ZHANG Xin-Yan,
GAO Rui,
BAI Zhi-Ming et al
.2017.Crustal structure beneath the Longmenshan area in eastern Tibet:new constrains from reprocessing wide-angle seismic data of the Aba-Longmenshan-Suining profile.Chinese Journal Of Geophysics,60(6): 2200-2212,doi: 10.6038/cjg20170614
Crustal structure beneath the Longmenshan area in eastern Tibet:new constrains from reprocessing wide-angle seismic data of the Aba-Longmenshan-Suining profile
ZHANG Xin-Yan1, GAO Rui1,2, BAI Zhi-Ming2,3, XU Tao3,4, LI Qiu-Sheng1
1. Key Laboratory of Earthprobe and Geodynamics, MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China; 2. School of Earth Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; 3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 4. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
Abstract：The Longmenshan area in the eastern Tibetan Plateau experienced strong crustal deformation and faulting during Mesozoic and late Cenozoic epochs resulting in significant uplift of the Longmenshan Mountains, which serves as an important window to see the uplift and lateral expansion of the Tibetan Plateau. In this paper, the deep seismic sounding profile named the Aba-Longmenshan-Suning profile is reprocessed using a high-precision traveltime tomography for velocity structure with an irregular surface to reconstruct the crustal structure beneath this area. The obtained velocity structure along the profile could be divided into three major sections: the Songpan-Garzê block, Longmenshan fault zone and Sichuan basin. The sedimentary cover of the Songpan-Garzê block is about 10 km thick, with high-velocity bodies in 5~10 km depths, which correspond to the faults and likely the intrusion of Mesozoic granites. The undulating interface of the sediment may indicate the thrust-nappe tectonics. Velocity structures of the middle and lower crust change continuously with lower average velocity (about 6.26 km·s-1). In the Sichuan basin, the sediment in the west is thicker than that in the west. The sediment in the west even exhibits compression and torsion forms, which may be caused by compression and erosion. The middle and lower crust in the west is thinner than that in the east with higher average velocity (about 6.29 km·s-1). The Longmenshan fault zone is a transition zone of the crustal velocity and thickness, with the Moho uplifting about 13 km from the west to the east. Along the whole profile the Moho shows toughness winding, while the velocity of the middle and lower crust changes continuously in the lateral direction, which may indicate that the ancient Yangtze block has reached beneath the Songpan-Garzê block. In the Songpan-Garzê block, which is considered to be a passive margin, the middle and lower crust experienced ductile deformation under strong compression. The brittle upper crust with thrust-nappe belts is dragged by the middle and lower crust, while stress is accumulated and released on the faults, which may induce a large number of earthquakes.
Bai D H,Unsworth M J, Meju M A, et al. 2010. Crustal deformation of the eastern Tibetan plateau revealed by magnetotelluric imaging. Nature Geoscience, 3(5): 358-362. Bai Z M, Tian X B, Tian Y. 2011. Upper mantle P-wave tomography across the Longmenshan fault belt from passive-source seismic observations along Aba-Longquanshan profile. Journal of Asian Earth Sciences, 40(4): 873-882. Bruguier O, Lancelot J R, Malavieille J. 1997. U-Pb dating on single detrital zircon grains from the Triassic Songpan-Garzê flysch (Central China): Provenance and tectonic correlations. Earth and Planetary Science Letters, 152(1-4): 217-231. Chen S F, Wilson C J L. 1996. Emplacement of the Longmen Shan thrust-Nappe belt along the eastern margin of the Tibetan Plateau. J. Struct. Geol., 18(4): 413-430. Chen X B, Wu Y Q, Du P S, et al. 1988. Crustal velocity structure at two sides of Longmenshan tectonic belt (in Chinese).//EditDep. of Sci. Program. and Earthquake Monit., China Seismol. Bur., Seismol. In Developments in the Research of Deep Structure of China's Continent, Beijing: Geological Press, 112-127. Chen Z, Burchfiel B C, Liu Y, et al. 2000. Global positioning system measurements from eastern Tibet and their implications for India/Eurasia intercontinental deformation. J. Geophys. Res., 105(B7): 16215-16227. Clark M K, Royden L H. 2000. Topographic ooze: Building the eastern margin of Tibet by lower crustal flow. Geology, 28(8): 703-706. Cook K L, Royden L H. 2008. The role of crustal strength variations in shaping orogenic plateaus, with application to Tibet. J. Geophys. Res., 113(B8): B08407. Cui Z Z, Chen J P, Wu L. 1996. Deep Crustal Structure and Tectonics in Huashixia-Shaoyang Profile (in Chinese). Beijing: Geological Press, 156-168. Deng Q D, Chen S F, Zhao X L. 1994. Tectonics, scismisity and dynamics of Longmenshan mountains and its adjacent regions. Seismology and Geology (in Chinese), 16(4): 389-403. Guo X Y, Gao R, Keller F R, et al. 2013. Imaging the crustal structure beneath the eastern Tibetan Plateau and implications for the uplift of the Longmen Shan range. Earth and Planetary Science Letters, 379: 72-80. Harrowfield M J, Wilson C J L. 2005. Indosinian deformation of the Songpan Garzê Fold Belt, northeast Tibetan Plateau. J. Struct. Geol., 27(1): 101-117. Hobro J W D, Singh S C, Minshull T A. 2003. Three-dimensional tomographic inversion of combined reflection and refraction seismic traveltime data. Geophys. J. Int., 152(1): 79-93. Hole J A. 1992. Nonlinear high-resolution three-dimensional seismic travel time tomography. J. Geophys. Res., 97(B5): 6553-6562. Houseman G, England P. 1993. Crustal thickening versus lateral expulsion in the Indian-Asian continental collision. J. Geophys. Res., 98(B7): 12233-12249, doi: 10.1029/93JB00443. Hubbard J, Shaw J H. 2009. Uplift of the Longmen Shan and Tibetan plateau, and the 2008 Wenchuan (M=7.9) earthquake. Nature, 458(7235): 194-197. Jia S X, Liu B J, Xu Z F, et al. 2014. The crustal structures of the central Longmenshan along and its margins as related to the seismotectonics of the 2008 Wenchuan Earthquake. Science China Earth Sciences, 57(4): 777-790. Lei J S, Zhao D P. 2009. Structural heterogeneity of the Longmenshan fault zone and the mechanism of the 2008 Wenchuan earthquake (Ms8.0). Geochemistry,Geophysics,Geosystems,10(10):Q10010. Li Q S, Gao R, Wang H Y, et al. 2009. Deep background of Wenchuan earthquake and the upper crust structure beneath the Longmen Shan and adjacent areas. Acta Geologica Sinica, 83(4): 733-739. Liu Q Y, van Der Hilst R D, Li Y, et al. 2014. Eastward expansion of the Tibetan Plateau by crustal flow and strain partitioning across faults. Nature Geoscience, 7(5): 361-365, doi: 10.1038/ngeo2130. Ma T, Zhang Z J. 2014. Calculating ray paths for first-arrival travel times using a topography-dependent eikonal equation solver. Bulletin of the Seismological Society of America, 104(3): 1501-1517, doi: 10.1785/0120130172. Meade B J. 2007. Present-day kinematics at the India-Asia collision zone. Geology, 35(1): 81-84. Molnar P, Tapponnier P. 1975. Cenozoic tectonics of Asia: Effects of a continental collision. Science, 189(4201): 419-426, doi: 10.1126/science.189.4201.419. Ren J X, Wang Z X, Chen B W. 1999. Tectonic Maps of China and Its Surrounding Region (in Chinese). Beijing: Geological Press. Royden L H, Burchfiel B C, King R W, et al. 1997. Surface deformation and lower crustal flow in eastern Tibet. Science, 276(5313): 788-790. Royden L H, Burchfiel B C, van der Hilst R D. 2008. The geological evolution of the Tibetan plateau. Science, 321(5892): 1054-1058, doi: 10.1126/science.1155371. Tapponnier P, Xu Z Q, Roger F, et al. 2001. Oblique stepwise rise and growth of the Tibet Plateau. Science, 294(5547): 1671-1677. Wang C Y, Flesch L M, Silver P G, et al. 2008. Evidence for mechanically coupled lithosphere in central Asia and resulting implications. Geology, 36(5): 363-366, doi: 10.1130/G24450A.1. Wang C Y, Han W B, Wu J P, et al. 2003. Crustal structure beneath the Songpan-Garze orogenic belt. Acta Seismologica Sinica (in Chinese), 25(3): 229-241. Wang C Y, Han W B, Wu J P, et al. 2007. Crustal structure beneath the eastern margin of the Tibetan Plateau and its tectonic implications. J. Geophys. Res., 112(B7): B07307. Wang C Y, Wang X L, Shu W, et al. 2006. Seismological evidence of the crust flowing under the eastern boundary part of Qinghai-Tibet Plateau. Earthquake Research in Sichuan (in Chinese),(4):1-4. Wang E C, Meng Q R. 2009. Mesozoic and Cenozoic tectonic evolution of the Longmenshan fault belt. Science in China Series D: Earth Sciences, 52(5): 579-592. Wang X B, Zhu Y T, Zhao X K, et al. 2009. Deep conductivity characteristics of the Longmen Shan, Eastern Qinghai-Tibet Plateau. Chinese J. Geophys. (in Chinese), 52(2): 564-571. Wang Y X, Mooney W D, Han G H, et al. 2005. The crustal P-wave velocity structure from Altyn Tagh to Longmen mountains along the Taiwan-Altay geoscience transect. Chinese J. Geophys. (in Chinese), 48(1): 98-106. Xu T, Li F, Wu Z B, et al. 2014. A successive three-point perturbation method for fast ray tracing in complex 2D and 3D geological models. Tectonophysics, 627: 72-81. Xu T, Xu G M, Gao E G, et al. 2006. Block modeling and segmentally iterative ray tracing in complex 3D media. Geophysics, 71(3): T41-T51. Xu T, Zhang Z J, Gao E, et al. 2010a. Segmentally iterative ray tracing in complex 2D and 3D heterogeneous block models. Bulletin of the Seismological Society of America, 100(2): 841-850. Xu Y, Li Z W, Huang R Q, et al. 2010b. Seismic structure of the Longmen Shan region from S-wave tomography and its relationship with the Wenchuan Ms8.0 earthquake on 12 May 2008, southwestern China. Geophysical Research Letters, 37(2): L02304. Xu Z Q, Ji S C, Li H B, et al. 2008. Uplift of the Longmen Shan range and the Wenchuan earthquake. Episodes, 31(3): 291-301. Zhang X Y, Xu T, Bai Z M, et al. 2017 High-precision reflection traveltime tomography for velocity structure with an irregular surface. Chinese J. Geophys. (in Chinese), 60(2): 541-553, doi: 10.6038/cjg20170209. Zhang Z J, Wang Y H, Chen Y, et al. 2009. Crustal structure across Longmenshan fault belt from passive source seismic profiling. Geophysical Research Letters, 36(17): L17310, doi: 10.1029/2009GL039580. 陈学波,吴跃强,杜平山等. 1988. 龙门山构造带两侧地壳速度结构特征.//国家地震局编.中国大陆深部构造的研究与进展. 北京: 地质出版社, 112-127. 崔作舟, 陈纪平, 吴苓. 1996. 花石峡—邵阳深部地壳的结构和构造. 北京: 地质出版社, 156-168. 邓起东, 陈社发, 赵小麟. 1994. 龙门山及其邻区的构造和地震活动及动力学. 地震地质, 16(4): 389-403. 任纪舜, 王作勋, 陈炳蔚. 1999. 从全球看中国大地构造:中国及邻区大地构造图简要说明. 北京: 地质出版社. 王椿镛, 韩渭宾, 吴建平等. 2003. 松潘—甘孜造山带地壳速度结构. 地震学报, 25(3): 229-241. 王椿镛, 王溪莉, 苏伟等. 2006. 青藏高原东缘下地壳流动的地震学证据. 四川地震, (4): 1-4. 王绪本, 朱迎堂, 赵锡奎等. 2009. 青藏高原东缘龙门山逆冲构造深部电性结构特征. 地球物理学报, 52(2): 564-571. 王有学, Mooney W D, 韩果花等. 2005. 台湾—阿尔泰地学断面阿尔金—龙门山剖面的地壳纵波速度结构. 地球物理学报, 48(1): 98-106. 张新彦, 徐涛, 白志明等. 2017. 起伏地形下的高精度反射波走时层析成像方法. 地球物理学报, 60(2): 541-553, doi: 10.6038/cjg20170209.
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