There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan-Maowen, B...There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan-Maowen, Beichuan-Yingxiu and Pengxian-Guanxian faults, terrace offsets, scarps, fault-controlled saddles, dextral shutter ridges, dextral channel offsets, graben, shatter belts, and pull-apart basins. Electron spin resonance （ESR） and thermoluminescence（TL） ages were obtained using silty sand taken from below the surface of the sediments. According to these data, we calculated the rates of thrusting and strike-slip, and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike-slipping less than 1.46 mm/a. The Longmen Shan is a zone of NNE-trending dextral shear with slip-dip ratio of 6：1-1.3：1. From NW to SE, the thrust component becomes smaller, whereas the strike-slip component becomes larger.展开更多
Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been pr...Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be展开更多
浅源地震是山区地壳抬升的主要驱动力（Avouac，2008）。然而，浅源大地震也触发大范围的同震滑坡，造成显著、但在空间上不均匀的侵蚀（Keefer，1994；Malamud et al，2004；Larsen et al，2010）。因此地壳抬升与同震滑坡的分布及规...浅源地震是山区地壳抬升的主要驱动力（Avouac，2008）。然而，浅源大地震也触发大范围的同震滑坡，造成显著、但在空间上不均匀的侵蚀（Keefer，1994；Malamud et al，2004；Larsen et al，2010）。因此地壳抬升与同震滑坡的分布及规模间的相互作用就引发了一个根本的问题，即大地震及其相关的滑坡是创生还是消毁了山区地形。2008年中国四川Mw7．9汶川地震触发了超过56000处滑坡（Dai et al，2011），其空间分布仅仅部分与构造变形样式有关（Shen et al，2009）。通过将滑坡面积一体积标度关系（Larsen et al，2010；Guzzetti et al，2009）应用于高分辨率卫星影像，我们仔细检查了造山方量的潜在变化。我们估计，同震滑坡产生了约5～15km^3的可侵蚀物质，大于2．6±1．2km^3（deMichele et al，2010）的同震地壳抬升净方量。这种差异表明，在可能的2000-4000年的地震复发周期中（Shen et al，2009），即使只有小部分滑坡物质从造山带中运移走，汶川地震也会在龙门山导致物质净亏损。我们的结果对长期以来广泛持有的大倾滑或走滑地震能造山的观点提出了挑战，并希望引起对同震滑移、滑坡量与地形生成之间的关系更多的思考研究。展开更多
基金This research was supported by the National Nature Foundation of China （49803031, 40372084） the Seismic Scientific United Fund （95-07-0425）+3 种基金 US National Science Foundation grant EAR-0125565 ETH Forschungskommission grant TH-4/03-01 Key Subject Program of Sichuan province Grant No. SZD0408 and the Program for the Subject of Ph.D. in Higher Education Institute, Grant No.20050616004.
文摘There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan-Maowen, Beichuan-Yingxiu and Pengxian-Guanxian faults, terrace offsets, scarps, fault-controlled saddles, dextral shutter ridges, dextral channel offsets, graben, shatter belts, and pull-apart basins. Electron spin resonance （ESR） and thermoluminescence（TL） ages were obtained using silty sand taken from below the surface of the sediments. According to these data, we calculated the rates of thrusting and strike-slip, and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike-slipping less than 1.46 mm/a. The Longmen Shan is a zone of NNE-trending dextral shear with slip-dip ratio of 6：1-1.3：1. From NW to SE, the thrust component becomes smaller, whereas the strike-slip component becomes larger.
基金supported by the China National Natural Science Foundation (Grant No. 40841010,40972083,41172162)CGS Foundation (Grant No.1212011121268)Foundation from State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Grant No. SK-0801)
文摘Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be
文摘浅源地震是山区地壳抬升的主要驱动力（Avouac，2008）。然而，浅源大地震也触发大范围的同震滑坡，造成显著、但在空间上不均匀的侵蚀（Keefer，1994；Malamud et al，2004；Larsen et al，2010）。因此地壳抬升与同震滑坡的分布及规模间的相互作用就引发了一个根本的问题，即大地震及其相关的滑坡是创生还是消毁了山区地形。2008年中国四川Mw7．9汶川地震触发了超过56000处滑坡（Dai et al，2011），其空间分布仅仅部分与构造变形样式有关（Shen et al，2009）。通过将滑坡面积一体积标度关系（Larsen et al，2010；Guzzetti et al，2009）应用于高分辨率卫星影像，我们仔细检查了造山方量的潜在变化。我们估计，同震滑坡产生了约5～15km^3的可侵蚀物质，大于2．6±1．2km^3（deMichele et al，2010）的同震地壳抬升净方量。这种差异表明，在可能的2000-4000年的地震复发周期中（Shen et al，2009），即使只有小部分滑坡物质从造山带中运移走，汶川地震也会在龙门山导致物质净亏损。我们的结果对长期以来广泛持有的大倾滑或走滑地震能造山的观点提出了挑战，并希望引起对同震滑移、滑坡量与地形生成之间的关系更多的思考研究。
