Deducing Crustal‐Scale Reverse‐Fault Geometry and Slip Distribution From Folded River Terraces, Qilian Shan, China. Issue 1 (7th January 2020)

• Record Type: Journal Article
• Authors: Wang, Yiran; Oskin, Michael E.; Zhang, Huiping; Li, Youli; Hu, Xiu; Lei, Jinghao
• Is Part Of: Tectonics. Volume 39:Issue 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-07
• Subjects: fluvial terrace -- Tibetan Plateau -- elastic model -- shortening -- kinematic model -- fault geometry; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2019TC005901
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The deep structure of active reverse faults is generally difficult to constrain from surface observations and may conceal shortening within the hinterland. Here we investigate the geometry of active, crustal‐scale reverse faulting from deformation of an unusually extensive set of river terraces preserved along the Beida River through the northwestern Qilian Shan. Two generations of fill terraces (T1 and T2) are well preserved from the foreland basin to at least 45 km within the hinterland. Optically stimulated luminescence and 10 Be dating methods indicate that T1 was abandoned at 24 ± 3 kyr B.P.; T2 was abandoned at 144 ± 30 kyr B.P. The T2 terrace profile reveals a long wavelength fold (~30 km) with a largest vertical deformation of ~120 m relative to T1. Both kinematic and elastic modeling of the deformed terraces indicate that folding is a result of movement along a steep reverse fault (~50 o ), which merges into a ~10° décollement at 15–17 km depth. Estimated slip at depth is 1.8 times higher than fault slip at the surface, indicating a substantial proportion of shortening is absorbed by folding of the range interior. The shortening rate since abandonment of T2 is 1.4 ± 0.4 mm/yr, which is consistent with previous research and makes up 23 ± 10% of the geodetic shortening rate across Qilian Shan orogen. Our results support that crustal‐scale reverse‐faulting accommodates shortening and northward propagation of the North Qilian mountain front and that the total shortening rate is distributed between multiple faults within the Qilian Shan and Hexi Corridor. Key Points: Stream terraces preserved at least 45 km within the range interior record long‐wavelength folding of the North Qilian Shan Both kinematic and elastic modeling of the deformed terraces reveal thick‐skinned nature of the underlying reverse fault Shortening rate of the North Qilian Shan is 1.4 ± 0.4 mm/yr, making up 23 ± 10% of geodetic shortening rate across Qilian Shan