Abstract A fault scaling law suggests that, over eight orders of magnitude, fault length L is linearly related to maximum displacement D . Individual faults may therefore retain a constant ratio of D / L as they grow. If erosion is minor compared with tectonic uplift, the length and along‐strike relief of young mountain ranges should thus reflect fault growth. Topographic profiles along the crests of mountain ranges in the actively deforming foreland of north‐east Tibet exhibit a characteristic shape with maximum height near their centre and decreasing elevation toward the tips. We interpret the along‐strike relief of these ranges to reflect the slip distribution on high‐angle reverse faults. A geometric model illustrates that the lateral propagation rate of such mountain ranges may be deciphered if their length‐to‐height ratio has remained constant. As an application of the model, we reconstruct the growth of the Heli Shan using a long‐term uplift rate of ∼1.3 mm yr −1 derived from 21 Ne and 10 Be exposure dating.
We document late Pleistocene–Holocene aggradation and incision processes at the mountain front of the Qilian Shan, an active intracontinental fold‐and‐thrust belt accommodating a significant portion of the India‐Asia convergence. The Shiyou River cuts through a NNE vergent fault propagation fold with Miocene red beds in the core and Pliocene–Quaternary growth strata on the northern forelimb. South of the anticline, Miocene strata dip 20° SSW, suggesting a similar orientation for the basal décollement. After aggradation of an ∼150‐m‐thick, late Pleistocene valley fill, the Shiyou River formed three terraces. The highest terrace, located 170 m above the river, constitutes the top of the fill. The other terraces are fill cut terraces: their treads are located 130–105 m and 37 m above the river, respectively. The 10 Be exposure dating of the terraces suggests that river incision accelerated from 0.8 ± 0.2 mm yr −1 to ∼10 mm yr −1 at 10–15 kyr. We interpret fast Holocene river incision as largely unrelated to tectonic forcing. The late Pleistocene incision rate of 0.8 ± 0.2 mm yr −1 places an upper limit of 2.2 ± 0.5 mm yr −1 on the horizontal shortening rate, assuming that incision is solely caused by rock uplift above a décollement dipping 20°. However, the actual shortening rate may lie between ∼2.2 mm yr −1 and zero because deformation of the terraces and the valley fill cannot be unequivocally demonstrated. Our estimate is consistent with the bulk shortening rate of ∼5–10 mm yr −1 across several faults in NE Tibet derived from neotectonic and GPS data, although in case of the Shiyou River, Holocene deformation is barely discernible owing to intense climate‐induced river incision.
We derive a slip rate for a thrust at the central Qilian Shan mountain front by combining structural investigations, satellite imagery, topographic profiling, luminescence dating, and 10 Be exposure dating. The seismically active Zhangye thrust transects late Pleistocene alluvial fan deposits and forms a prominent north facing scarp. The fault consists of two segments that differ in orientation, scarp height, and age. A series of loess‐covered terraces records the uplift history of the western thrust segment. Loess accumulation on all terraces started at 8.5 ± 1.5 kyr and postdates terrace formation. Gravels from the highest terrace yielded a 10 Be exposure age of 90 ± 11 kyr, which dates the onset of faulting. With a displacement of 55–60 m derived from fault scarp profiles, this yields a vertical slip rate of 0.64 ± 0.08 mm yr −1 . Along the eastern thrust segment, three 10 Be ages from the uplifted alluvial fan constrain that faulting started at ∼31 ± 5 kyr. Together with a displacement of 25–30 m this leads to a vertical faulting rate of 0.88 ± 0.16 mm yr −1 . A dip estimate of 40° to 60° for the fault plane combined with lower and upper limits of ∼0.6 and ∼0.9 mm yr −1 for the vertical slip rate gives minimum and maximum horizontal shortening rates of 0.4 and 1.1 mm yr −1 across the Zhangye thrust. Our results are consistent with geologic and GPS constraints, which suggest that NNE directed shortening across the northeastern Tibetan Plateau is distributed on several active faults with a total shortening rate of 4 to 10 mm yr −1 .
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