Underthrusting and duplexing beneath the northern Tibetan Plateau and the evolution of the Himalayan-Tibetan orogen

Abstract

The Cenozoic Qilian Shan thrust belt is the northern margin of the Tibetan Plateau, which developed in part due to progressive India-Asia convergence during Himalayan-Tibetan orogeny. Available geologic observations suggest that this thrust belt started deforming shortly after initial India-Asia collision at 60-55 Ma, and thus its kinematic development is intrinsically related to the construction and evolution of the Tibetan Plateau. Here, we present new field observations from a geologic traverse across the Qilian Shan to elucidate the style of deformation across the active thrust belt. In particular, we infer protracted out-of-sequence deformation here that is consistent with this thrust system remaining a stationary northern boundary to the Tibetan Plateau since the early Cenozoic. We present a lithosphere-scale model for this region that highlights the following: (1) coupled distributed crustal shortening and underthrusting of the North China craton beneath Tibet, which explains the spatial and temporal distribution of observed crustal shortening and thickness, (2) this underthrusting exploited the south-dipping early Paleozoic Qilian suture paleo-subduction mélange channel, and (3) development of a lower-crustal duplex at the lithospheric underthrusting ramp. This last inference can explain the relatively high elevation, low relief, and thickened crust of the central Qilian Shan, as well as the comparative aseismicity of the region, which experiences fewer earthquakes due to less upper-crustal faulting. Both the northern and southern margins of the Himalayan-Tibetan orogen appear to have developed similarly, with continental underthrusting and crustal-scale imbrication and duplexing, despite vastly different climatic and plate-velocity boundary conditions, which suggests that the orogen-scale architecture of the thrust belt is controlled by neither of these forcing mechanisms. Instead, strength anisotropies of the crust probably control the kinematics and style of deformation, including the development of northern Tibet, where thrust systems are concentrated along pre-Cenozoic suture zones.

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 interplay between climate and tectonics during the upward and outward growth of the Qilian Shan orogenic wedge, northern Tibetan Plateau

“…The Qilian Shan consists of a series of subparallel NW-SE striking ranges that grow on folds, thrusts or strike-slip faults accommodating the northward motion of the Tibetan plateau (Allen et al, 2017;Cheng et al, 2019b;George et al, 2001;Meyer et al, 1998;Yin et al, 2002;Yuan et al, 2013;Zhang et al, 2017;Zheng et al, 2017;Zheng et al, 2013a;Zhuang et al, 2011a;Zhuang et al, 2011b;Zuza et al, 2016;Zuza et al, 2018a;Zuza et al, 2017) ( Fig. 1).…”

“…However, the average elevation of the Qilian Shan decreases northward gradually, from over 4.5 km in the hinterland of the SQS to less than 3 km at the northern front of the NQS and to less than 2 km along the northern margin of the Jiuquan basin to the north.The wide width of the active Qilian Shan and distribution of active faulting (or recently active faulting) throughout the Qilian Shan probably require a weak basal detachment (with low friction). The exploitation of the early Paleozoic suture zones by Cenozoic thrust faults suggests that these south-dipping suture zones are important for the Cenozoic Qilian Shan(Zuza et al, 2018a; Zuza et al, 2018b), probably acting as weak detachment horizons that enabled deformation to quickly propagate ~2000 km north of the India-Asia collisional front.…”

Geologic framework of the northern Indo-Burma Ranges and lateral correlation of Himalayan-Tibetan lithologic units across the eastern Himalayan syntaxis

“…Tapponnier et al, 1981;Ni et al, 1989;Mitchell, 1993;Haq and Davis, 1997;Haproff et al, 2018). Establishing the geologic history of the two flanking belts is crucial for understanding the holistic development of the Himalayan collisional system and differentiating the end-member models of continental deformation during the India-Asia collision (e.g., Tapponnier et al, 1982Tapponnier et al, , 2001England and Houseman, 1986;Cobbold and Davy, 1988;Dewey et al, 1988;England and Molnar, 1990;Royden et al, 1997;Zuza et al, 2019).…”