Late Cretaceous – Cenozoic thermal structure and exhumation of the Eastern Tibetan Plateau margin: A doubly-vergent orogenic wedge
Graphical abstract
Cross-section sketch showing the disrupted and fossilized thermal structure of the Eastern Tibetan Plateau margin.
Introduction
The Eastern Tibetan Plateau margin, with mean surface elevations of 4–4.5 km above sea level, is boarded on its eastern side by a 400 km-wide system of mountain ranges with peaks reaching up to 6 km above sea level (Fig. 1, Fig. 2). Topographically and structurally it has some similarities with the southern margin of the Tibetan Plateau and its peripheral Himalayan Mountain Range system (Fig. 2; transects P1-P2 and P3-P4). Mean surface elevation falls to the east across the eastern mountain range system, most dramatically over the last 30 km of it, to a few hundred metres above sea level in the Sichuan Basin. The Longmen Shan is the name for the outer mountain ranges closest to the Sichuan Basin.
The structure of the upper crust beneath the mountain belt system involves several major northwest-dipping listric thrust faults considered to sole-out into a horizontal mid-crustal detachment (Hubbard and Shaw, 2009). This structural interpretation is consistent with other analyses of the 2008 Wenchuan Earthquake (de Michele et al., 2010; Qi et al., 2011; Fielding et al., 2013), although variations of it have been reported by Robert et al. (2010), Li et al. (2013) and Feng et al. (2016). The overall tectonic structure appears to conform to an intra-continental orogenic wedge. We use the informal term “Eastern Tibetan Plateau margin” to refer to this wedge as well as the easternmost part of the high Tibetan Plateau, and the western part of the Sichuan Basin that contains thrust faults associated with the wedge, as far as the Longquan Shan (range) within the basin. The Longmen Shan Thrust Belt (LSTB) has historically been used for the part of the imbricate wedge between the Sichuan Basin and the Wenchuan-Maoxian Fault (WMF), located some 40–50 km into the mountain belt from the Sichuan Basin. Here, we extend the LSTB as a name for the mountain range system as far west as the Longriba Fault System, which is the first major fault system east of the high plateau, such that the LSTB encompasses the whole of the wedge deformation zone. Our study is limited to the part of the eastern Tibetan Plateau margin, north of the Xianshuihe Fault, which is the northernmost of the major transcurrent faults that facilitate tectonic extrusion of the upper crust underlying the plateau towards the South China Block (Fig. 1).
Numerous low-temperature thermochronological studies have been undertaken within the LSTB during the past 25 years, attracted by the opportunity to constrain the timing and extent of exhumation of the LSTB. These studies have established two key features: (i) the greatest amount of exhumation has been associated with the highest elevation mountain ranges, and (ii), the Late Cenozoic timing of substantial exhumation (e.g. Arne et al., 1997; Xu and Kamp, 2000; Wang et al., 2012) conforms with the timing of substantive exhumation along the southern margin of the Tibetan Plateau and Himalaya Mountain Range (e.g. Copeland et al., 1995; Lee et al., 2011; Nadin and Martin, 2012; Carrapa et al., 2014). Numerous low-temperature thermochronological studies of the Eastern Tibetan Plateau margin, and in particular the Longmen Shan Thrust Belt (LSTB), as previously defined, have subsequently been published (e.g. Tian et al., 2013; Tan et al., 2014, Tan et al., 2019; Ansberque et al., 2018; see a review in Supplementary material online, which includes a comprehensive reference list), which have fleshed-out important details about the amounts, timing, and rates of Late Cenozoic exhumation within and between the major thrust faults of the LSTB.
Modern rates of geodetic strain markedly decrease across the Longriba Fault System (Guo et al., 2015) where the high plateau transitions from passive uplift, with minimal exhumation, into the imbricate wedge structure of the LSTB, characterized by pervasive uplift and exhumation. The Sichuan Basin developed as a 3–5 km deep foreland basin during the Late Triassic and Early Jurassic as a result of loading due to shortening of prior passive margin northwest-dipping normal faults and overthrusting of the Songpan-Ganzi Terrane across the zone of inverted structures (Chen et al., 1994; Burchfiel et al., 1995). Late Cenozoic shortening has accentuated the imbrication and steepened the faults close to the surface, resulting in limited further flexure of the basin and sediment accumulation. Various models have been proposed to accommodate the shortening within the lithosphere beneath the mid-crustal detachment fault. We do not comment upon this debate here, because low-temperature thermochronology data cannot uniquely discriminate between exhumation due to imbricate thrusting in the upper crust versus any passive exhumation of the upper crust inferred to have been driven from below it.
New petrological data on greenschist and higher-grade metamorphic rocks within the eastern part of the LSTB, coupled with new 40Ar/39Ar geochronological data, has started a debate about the proportion of Cretaceous versus Late Cenozoic exhumation across the LSTB (Tian et al., 2016; Xue et al., 2017, Xue et al., 2021; Airaghi et al., 2017a, Airaghi et al., 2017b, Airaghi et al., 2018a, Airaghi et al., 2018c; Zhang et al., 2020). However, most published low-temperature thermochronology studies within the eastern part of the LSTB have yielded Late Cenozoic ages, reflecting the lower closure temperatures of those systems. Here, we take two approaches to contribute to this debate: (i) we present data for samples from sites in western and eastern areas peripheral to the LSTB, both up on the plateau and in the western Sichuan Basin, and (ii), we present new data for four vertical sections in those peripheral areas together with linking surface samples. We integrate these data with published data for two additional vertical sections, one up the Pengguan Massif and the other up the Xuelongbao Massif (Wang et al., 2012; Furlong et al., 2021). This extended data set enables us to partition, in space and time, the Cretaceous versus Late Cenozoic components of exhumation across the whole of the Eastern Tibetan Plateau margin. In doing so, we appeal to interpretation of biotite Ar ages from samples of the Xuelongbao Massif to constrain the total amount of Late Cretaceous exhumation there. Of the vertical sections with new data, three are deep drill holes (6.6–7.2 km deep; HC-1, LS-1 & CK-1) and one is an outcrop vertical section (Yanggonghai granitoid). All of the apatite and zircon fission track and most of the zircon (U-Th)/He data for the six vertical sections (including the Pengguan and Xuelongbao massifs) and the linking surface samples were generated by the same analysts in the University of Waikato (New Zealand) laboratory.
Section snippets
Geological setting of the Eastern Tibetan Plateau margin
The Eastern Tibetan Plateau margin is composed of three distinctive morphotectonic units from west to east. (i) The Songpan-Ganzi Terrane forms a significant part of the Tibetan Plateau interior. (ii) The Longmen Shan Thrust Belt marks the plateau margin and fringing mountain belt. (iii) The Sichuan Basin is a low-elevation foreland basin (Fig. 3).
The triangular-shaped Songpan-Ganzi Terrane or Fold Belt is located on the northeastern Tibetan Plateau and is bounded to the east by the
Low-temperature age structure of the Eastern Tibetan Plateau margin
What we learn from the geological setting of the Eastern Tibetan Plateau margin, including the Longmen Shan Thrust Belt, is that there are few stratigraphic relationships that help constrain the timing and magnitude of Cretaceous – Cenozoic vertical crustal displacements in this orogen. This makes the orogen fertile for the application of low-temperature thermochronology methods that enable the magnitude and timing of exhumation to be established, appealing to a fossilized thermal signal locked
Samples and analytic methods
We collected 33 samples along a NE-SW-trending transect from the Zoige Block across the LSTB and into the western Sichuan Basin. This included outcrop samples and unwashed cutting samples from three deep (6+ km) drill-holes (HC-1, LS-1 and CK-1) (Fig. 3; Table 1). Each Drill-hole sample was taken across stratigraphic ranges of no >50 m. Zircon and apatite grains were separated using standard crushing, heavy liquid and magnetic separation techniques. We applied fission track analysis to all of
Results and interpretations
All AFT, ZFT and ZHe results are presented in Table 1, Table 2, Table 3. Radial plots and histogram statistics for single-grain AFT and ZFT data are presented in Supplementary Figs. S1 – S5. All age errors are quoted at the 1σ level. The new AFT and ZFT pooled or central ages (and associated single-grain ages) for surface and vertical section samples along the NE-SW transect (Fig. 3), together with the stratigraphic ages of sample host rocks, are plotted against distance across the field area
Discussion
The foregoing sections of this paper have established that the 400 km-wide Eastern Tibetan Plateau margin has experienced three exhumation episodes (Early Cretaceous, Late Cretaceous and Late Cenozoic). This has been revealed by a review of published data, and particularly from the new data reported and interpreted here. These low-temperature thermochronology results have mainly identified the magnitude and geographic extent of the latter two episodes. While we have noted particular sample data
Conclusions
Interpretation of low-temperature thermochronology data for two vertical sections in outcrop (published) and new data reported here for four vertical sections (outcrop and drill hole), and linking surface samples, along a NW-SE transect across the 400 km-wide Eastern Tibetan Plateau margin and the Longmen Shan Thrust Belt, has enabled us to draw the following conclusions:
- 1.
Multiple low-temperature thermochronological systems (AFT, ZFT and ZHe) applied to samples from steep vertical sections in
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was supported by the National Natural Science Foundation of China (Grant Nos. 42230310, 41230313, 41472107, 41572111) and the “Mount Everest Research Plan” of the Chengdu University of Technology (Grant No. 80000-2021ZF11408). Internal research funding in support of this research project was also provided by the University of Waikato, Hamilton (New Zealand). We acknowledge three reviewers for their constructive comments on the manuscript.
References (135)
- et al.
Microstructural vs. compositional preservation and pseudomorphic replacement of muscovite in deformed metapelites from the Longmen Shan (Sichuan, China)
Lithos
(2017) - et al.
Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): constraints from petrology and thermobarometry
J. Asian Earth Sci.
(2017) - et al.
Differential exhumation in response to episodic thrusting along the eastern margin of the Tibetan Plateau
Tectonophysics
(1997) - et al.
Quantifying rates of landscape evolution and tectonic processes by thermochronology and numerical modeling of crustal heat transport using PECUBE
Tectonophysics
(2012) - et al.
Emplacement of the Longmen Shan thrust-nappe belt along the eastern margin of the Tibetan Plateau
J. Struct. Geol.
(1996) - et al.
The evolution of the western Sichuan foreland basin, southwestern China
J. Southeast Asia Earth Sci.
(1994) - et al.
Tectonic evolution of the NE margin of the Tibetan Plateau: evidence from the central Longmen Mountains, Sichuan Province, China
J. SE Asian Earth Sci.
(1994) - et al.
The effects of long alpha-stopping distances on (U–Th)/He ages
Geochim. Cosmochim. Acta
(1996) - et al.
Surface deformation related to the 2008 Wenchuan earthquake, and mountain building of the Longmen Shan, eastern Tibetan Plateau
J. Asian Earth Sci.
(2011) - et al.
Estimating the component ages in a finite mixture
Nuclear Tracks Radiation Measurements
(1990)
Cenozoic thermo-tectonic evolution of the Gangdese batholith constrained by low-temperature thermochronology
Gondwana Res.
A natural long-term track annealing experiment for apatite
Nuclear Tracks
Fission track lengths in the apatite annealing zone and the interpretation of mixed ages
Earth Planet. Sci. Lett.
Comparison of zeta calibration baseline for fission track dating of apatite, zircon, and sphene
Chem. Geol.
Thermal annealing of fission tracks in apatite: 1. A qualitative description
Chem. Geol. (Isotope Geosci. Sect.)
Imaging the crustal structure beneath the eastern Tibetan Plateau and implications for the uplift of the Longmen Shan range
Earth Planet. Sci. Lett.
Indosinian deformation of the Songpan Garzê Fold Belt, northeast Tibetan Plateau
J. Struct. Geol.
Standardization of fission track dating calibration: recommendation by the Fission track Working Group of the I.U.G.S
Subcommission Geochronol. Chem. Geol. (Isot. Geosci. Sect.).
The zeta-age calibration of fission track dating
Isot. Geosci.
Structural model of 2008 Mw 7.9 Wenchuan earthquake in the rejuvenated Longmen Shan thrust belt, China
Tectonophysics
Differential late-Cenozoic uplift across the Dongjiu-Milin Fault Zone in the Eastern Himalayan Syntaxis revealed by low-temperature thermochronology
J. Asian Earth Sci.
Spatial variation in Meso-Cenozoic exhumation history of the Longmen Shan thrust belt (eastern Tibetan Plateau) and the adjacent western Sichuan basin: constraints from fission track thermochronology
J. Asian Earth Sci.
Characteristics of the fault-related rocks, fault zones and the principal slip zone in the Wenchuan Earthquake Fault Scientific Drilling Project Hole-1 (WFSD-1)
Tectonophysics
Cenozoic low temperature cooling history of the Northern Tethyan Himalaya in Zedang, SE Tibet and its implications
Tectonophysics
Multiple episodes of fast exhumation since Cretaceous in southeast Tibet, revealed by low-temperature thermochronology
Earth Planet. Sci. Lett.
He diffusion and (U-Th)/He thermochronometry of zircon: initial results from Fish Canyon Tuff and Gold Butte
Tectonophysics
Holocene paleoearthquakes of the Maoergai fault, eastern Tibet
Tectonophysics
Crustal studies in the area of the 2008 Sichuan earthquake from seismologic and gravimetric data
Tectonophysics
Timing of granite emplacement and cooling in the Songpan-Garzê Fold Belt (eastern Tibetan Plateau) with tectonic implications
J. Asian Earth Sci.
The tectonic evolution of the Songpan-Ganzi (North Tibet) and adjacent areas form Proterozoic to present: a synthesis
J. Asian Earth Sci.
Allanite petrochronology in fresh and retrogressed garnet-biotite metapelites from the Longmen Shan (eastern Tibet)
J. Petrol.
The Mesozoic along-strike tectono-metamorphic segmentation of Longmen Shan (eastern Tibetan plateau)
Tectonics
Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica 40Ar/39Ar ages in the Longmen Shan (eastern Tibet)
J. Metamorph. Geol.
The Longriqu fault zone, eastern Tibetan Plateau: segmentation and Holocene behavior
Tectonics
Differential exhumation across the Longriba fault system: implications for the eastern Tibetan Plateau
Tectonics
The continental collision zone, South Island, New Zealand: comparison of geogynamical models and observations
J. Geophys. Res.
Regional Geology of Sichuan Province
Tectonics of the Longmen Shan and adjacent regions, central China
Int. Geol. Rev.
Etude tectonique d'une chaîne de décollement: Tectonique triasique et tertiaire de la chaîne de Songpan-Ganzi (east Tibet): Géometrie et cinématique des déformations dans les prismes d'accrétion sédimentaire: Modélisation analogique
Miocene burial and exhumation of the India-Asia collision zone in southern Tibet: response to slab dynamics and erosion
Geology
Tectonic transition from the Songpan-Garzê fold belt to the Sichuan Basin, south-western China
Basin Res.
Late Cenozoic uplift of southeastern Tibet
Geology
Constraints on Cenozoic tectonics in the southwestern Longmen Shan from low-temperature thermochronology
Lithosphere
Thermal evolution of the Gangdese Batholith, southern Tibet: a history of episodic unroofing
Tectonics
The subsidence of Western Sichuan depression and the rising of Longmenshan
J. Chengdu Coll. Geol.
Survival of ancient landforms in a collisional setting as revealed by combined fission track and (U-Th)/He thermochronometry: a case study from Corsica (France)
J. Geol.
The Mw 7.9, 12 May 2008 Sichuan earthquake rupture measured by sub-pixel correlation of ALOS PALSAR amplitude images
Earth Planets Space
Indosinian progressive deformation and its chronogenesis in Longmengshan structural belt
Oil Gas Geol.
Fission track evidence for rapid uplift of the Eastern Himalayan junction since Pliocene
Chin. Sci. Bull.
Stratigraphic and U-Pb SHRIMP detrital zircon evidence for a Neoproterozoic continental arc, Central China: Rodinia implications
J. Geol.
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