Late Cenozoic Evolution of the Central Longmen Shan, Eastern Tibet: Insight from (U – Th)/He Thermochronometry

Tectonics (Impact Factor: 3.32). 10/2009; 28(5):TC5009. DOI: 10.1029/2008TC002407


This article presents (U-Th)/He thermochronological data from the Longmen Shan belt, eastern Tibet. Located between the Songpan-Garze terrane and the Yangtze craton, this mountain range is one of the steepest margins of the Tibetan Plateau and an important area for the comprehension of the mechanisms that control the dynamics of such plateau borders in terms of spatial distribution of deformation or timing of topographic building. We describe several age-elevation transects and perform forward modeling of our data to derive quantitative information on the exhumation of the range. A major phase of exhumation started at 8–11 Ma, with an average rate of ∼0.65 mm a−1. Comparison of zircon and apatite ages indicates that the eastern part of the range may have experienced a significant decrease in exhumation since 2–3 Ma. We use the distribution of finite exhumation across the major faults of the area to quantify their dip-slip throw rate over the last 10 Ma. The Beichuan Fault, which was activated during the 2008 Sichuan earthquake, is the major active structure of the Longmen Shan since the late Miocene, with an average thrusting slip rate between 0.4 and 1 mm a−1. Conversely, over the same time period, only minor dip-slip activity occurred on the Wenchuan Fault Zone. This distribution in space and time of exhumation and deformation is discussed and compared to the different proposed models for the geodynamical evolution of the eastern Tibetan margin. It also provides an important long-term perspective to put in context the destructive 2008 Sichuan earthquake that struck the central Longmen Shan.

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Available from: Raphaël Pik, Jan 22, 2014
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    • "In the eastern margin of the Tibetan Plateau, thermochronology analysis of zircon and apatite indicated that the denudation rates reached 1e2 mm/y for the Longmen Shan region during the Late Cenozoic (Kirby et al., 2002). Later, long-term denudation rates for the Pengguan Massif and Longmen Shan front measured by low- temperature thermochronology were estimated to be ~0.5e0.7 mm/y (Kirby, 2008; Godard et al., 2009). Recently, shortterm denudation rates in the earthquake region were estimated to vary between 0.2 and 0.3 mm/y, which are measured from concentrations of 10 Be in quartz extracted from river sand prior to the Wenchuan earthquake (Ouimet et al., 2009; Ouimet, 2010). "
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    ABSTRACT: Identifying and understanding the respective influence of climate and tectonic processes becomes a frontier topic in tectonically active mountain ranges. In the eastern Tibetan Plateau, earthquake occurred frequently and usually led to formation of many dammed lakes. In this study, a last deglacial section of lacustrine sediments at Xinmocun in eastern Tibet is selected for conventional X-ray fluorescence (XRF) and Scanning XRF (SXRF) elemental analysis. The high correlation of major and trace element abundances between the Xinmocun lacustrine samples and the loess-soil samples from the Chinese Loess Plateau (CLP) supports the previous view of the eolian origin of the Xinmocun lacustrine sediments. Analysis of major element abundances, ratios and trace element ratios indicates that the dust provenance of the Xinmocun lacustrine sediments is different from that of the CLP, and is similar to that of the loess at Ganzi and Hongyuan nearby the study area. The significant variations of most geochemical elements and their close coupling with grain-size variations can’t be reasonably explained by the changes in transport dynamics of eolian dust, and is possibly caused by the intermittent changes in available dust provenance. Frequent earthquakes usually triggered abundant landslides and provided large amounts of dust for the study area. Accordingly, like the >16 μm fraction of the Xinmocun grain-size record, many element abundances and their ratios, such as SiO2/Al2O3, TiO2/Al2O3, CaO/Al2O3, Sr/Al2O3, Rb/Sr, and Na2O/Al2O3, can be regarded as sensitive indicators of earthquake events in the tectonically active regions. SXRF measurements at the U-channel surface can provide some cost-effective indicators of seismic events, such as Si/Al, Ti/Al, Ca/Al, Sr/Al, Zr/Rb, and Rb/Sr. On the other hand, significant variations in most element abundances and their ratios of the Xinmocun lacustrine sediments correlate closely with those of its grain-size record. They all have no increasing or decreasing trends with time. These suggest that tectonic activities characterized by seismic events possibly had a major role on the landscape erosion in the eastern Tibetan Plateau while the climatic influence seems minor, which needs to be examined in the future.
    Quaternary International 08/2015; DOI:10.1016/j.quaint.2015.07.037 · 2.06 Impact Factor
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    • "Since Late Triassic, the block experienced extensive crustal deformation following the convergence between the Indian and Eurasian plates (e.g. Wang and Shi, 1982; Xiao et al., 2007) and is considered as a window to continental collision, uplift and plateau growth (Maddox, 1984; Kirby et al., 2002; Godard et al., 2009; Li et al., 2012). This region has been in the focus of several investigations based on geological and geophysical techniques. "
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    ABSTRACT: Following the 2008 Mw 7.9 Wenchuan and 2013 Ms 7.0 Lushan earthquakes, the Longmenshan thrust-fault belt and the Songpan–Ganzi terrane have been the focus of several investigations. Here we use the H–k stacking technique and neighborhood algorithm to investigate the seismic structure of this area. Based on the presence of felsic lower crust and the Mesozoic crustal architecture of the Songpan–Ganzi and Longmenshan area, we exclude the model on the eastward flow of the middle and lower crust assigned as the cause for the crustal thickening in previous studies. In contrast, the E–W trending cumulative compression induced by the continued northward motion of the Indian plate and India-Asian collision are identified as the dominant factors leading to the crustal thickening in the Longmenshan thrust-fault region as well as the Songpan–Ganzi terrane. Particularly, the 2008 Mw 7.9 Wenchuan and 2013 Ms 7.0 Lushan earthquakes likely indicate the cumulative offsets and the E–W continuing compression.
    Journal of Asian Earth Sciences 12/2014; 96:226–236. DOI:10.1016/j.jseaes.2014.09.026 · 2.74 Impact Factor
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    • "Zircon grains (prismatic to round-shaped, 0 to 2 pyramids, with an equivalent spherical radius ranging from 35 to 60 μm) were then measured, and loaded in Pt capsules for He extraction at CRPG. They were outgassed at 1500 • C for 20 min, and analyzed for He concentrations with a VG603 noble gas mass spectrometer (Pik et al., 2003; Godard et al., 2009). After total helium extraction, Pt capsules containing zircon grains were retrieved for U, Th, and Sm content measurements at SARM (Nancy, France). "
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    ABSTRACT: thermal inheritance detrital thermochronology margin inversion inverse modeling Pyrenees The extent to which heat recorded in orogens reflects thermal conditions inherited from previous rift-related processes is still debated and poorly documented. As a case study, we examine the Mauléon basin in the north-western Pyrenees that experienced both extreme crustal thinning and tectonic inversion within a period of ∼30 Myrs. To constrain the time–temperature history of the basin in such a scenario, we provide new detrital zircon fission-track and (U–Th–Sm)/He thermochronology data. The role of rift-related processes in subsequent collision is captured by inverse modeling of our thermochronological data, using relationships between zircon (U–Th–Sm)/He ages and uranium content, combined with thermo-kinematic models of a rift-orogen cycle. We show that the basin recorded significant heating at about 100 Ma characterized by high geothermal gradients (∼80 • C/km). Our thermo-kinematic modeling and geological constraints support the view that subcontinental lithospheric mantle was exhumed at that time below the Mauléon basin. Such a high geothermal gradient lasted 30 Myr after onset of convergence at ∼83 Ma and was relaxed during the collision phase from ∼50 Ma. This study suggests that heat needed for ductile shortening during convergence, is primarily inherited from extension rather than being only related to tectonic and/or sedimentary burial. This should have strong implications on tectonic reconstructions in many collision belts that resulted from inversion of hyper-extended rift basins.
    Earth and Planetary Science Letters 10/2014; 408:296-306. DOI:10.1016/j.epsl.2014.10.014 · 4.73 Impact Factor
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