Mingxin Tao

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 .

We use field investigations, topographic profiles, and 10 Be exposure dating to constrain the growth rate of the Yumu Shan, a thrust‐bounded mountain range at the northeastern margin of Tibet. Wind gaps, fault scarps at the mountain front, and hanging paleocatchments indicate that the Yumu Shan is growing both laterally and vertically. Scarp profiles and 10 Be ages yield rock uplift rates of ∼500 and ∼800 mm ka −1 for the eastern and central parts of the range, respectively. The fact that the rock uplift rate in the high center of the Yumu Shan exceeds catchment‐wide 10 Be denudation rates, which range from ∼180 to ∼280 mm ka −1 , indicates that the mountain range continues to rise and has not yet reached a topographic steady state. Combining the total structural relief of the range with the rates of rock uplift and denudation suggests that the growth of the Yumu Shan started 3.7 ± 0.9 Ma ago.

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.