The late Quaternary mountain-front terrace sequences along the Langshan Mountains: Implications for the evolution of the western Hetao Graben

Abstract

As the extensional boundary between Langshan Mountains and the Hetao Basin, the vertical displacement of the Langshan Piedmont Fault (LPF) forms the typical basin and range landform and controls the uplift of the Langshan Mountains and the deposition of the Hetao Basin. Based on the 10Be concentrations for the quartz gravel samples collected from two different mountain-front terrace sequences, we can calculate that the exposure ages for T3, T2 and T1 terraces on the northern site of the LPF (Site 1) are ~136 ka, ~72 ka and ~29ka, and the exposure ages for T3, T2 and T1 terraces on the southern site of the LPF (Site 2) are ~96 ka, ~65 ka and ~45 ka, respectively. Furthermore, the vertical slip rates are ~0.33 mm/a since about late Pleistocene, ~0.21 mm/a since ~72 ka, ~0.17 mm/a since ~29 ka for the northern part of the LPF, and ~0.61 mm/a since about late Pleistocene, ~0.74 mm/a since ~65 ka, ~0.27 mm/a since ~45 ka for the southern part. The vertical slip for different part and different periods of the LPF shows different rates. In addition, the decrease of the vertical slip rates since late Pleistocene suggest that the activity of the LPF is becoming weak.

Keywords

• Langshan Piedmont Fault
• Hetao Basin
• Vertical slip rate
• Mountain-front terrace sequences