Partitioning of oblique convergence coupled to the fault locking behavior of fold‐and‐thrust belts: Evidence from the Qilian Shan, northeastern Tibetan Plateau

Abstract

Oblique plate convergence is common, but it is not clear how the obliquity is achieved by continental fold‐and‐thrust belts. We address this problem in the Qilian Shan, northeastern Tibetan Plateau, using fieldwork observations, geomorphic analysis, and elastic dislocation modeling of published geodetic data. A thrust dips SSW from the northern range front and underlies steeper thrusts in the interior. Cenozoic thrust‐related shortening across the Qilian Shan is ~155–175 km, based on two transects. Elastic dislocation modeling indicates that horizontal strain in the interseismic period is consistent with oblique slip on a single low‐angle detachment thrust below ~26 km depth, dipping SSW at ~17°. We suggest that this detachment is located above North China Block crust, originally underthrust during Paleozoic orogeny. Horizontal shear strain is localized directly above the updip limit of creep on the detachment and is coincident with the left‐lateral Haiyuan Fault. This configuration implies that oblique slip on the detachment below seismogenic depths is partitioned in the shallow crust onto separate strike‐slip and thrust faults. This is consistent with strain partitioning in oceanic subduction zones but has not previously been found by dislocation models of continental interiors. The marginal, strike‐slip, Altyn Tagh Fault influences thrusting within the Qilian Shan for 100–200 km from the fault but does not control the regional structure, where Paleozoic basement faults have been reactivated. The Qilian Shan resembles the main Tibetan Plateau in nascent form: active thrusts are marginal to an interior that is developing plateau characteristics, involving low relief, and low seismicity.

Tectonics of the Eastern Kunlun Range: Cenozoic Reactivation of a Paleozoic‐Early Mesozoic Orogen

“…Compressive stresses resulting from protracted India‐Eurasia convergence transferred rapidly northward to the Eastern Kunlun Range by ca. 50 Ma and also affected the Qilian Shan to the north in the Eocene (e.g., Allen et al, ; Gaudemer et al, ; Zuza et al, , ). The Triassic Neo‐Kunlun suture may have reactivated along a zone of strain localization superposed on the inferred flexural bulge during the Miocene, which is resulted from the onset of Cenozoic uplift of the Eastern Kunlun Range.…”

“…The original configuration of the exposed bedrock has been modified by early Mesozoic extension, resulting from the closure of the Meso‐ and Paleo‐Tethys Oceans (Cheng et al, ; Pullen et al, ; Wu et al, ; Wu et al, ; Zhang et al, ; Zuza et al, ), and Cenozoic intracontinental deformation associated with the India‐Asia collision (Vincent & Allen, ; Yin & Harrison, ; Chen et al, ; X. Cheng, Fu, et al, F. Cheng, Guo, et al, ; Zuza et al, , ; Allen et al, ). Below we briefly outline the important Phanerozoic tectonic events that affected Kunlun‐Qaidam terrane.…”

Deducing Crustal‐Scale Reverse‐Fault Geometry and Slip Distribution From Folded River Terraces, Qilian Shan, China

“…In these cross‐section models, shallow faults dip between 25° and 50°. Conversely, Allen et al () estimates a steep dip angle for the North Qilian fault, ~45° , based on focal mechanism and fault outcrops in the field. Their elastic dislocation model of GPS data indicates that this fault roots into a décollement below 26 km depth, dipping SSW at ~17°.…”

Cenozoic Exhumation of the Qilian Shan in the Northeastern Tibetan Plateau: Evidence From Low‐Temperature Thermochronology

“…Magnetostratigraphy from the Ganyanchi pull‐apart basin dates the formation of the basin to ~3 Ma (Lei et al, 2018), suggesting that the left‐lateral strike‐slip movement along the Haiyuan fault began at approximately 3 Ma. (c) Bedrock matching estimates the left‐slip offset on the Haiyuan fault as ~10 km in the west and 10.5–15.5 km in the east (Allen et al, 2017; Burchfiel et al, 1991; Zhang et al, 1991). The slip rates along the Haiyuan fault have been estimated by geological methods at 4–6 mm/yr since the late Quaternary (Li et al, 2009; Zhang et al, 2017) and by GPS at 4–5 mm/yr during the past several decades (Duvall & Clark, 2010; Zheng, Zhang, He, et al, 2013).…”