Kinematics of Late Quaternary Slip along the Yabrai Range-front Fault: Implications for Cenozoic Tectonics across the Gobi Alashan Block, China

Abstract:

The Yabrai range-front fault (YRF) accommodates deformation within the middle Gobi Alashan block between Tibetan Plateau and the Ordos block. As such, it affords an opportunity to examine the transition between shortening and crustal thickening associated with growth of the Tibetan Plateau and extension in North China. Geomorphic mapping of the active fault trace and trench investigations reveal that the YRF is comprised of three segments with variable fault strike, sense of motion, scarp height, and slip history. Displaced Holocene and Late Pleistocene alluvial deposits indicate that southwestern segment is characterized by oblique-normal displacement with a minor left-lateral component, whereas the middle segment appears to exhibit dip-slip normal displacement. The northeastern segment appears to be primarily a left-lateral strike-slip fault. Geomorphically fresh fault scarps are present within Late Pleistocene-Holocene alluvial fans and terraces along the southwestern and northeastern segments, whereas the middle segment of the fault is coincident with the bedrock alluvial contact along the range front. Along the southwestern segment, ¹⁰Be exposure ages of offset fans yield a vertical slip rate of ~0.1 mm/yr over the late Pleistocene. Strike-slip rates along the northeastern fault segment are between 0.23 ± 0.02 and 0.78 ± 0.12 mm/yr. Regionally, the orientation, sense of motion, and slip rates along the Yabrai range-front fault is consistent with both NE-directed shortening across the margin of the Tibetan Plateau and NW-derected extension across the Ordos Block.