The Longmen Shan thrust belt (LSTB), marking the eastern margin of the Tibetan Plateau, has long been a focal point of geotectonic research due to its complex structural features and dynamic evolution. Among the most enigmatic elements of this region are the klippes—isolated thrust slices of rock that have been variously interpreted in tectonic models. Traditional perspectives posited these klippes as the frontal zone of an actively deforming thrust belt, whereas more recent hypotheses suggested they originated from Mesozoic thrusting episodes. Yet, the emplacement timing and mechanisms controlling the formation of Longmen Shan klippes have remained insufficiently constrained, hindering a comprehensive understanding of the region’s tectonic history.
To resolve these ambiguities, a multidisciplinary study led by Lin et al. employed a combination of detailed field observations, petrographic analyses, and advanced thermochronological techniques, specifically (U-Th)/He dating on apatite and zircon mineral phases. Rock samples were meticulously collected from both the hanging wall and footwall strata of two particularly distinctive klippes—Tangbazi and Woniuping—selected for their unique structural characteristics relative to other regional klippes. This integrative approach was designed to elucidate the uplift and exhumation history of these thrust slices, alongside quantifying the depth and timing of denudation processes.
The authors utilized (U-Th)/He thermochronology, a high-resolution geochronological method capable of recording low-temperature cooling histories, to reconstruct thermal evolution and tectonic exhumation sequences. Apatite and zircon crystals extracted from the sampled rocks provided complementary cooling ages, allowing for the discrimination between distinct phases of tectonic activity and sedimentary burial. Coupled with thermal history modeling, these data revealed significant insights into the timing of klippe emplacement and the rates of uplift. The results underscore that the klippes underwent complex thrusting and subsequent gravitational gliding processes, culminating in their emplacement primarily during the Late Eocene to Early Miocene interval.
A pivotal finding of this study is the timing and structural control of thrust complexes along the northern segment of the LSTB. During the Late Triassic to Early Jurassic periods, intense tectonic activity led to the formation of three prominent thrust complexes—Bikou in the north, and Tangwangzhai and Longwangmiao further south. These thrust complexes evolved as a consequence of southward in-sequence propagation linked to the SW-Qinling orogenic foreland belt, a major tectonic regime that influenced much of eastern Asia’s lithospheric deformation during this era.
Subsequent tectonothermal events profoundly affected the northern LSTB and the wider northern Sichuan region. The collision between the Lhasa and Qiangtang terranes, paired with the late-Yanshanian orogeny, induced rapid crustal uplift during the Late Cretaceous. These far-field tectonic stresses set the stage for later structural modifications, including the detachment and gravitational sliding processes responsible for klippe formation. This interplay of tectonic inheritance and new deformational pulses reflects the complex multi-phase evolution of the Tibetan Plateau margin.
Intriguingly, the Tangwangzhai and Longwangmiao thrust complexes were found to have undergone gravity-driven gliding toward the Sichuan basin, facilitated by the presence of mechanically weak Silurian mudstone and phyllite layers acting as basal detachment surfaces. This gliding mechanism challenges the simplistic thrust-only models previously held and emphasizes the importance of gravitational spreading and basal detachment in shaping the structural architecture of active orogenic belts. Such insights lend themselves to a broader understanding of the kinematics of thrust belt propagation under varying lithological and tectonic conditions.
Petrographic observations of brecciated limestones surrounding the klippes provided further supporting evidence on deformation styles, revealing fracture networks and mineralogical textures consistent with high-strain thrust and glide regimes. Structural and kinematic analyses of fault rocks and mylonites added constraints to the timing and direction of motion, which corroborated the thermochronological data and proposed emplacement mechanisms. This multi-pronged approach allowed for a more holistic interpretation of complex fault-bend folding, segmentation, and associated mass transport in the upper crust.
The study’s comprehensive integration of structural geology, petrography, and thermochronological data culminated in a robust new tectonic evolutionary model for the Longmen Shan thrust belt. This model recognizes the key roles that both tectonic shortening and gravitational forces play in the lateral propagation and emplacement of klippes. By reconceptualizing the relationship between thrusting and basal glide as a coupled process, it offers a paradigm shift in how geoscientists interpret orogenic wedge dynamics globally.
Furthermore, these findings carry implications beyond the Longmen Shan region. The mechanisms elucidated by this research provide a critical analog for thrust belts worldwide, particularly those characterized by sequences of mechanically weak detachment horizons juxtaposed with rigid thrust blocks. By resolving longstanding regional tectonic controversies related to timing and kinematic evolution, the study fosters improved predictive frameworks for seismic hazard assessment, natural resource exploration, and mountain building processes in convergent plate boundary zones.
Importantly, the successful application of (U-Th)/He thermochronology in constraining episodes of thrusting and gliding underscores the growing utility of low-temperature thermochronometers in orogenic research. The sharp temporal resolution achieved enables the discrimination of overlapping tectonic events that are otherwise indistinguishable through conventional structural mapping or higher-temperature geochronology. This methodological advancement represents a significant step forward in unraveling the complex histories inherent to major thrust belts on Earth.
In sum, the research by Lin and colleagues delivers a landmark contribution to the geological sciences by offering a more nuanced, time-resolved, and process-oriented understanding of thrust belt dynamics at the eastern margin of the Tibetan Plateau. The refined tectonic model not only clarifies the elusive origins and emplacement histories of Longmen Shan klippes but also enriches the global narrative of mountain belt formation through combined tectonic and gravitational forcings.
The implications of understanding such processes are vast, ranging from refining models of continental deformation under varying stress regimes to informing landscape evolution and sedimentary basin development in active orogenic zones. As tectonic studies continue to embrace integrative methodologies, this research exemplifies the power of combining petrography, structural geology, and cutting-edge thermochronology to decode Earth’s dynamic crustal processes.
Subject of Research: Structural and thermochronological analysis of klippe emplacement and tectonic evolution of the Longmen Shan thrust belt, eastern margin of the Tibetan Plateau.
Article Title: Structural and (U-Th)/He thermochronological constraints on the Longmen Shan thrusting-gliding klippes, eastern margin of Tibetan Plateau.
News Publication Date: 2025.
Web References: http://dx.doi.org/10.1007/s11430-024-1518-y
References: Lin X, Yan D, Qiu L, Zhou Z, Song H, Kong F, Du C. 2025. Science China Earth Sciences, 68(4): 1142–1157.
Image Credits: ©Science China Press
Keywords: Longmen Shan thrust belt, klippes, tectonic evolution, (U-Th)/He thermochronology, apatite dating, zircon dating, thrusting and gliding, tectonic uplift, exhumation, detachment fault, gravitational gliding, Tibetan Plateau, orogenic processes
