Stepwise decrease in strike-slip rate along the eastern Altyn Tagh Fault and its relation to the Qilian Shan thrust system, northeastern Tibetan Plateau

Abstract

As the northern boundary fault the Tibetan Plateau, the slip-rate decrease pattern of the eastern Altyn Tagh Fault (ATF) and its relation to the neighboring Qilian Shan thrust system remain unclear. In this study, high-resolution topographic data have been acquired by using the UAV-based LiDAR and Structure from Motion (SfM) technique. Using OSL dating ages obtained from terraces, we constrained the strike-slip rates at four locations along the eastern ATF, ranging from ∼7 mm/yr to ∼1 mm/yr. In combination with previous observations, a stepwise decrease pattern in strike-slip rate along the eastern ATF has been proposed in this study. To confirm this conclusion, sandbox experiments were conducted to simulate the simultaneous deformation involving the sinistral slip of the eastern ATF and the crustal shortening in the northeastern Tibetan Plateau. The role of ductile middle-lower crust was examined by comparative experiments (Models 1 and 2). In Model 1, without a ductile middle-lower crust, the wedge translated forward as a rigid block until reaching the frontal thrust, resulting in an almost uniform slip rate along the strike-slip fault. In Model 2, with a ductile middle-lower crust, the slip rate exhibited rapid decrease while passing each thrust belt, forming a stepwise decrease pattern rather than a gradient decrease; The compressional deformation was accommodated by a series of thrust belts that were active simultaneously, consistent with the late Quaternary simultaneous activity of the thrust belts within the Qilian Shan thrust system. Our modeling results suggested coupled growth between the eastern ATF and the Qilian Shan thrust system, and that a ductile middle-lower crust played important role in dispersing deformation into parallelly distributed thrust belts.