image: BTC, Bikou thrust complex; TTC, Tangwangzhai thrust complex; LTC, Longwangmiao thrust complex
Credit: ©Science China Press
The controversial mechanism of klippes produced along the NE-striking Longmen Shan thrust belt (LSTB) in the eastern margin of the Tibetan Plateau, was the key point of comprehending tectonic evolution process of the LSTB. Traditional research proposed that the klippes are the front zone of the modern LSTB, while recent studies suggested that the klippes might be the result of Mesozoic thrusting of the LSTB. Nonetheless, there still remains a lack of crucial constraints regarding the emplacement time and formation mechanism of the klippes.
To address this, the research team collected rock samples from both the hanging wall and footwall of the Tangbazi and Woniuping klippes, which are two unique klippes differing from the others, and performed apatite and zircon separation and extraction. New results of (U-Th)/He dating and thermal history simulation of apatite and zircon are used to reveal klippe uplift and exhumation ages and to estimate the depth of denudation. Moreover, petrographic observations of the brecciated limestones surrounding the klippes were conducted based on structural and kinematic analysis. Combining with previous studies, a new tectonic model for the emplacement of the klippes in the LSTB was proposed.
Crucially, the study concludes that the Longmen Shan klippes experienced both thrusting and gliding process and may be eventually emplaced during the Late Eocene-Early Miocene. During the Late Triassic-Early Jurassic period, the northern segment of the LSTB formed the Bikou thrust complex in the north and the Tangwangzhai and Longwangmiao thrust complexes in the south due to the southward in-sequence propagation of the SW-Qinling orogenic foreland belt. Influenced by the far-field effects of the Lhasa-Qiangtang block collision and the late Yanshan movement, the northern segment of the LSTB and the northern Sichuan region experienced rapid uplift during the Late Cretaceous. During the Late Eocene-Early Miocene, the Tangwangzhai and Longwangmiao thrust complexes in the north segment of the LSTB glid towards the Sichuan basin along a detachment of the weak Silurian mudstones or phyllites, forming the klippes owing to gravity.
The research resolves the timing and emplacement of Longmen Shan klippes by integrating structural analysis, petrographic observations, and (U-Th)/He thermochronology. This work proposes a revised tectonic evolution model of the LSTB, highlighting the role of gravity in the propagation of thrust belt. The findings not only resolve regional tectonic controversies but also establish a model applicable to orogenic thrust belt worldwide.
Lin X, Yan D, Qiu L, Zhou Z, Song H, Kong F, Du C. 2025. Structural and (U-Th)/He thermochronological constraints on the Longmen Shan thrusting-gliding klippes, eastern margin of Tibetan Plateau. Science China Earth Sciences, 68(4): 1142–1157, https://doi.org/10.1007/s11430-024-1518-y