Seismic reflection evidence of crustal duplexing and lithospheric underthrusting beneath the western Qilian Mountains, northeastern margin of the Tibetan Plateau

Abstract

The geological processes responsible for outward growth of the Tibetan Plateau are debated. The Qilian Mountains on the northeastern margin of the plateau comprise one of the youngest structural components of the plateau whose understanding is key to deciphering the broader geological evolution of the region. Here, based on a reprocessed deep seismic profile which was originally collected during the 1990s across the northeast margin of the western Qilian Mountains and previous geological and geophysical data, we find evidence for decoupled crustal deformation that was partitioned by a decollement, in which lowercrustal deformation featured by local duplexing preceded upper-crustal deformation featured by imbricate thrusts. Furthermore, we propose that the Asian lithospheric mantle is being underthrust beneath the western Qilian Mountains, as inferred from patterns of lower crustal deformation which is marked by the Moho geometry. Integrating these results yields a better understanding of lithospheric deformation of western Qilian Mountains, northeastern margin of the plateau during the Cenozoic.

Crustal structure and deformation mechanism of the western northeast Tibetan Plateau

“…In the western segment, the Moho depth is notably deeper than that in the middle-eastern Qilian Shan fold-thrust belt, with a maximum depth of 73 km beneath Hala Lake, as substantiated by studies (Cui et al, 1995;Gao et al, 1999;Jolivet et al, 2001;Huang et al, 2021). This observation supports the hypothesis that the most concentrated convergent stress is accommodated through crustal deformation in the western segment.…”

“…Sedimentation in the Jiuquan Basin initiated in the Mesozoic, and this northwest-trending basin was subsequently influenced by the uplift of NQLS. Deep seismic reflection profiles reveal that the thickness of the Cenozoic sedimentary cover ranges between 1.5 and 2 km (Song et al, 2001;Huang et al, 2018).…”

“…Since the 1970s (Burke and Dewey, 1973;Molnar and Tapponnier, 1975), numerous end-member models have been proposed to explain the formation of the Tibetan Plateau, as a result of intensive study (Figure 1). In the northeastern Tibetan Plateau, these models include (1) Cenozoic underthrusting of the Asian lithosphere beneath the Tibetan Plateau (Willett and Beaumont, 1994;Kind et al, 2002;Zhao et al, 2011;Feng et al, 2014;Ye et al, 2015); (2) coupled distributed crustal shortening and underthrusting of the Alxa Block beneath Tibet, accounting for the observed crustal shortening and thickness distribution (England and Houseman, 1986;Dewey et al, 1997;Huang et al, 2018;Xiong et al, 2019;Zuza et al, 2019); (3) vertical inflation of the Tibetan crust due to lateral mid-lower crustal channel flow (Zhao and Morgan, 1987;Bird, 1991;Royden et al, 1997;Clark and Royden, 2000); and (4) intracontinental subduction facilitated by large-scale strike-slip faults (Zuza et al, 2016;Wu et al, 2023b).…”

Growth of Northern Tibet: Insights From the Crustal Shear Wave Velocity Structure of the Qilian Shan Orogenic Belt

“…The ambiguity is caused by the fact that most of these images focus on the large‐scale structure. Despite the existence of seismic reflection and refraction profiles (X. Huang et al., 2021; Jia et al., 2019; M. Liu et al., 2006; Z. Zhang et al., 2013), three‐dimensional (3‐D) images of the crustal velocity structure with sufficient resolution are still needed.…”

“…Despite the existence of seismic reflection and refraction profiles (X. Huang et al, 2021;Jia et al, 2019;M. Liu et al, 2006;, three-dimensional (3-D) images of the crustal velocity structure with sufficient resolution are still needed.…”