa block in the early Pleistocene. [ABSTRACT FROM AUTHOR]

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]