Abstract
The Qilian Shan, which is located along the northeastern margin of the Tibetan Plateau, plays a key role in understanding the dynamics of the outward and upward growth of the plateau. However, when and how tectonic deformation evolved into the geographic pattern which is currently observed in the Qilian Shan are still ambiguous. Here, apatite fission track (AFT) thermochronology and sedimentology were conducted to interpret the low-temperature tectonic deformation/exhumation events in well-dated Late Miocene synorogenic sediment sequences in the Xining Basin, which is adjacent to the southern flank of the Qilian Shan. These new low-temperature thermochronological results suggest that the Qilian Shan experienced four stages of tectonic exhumation during the late Mesozoic–Cenozoic. The Late Cretaceous exhumation events in the Qilian Shan were caused by the diachronous Mesozoic convergence of the Asian Plate and Lhasa Block. In the early Cenozoic (ca. 68–48 Ma), the Qilian Shan quasi-synchronously responded to the Indian–Asian plate collision. Subsequently, the mountain range experienced a two-phase deformation during the Eocene–Early Miocene due to the distal effects of ongoing India–Asia plate convergence. At ca. 8 ± 1 Ma, the Qilian Shan underwent dramatic geomorphological deformation, which marked a change in subsidence along the northeastern margin of the Tibetan Plateau at that time. Our findings suggest that the paleogeographic pattern in the northeastern Tibetan Plateau was affected by the pervasive suture zones in the entire Qilian Shan, in which the pre-Cenozoic and Indian–Asian plate motions reactivated the transpressional faults which strongly modulated the multiperiodic tectonic deformation in northern Tibet during the Cenozoic. These observations provide new evidence for understanding the dynamic mechanisms of the uplift and expansion of the Tibetan Plateau.
Highlights
With continuous Cenozoic compression and convergence between the Indian and Asian plates, the uplift and expansion of the Tibetan Plateau has profoundly influenced the climatic and paleogeographical evolution in Asia (England and Houseman, 1986; Harrison et al, 1992; Dupont-Nivet et al, 2008; Fang et al, 2019; Spicer et al, 2020)
All the measured paleocurrent results are characterized by a dominant southerly current direction, and the sedimentary facies and stratigraphic lithology are similar, allowing correlation between the two sections. These findings suggest that the sediments from the Precambrian basement strata in the south are bounded by the Daban Shan in the eastern part of the Qilian Shan and were the main source area supplying the basin during the Late Miocene–Early Pliocene (Yang et al, 2017; Zhang et al, 2017)
The amount of crustal thickening and pervasive suture zones in the northeastern Tibetan Plateau prior to the collision remain unclear, the new detrital apatite fission track (AFT) analysis results in this study indicate that the widespread pre-collisional deformation region may have influenced the tectonics of the current northern margin of the Tibetan Plateau
Summary
With continuous Cenozoic compression and convergence between the Indian and Asian plates, the uplift and expansion of the Tibetan Plateau has profoundly influenced the climatic and paleogeographical evolution in Asia (England and Houseman, 1986; Harrison et al, 1992; Dupont-Nivet et al, 2008; Fang et al, 2019; Spicer et al, 2020). Recent deforming mantle models suggest that the deformation initiated quasi-synchronously in the early Cenozoic throughout the whole Tibetan Plateau (for example, Yin and Harrison, 2000; Yin et al, 2008; Dayem et al, 2009; Clark, 2012; Clark et al, 2010). Two consensuses have emerged regarding the timing of prominent deformation in the Qilian Shan, namely, the early Cenozoic (Yin et al, 2002; Yin et al, 2008; He et al, 2017; He et al, 2020a; He et al, 2020b) and the late Cenozoic (Wang et al, 2017; Pang et al, 2019a; Wang et al, 2020), and these models yield distinctly different predictions of the mechanism of the plateau growth. Cretaceous tectonic signals have been found in the Qilian Shan (Jolivet et al, 2001; Qi et al, 2016; Li et al, 2019), but research regarding the Mesozoic tectonic evolution of the southern, central, and northern Qilian Shan is relatively scarce (Vincent and Allen 1999; Chen et al, 2002; Cheng et al, 2019)
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