Latest Pleistocene to Holocene Thrusting Recorded by a Flight of Strath Terraces in the Eastern Qilian Shan, NE Tibetan Plateau

Abstract

At the eastern Qilian Shan mountain front in the NE Tibetan Plateau, the Minle‐Damaying Fault (MDF), the southernmost fault of the North Frontal Thrust (NFT) system, has previously been proposed as an inactive structure during the Holocene. Here we present a detailed record of six strath terraces of the Xie River that document the history of active deformation of the MDF. One optically stimulated luminescence dating sample constrains abandonment of the highest terrace T6 at 12.7 ± 1.4 ka. The formation ages of the lower terraces (T4–T1) are dated by AMS 14C dating. The cumulative vertical offsets of the MDF recorded by these terraces are determined as 12.2 ± 0.4 m (T6), 8.0 ± 0.4 m (T5), 6.4 ± 0.4 m (T4), 4.6 ± 0.1 m (T3), and 3.2 ± 0.2 m (T1c) by an unmanned aerial vehicle system, respectively. A long‐term vertical slip rate of the MDF of 0.9 ± 0.2 mm/yr is then estimated from the above data of terrace age and vertical offset by a linear regression. Assuming that the fault dip of 35 ± 5° measured at the surface is representative for the depth‐averaged fault dip, horizontal shortening rates of 0.83–1.91 mm/yr are inferred for the MDF. Our new data show that the proximal fault (the MDF) of the NFT system at the eastern Qilian Shan mountain front has remained active when the deformation propagated basinward, a different scenario from that observed at both the western and central Qilian Shan mountain front.

Segmented Thrust Faulting: Example From the Northeastern Margin of the Tibetan Plateau

“…The Xie River site (N37°51′11.44″, E101°35′10.36″) is located along a tributary of the Dongda River (Figure c), with a confluence located immediately north of the MDF. Xiong et al () describe six generations of stream terraces, T1c through T6, most of which are very well preserved (Figure c) and mapped continuously across the MDF. Here we use the same terrace designation as Xiong et al ().…”

“…Xiong et al () describe six generations of stream terraces, T1c through T6, most of which are very well preserved (Figure c) and mapped continuously across the MDF. Here we use the same terrace designation as Xiong et al (). The stratigraphy of each terrace comprises the upper silty overbank sediments and the conglomerates representing the fluvial bedload.…”

“…The height of the scarps increases from T1c through T6 (Figure a), indicating multiple paleoseismic events. To assess the heights and errors of these scarps, we remeasured the scarp heights from a DEM generated from previously published drone imagery (Xiong et al, ) (Figure a). The model has a vertical precision of 0.2 m and covers an area of 0.5 km 2 across the MDF.…”

“…To ensure the accuracy of the DEM, 11 control points were set uniformly across the scanned area and precisely located with real‐time kinematic GPS to 0.2‐m vertical precision. The resulting DEM was previously published by Xiong et al (), and here we analyzed this data to determine scarp heights. A three‐line‐profile normal to the strike is used to extract the scarp height.…”

Paleoearthquakes and Rupture Behavior of the Lenglongling Fault: Implications for Seismic Hazards of the Northeastern Margin of the Tibetan Plateau

“…However, the earthquake behavior and seismic hazards of this area remain poorly understood. The late Quaternary tectonic deformation in the NE Tibetan Plateau is partitioned into localized left‐lateral shearing along the Qilian‐Haiyuan fault zone and distributed crustal shortening and thickening across the Qilian Shan fold‐and‐thrust zone (Allen et al, ; Hu et al, ; Xiong et al, ; Zheng et al, ), indicating that the Qilian‐Haiyuan fault zone is subject to long‐term stress accumulation and thus represents high seismic risk. The 1920 M 8.5 Haiyuan earthquake that ruptured the Haiyuan fault, along the eastern section of the fault zone, is the largest historical earthquake in the northeastern margin of the Tibetan Plateau (Deng et al, ; W. Q. Zhang et al, ).…”