青藏高原东缘岩石圈结构对现今地表垂向运动影响的数值分析
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摘要
参考青藏高原东缘松潘—甘孜地块至四川盆地陡变地形起伏和地壳密度结构的横向差异,本文建立了二维牛顿黏性流体有限元模型,计算分析构造加载、陡变地形和重力效应控制下青藏高原东缘岩石圈变形特征,探讨横向不均匀的地壳密度结构、陡变地形和岩石圈流变性质对区域现今垂向运动的影响.计算结果显示:在构造加载作用下,松潘—甘孜地块至四川盆地地表抬升微弱.区域横向不均匀的地壳密度结构驱使松潘—甘孜地块地壳整体抬升,速率高达2mm·a~(-1),四川盆地整体下沉,速率约1mm·a-1,与龙门山两侧现今观测到的地表垂向变形模式相近.龙门山地区陡变地形驱使柔性地壳流动,调整区域地壳局部变形;岩石圈流变结构影响重力驱动作用下的模型变形量值和岩石圈变形耦合程度,松潘—甘孜地块较低的中地壳黏滞系数引起上、下地壳的变形解耦;模型较高的岩石圈地幔黏滞系数使重力驱动作用下区域垂向变形量降低.因此,青藏高原东缘地壳密度结构差异、地形起伏和岩石圈流变性质是现今区域垂向变形的重要动力学控制因素.
Based on the steep topography and pronounced contrast in crustal densities from Songpan-Garzêblock to Sichuan basin in Eastern Tibet,we set up a 2-D finite element model using the Newton viscous constitutive equations,to quantitatively analyze the lithospheric deformation in Eastern Tibet driven by tectonic loading,steep topographic relief and regional gravity.We further discuss the influences of the lateral heterogeneity in crustal density,topography relief and lithospheric rheology on regional vertical movements.The numerical results show that:The tectonic loading induces slight vertical uplift from Songpan-Garzêblock to Sichuan basin,while the gravity adjustment due to lateral heterogeneity of crustal density leads to whole-scale uplift up to 2 mm·a~(-1) in Songpan-Garzêblock,and surface subsidence of ～1 mm·a~(-1) in Sichuan basin,with the deforming pattern similar to the observed vertical movements.The steep topography in Longmenshan region induces pronounced ductile crustal flow,and adjusts the local crustal deformation.The lithospheric rheology affects the regional deformation and coupling extent between each layer of the lithosphere,with lower viscosity of middle crust leading to decoupling deformation in the Songpan-Garzêblock,and higher viscosity of the lithospheric mantle inducing less vertical movements driven by regional gravity effect.Therefore,the lateral heterogeneity of crustal density,topography relief and rheology of the lithosphere are the significant controlling factors for regional vertical movements in Eastern Tibet.
Based on the steep topography and pronounced contrast in crustal densities from Songpan-Garzêblock to Sichuan basin in Eastern Tibet,we set up a 2-D finite element model using the Newton viscous constitutive equations,to quantitatively analyze the lithospheric deformation in Eastern Tibet driven by tectonic loading,steep topographic relief and regional gravity.We further discuss the influences of the lateral heterogeneity in crustal density,topography relief and lithospheric rheology on regional vertical movements.The numerical results show that:The tectonic loading induces slight vertical uplift from Songpan-Garzêblock to Sichuan basin,while the gravity adjustment due to lateral heterogeneity of crustal density leads to whole-scale uplift up to 2 mm·a~(-1) in Songpan-Garzêblock,and surface subsidence of ～1 mm·a~(-1) in Sichuan basin,with the deforming pattern similar to the observed vertical movements.The steep topography in Longmenshan region induces pronounced ductile crustal flow,and adjusts the local crustal deformation.The lithospheric rheology affects the regional deformation and coupling extent between each layer of the lithosphere,with lower viscosity of middle crust leading to decoupling deformation in the Songpan-Garzêblock,and higher viscosity of the lithospheric mantle inducing less vertical movements driven by regional gravity effect.Therefore,the lateral heterogeneity of crustal density,topography relief and rheology of the lithosphere are the significant controlling factors for regional vertical movements in Eastern Tibet.
引文
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.
Bendick R,Flesch L.2007.Reconciling lithospheric deformation and lower crustal flow beneath central Tibet.Geology,35(10):895-898.
Bird P.1991.Lateral extrusion of lower crust from under high topography in the isostatic limit.Journal of Geophysical Research:Solid Earth,96(B6):10275-10286.
Bürgmann R,Dresen G.2008.Rheology of the lower crust and upper mantle:Evidence from rock mechanics,geodesy,and field observations.Annual Review of Earth and Planetary Sciences,36:531-567.
Burchfiel B C,Chen Z L,Liu Y,et al.1995.Tectonics of the Longmen Shan and adjacent regions,central China.International Geology Review,37(8):661-735.
Burchfiel B C.2004.2003Presidential address:New technology,new geological challenges.GSA Today,14:4-9.
Chen S,Xu W M,Shi L,et al.2013.Gravity field and lithospheric mechanical properties of Longmenshan fault zone and its surrounding areas.Acta Seismologica Sinica(in Chinese),35(5):692-703.
Clark M K,Royden L H.2000.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow.Geology,28(8):703-706.
Copley A.2008.Kinematics and dynamics of the southeastern margin of the Tibetan Plateau.Geophysical Journal International,174(3):1081-1100.
Deng Q D,Chen S F,Zhao X L.1994.Tectonics,seismicity and dynamics of Longmenshan mountains and its adjacent regions.Seismology and Geology(in Chinese),16(4):389-403.
England P,Houseman G.1986.Finite strain calculations of continental deformation:2.Comparison with the India-Asia collision zone.Journal of Geophysical Research:Solid Earth,91(B3):3664-3676.
Fu G Y,Gao S H,Freymueller J T,et al.2014.Bouguer gravity anomaly and isostasy at western Sichuan Basin revealed by new gravity surveys.Journal of Geophysical Research:Solid Earth,119(4):3925-3938.
Hao M,Wang Q L,Shen Z K,et al.2014.Present day crustal vertical movement inferred from precise leveling data in eastern margin of Tibetan Plateau.Tectonophysics,632:281-292.
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.
Liang S M,Gan W J,Shen C Z,et al.2013.Three-dimensional velocity field of present-day crustal motion of the Tibetan Plateau derived from GPS measurements.Journal of Geophysical Research:Solid Earth,118(10):5722-5732.
Liang X F,Sandvol E,Chen J,et al.2012.A complex Tibetan upper mantle:A fragmented Indian slab and no south-verging subduction of Eurasian lithosphere.Earth and Planetary Science Letters,333-334:101-111.
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.
Lou H,Wang C Y,Yao Z X,et al.2010.Subsection feature of the deep structure and material properties of Longmenshan fault zone.Earth Science Frontiers(in Chinese),17(5):128-141.
Molnar P,Tapponnier P.1975.Cenozoic tectonics of Asia:Effects of a continental collision.Science,189(4201):419-426.
Pang Y J,Zhang H,Gerya T V,et al.2018.The mechanism and dynamics of N-S rifting in southern Tibet:insight From 3-Dthermomechanical modeling.Journal of Geophysical Research:Solid Earth,123(1):859-877.
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.
Shen X Z.2013.An analysis of the deformation of the crust and LAB beneath the Lushan and Wenchuan earthquakes in Sichuan province.Chinese Journal of Geophysics(in Chinese),56(6):1895-1903,doi:10.6038/cjg20130612.
Shen X Z,Yuan X H,Liu M.2015.Is the Asian lithosphere underthrusting beneath northeastern Tibetan Plateau?Insights from seismic receiver functions.Earth and Planetary Science Letters,428:172-180.
Shen Z K,LüJ N,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau.Journal of Geophysical Research:Solid Earth,110(B11):B11409,doi:10.1029/2004JB003421.
Song C K,Ni Z,Su S P,et al.2017.The relationship between anomalies variation of lithosphere magnetic field and structure of lithosphere magnetic.Journal of Seismological Research(in Chinese),2017,40(3):357-361.
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,Han W B,Wu J P,et al.2007.Crustal structure beneath the eastern margin of the Tibetan Plateau and its tectonic implications.Journal of Geophysical Research:Solid Earth,112(B7):B07307,doi:10.1029/2005JB003873.
Wang C Y,Lou H,LüZ Y,et al.2008.S-wave crustal and upper mantle′s velocity structure in the eastern Tibetan PlateauDeep environment of lower crustal flow.Science in China Series D:Earth Sciences,51(2):263-274.
Wang E Q,Meng Q R.2008.Mesozoic and Cenozoic tectonic evolution of the Longmenshan fault belt.Science in China Series D:Earth Sciences,52(5):579-592.
Wang Q,Qiao X J,Lan Q G,et al.2011.Rupture of deep faults in the 2008 Wenchuan earthquake and uplift of the Longmen Shan.Nature Geoscience,4(9):634-640.
Wang X,Chen L,Ai Y S,et al.2018.Crustal structure and deformation beneath eastern and northeastern Tibet revealed by P-wave receiver functions.Earth and Planetary Science Letters,497:69-79.
Yi S,Freymueller J T,Sun W K.2016.How fast is the middle lower crust flowing in eastern Tibet?A constraint from geodetic observations.Journal of Geophysical Research:Solid Earth,121(9):6903-6915.
Zhang P Z.2013.A review on active tectonics and deep crustal processes of the Western Sichuan region,eastern margin of the Tibetan Plateau.Tectonophysics,584:7-22.
Zhang Y Q,Teng J W,Wang Q S,et al.2014.Density structure and isostatic state of the crust in the Longmenshan and adjacent areas.Tectonophysics,619-620:51-57.
Zhang Z J,Yuan X H,Chen Y,et al.2010.Seismic signature of the collision between the east Tibetan escape flow and the Sichuan Basin.Earth and Planetary Science Letters,292(3-4):254-264.
陈石,徐伟民,石磊等.2013.龙门山断裂带及其周边地区重力场和岩石层力学特性研究.地震学报,35(5):692-703.
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.
嘉世旭,刘保金,徐朝繁等.2014.龙门山中段及两侧地壳结构与汶川地震构造.中国科学:地球科学,44(3):497-509.
楼海,王椿镛,姚志祥等.2010.龙门山断裂带深部构造和物性分布的分段特征.地学前缘,17(5):128-141.
沈旭章.2013.四川芦山7.0地震和汶川8.0地震震源区地壳岩石圈变形特征分析.地球物理学报,56(6):1895-1903,doi:10.6038/cjg20130612.
宋成科,倪喆,苏树朋等.2017.岩石圈磁场异常变化与岩石圈结构的关系,地震研究,2017,40(3):357-361.
王二七,孟庆任.2008.对龙门山中生代和新生代构造演化的讨论.中国科学D辑:地球科学,38(10):1221-1233.本文编辑胡素芳
Bendick R,Flesch L.2007.Reconciling lithospheric deformation and lower crustal flow beneath central Tibet.Geology,35(10):895-898.
Bird P.1991.Lateral extrusion of lower crust from under high topography in the isostatic limit.Journal of Geophysical Research:Solid Earth,96(B6):10275-10286.
Bürgmann R,Dresen G.2008.Rheology of the lower crust and upper mantle:Evidence from rock mechanics,geodesy,and field observations.Annual Review of Earth and Planetary Sciences,36:531-567.
Burchfiel B C,Chen Z L,Liu Y,et al.1995.Tectonics of the Longmen Shan and adjacent regions,central China.International Geology Review,37(8):661-735.
Burchfiel B C.2004.2003Presidential address:New technology,new geological challenges.GSA Today,14:4-9.
Chen S,Xu W M,Shi L,et al.2013.Gravity field and lithospheric mechanical properties of Longmenshan fault zone and its surrounding areas.Acta Seismologica Sinica(in Chinese),35(5):692-703.
Clark M K,Royden L H.2000.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow.Geology,28(8):703-706.
Copley A.2008.Kinematics and dynamics of the southeastern margin of the Tibetan Plateau.Geophysical Journal International,174(3):1081-1100.
Deng Q D,Chen S F,Zhao X L.1994.Tectonics,seismicity and dynamics of Longmenshan mountains and its adjacent regions.Seismology and Geology(in Chinese),16(4):389-403.
England P,Houseman G.1986.Finite strain calculations of continental deformation:2.Comparison with the India-Asia collision zone.Journal of Geophysical Research:Solid Earth,91(B3):3664-3676.
Fu G Y,Gao S H,Freymueller J T,et al.2014.Bouguer gravity anomaly and isostasy at western Sichuan Basin revealed by new gravity surveys.Journal of Geophysical Research:Solid Earth,119(4):3925-3938.
Hao M,Wang Q L,Shen Z K,et al.2014.Present day crustal vertical movement inferred from precise leveling data in eastern margin of Tibetan Plateau.Tectonophysics,632:281-292.
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.
Liang S M,Gan W J,Shen C Z,et al.2013.Three-dimensional velocity field of present-day crustal motion of the Tibetan Plateau derived from GPS measurements.Journal of Geophysical Research:Solid Earth,118(10):5722-5732.
Liang X F,Sandvol E,Chen J,et al.2012.A complex Tibetan upper mantle:A fragmented Indian slab and no south-verging subduction of Eurasian lithosphere.Earth and Planetary Science Letters,333-334:101-111.
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.
Lou H,Wang C Y,Yao Z X,et al.2010.Subsection feature of the deep structure and material properties of Longmenshan fault zone.Earth Science Frontiers(in Chinese),17(5):128-141.
Molnar P,Tapponnier P.1975.Cenozoic tectonics of Asia:Effects of a continental collision.Science,189(4201):419-426.
Pang Y J,Zhang H,Gerya T V,et al.2018.The mechanism and dynamics of N-S rifting in southern Tibet:insight From 3-Dthermomechanical modeling.Journal of Geophysical Research:Solid Earth,123(1):859-877.
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.
Shen X Z.2013.An analysis of the deformation of the crust and LAB beneath the Lushan and Wenchuan earthquakes in Sichuan province.Chinese Journal of Geophysics(in Chinese),56(6):1895-1903,doi:10.6038/cjg20130612.
Shen X Z,Yuan X H,Liu M.2015.Is the Asian lithosphere underthrusting beneath northeastern Tibetan Plateau?Insights from seismic receiver functions.Earth and Planetary Science Letters,428:172-180.
Shen Z K,LüJ N,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau.Journal of Geophysical Research:Solid Earth,110(B11):B11409,doi:10.1029/2004JB003421.
Song C K,Ni Z,Su S P,et al.2017.The relationship between anomalies variation of lithosphere magnetic field and structure of lithosphere magnetic.Journal of Seismological Research(in Chinese),2017,40(3):357-361.
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,Han W B,Wu J P,et al.2007.Crustal structure beneath the eastern margin of the Tibetan Plateau and its tectonic implications.Journal of Geophysical Research:Solid Earth,112(B7):B07307,doi:10.1029/2005JB003873.
Wang C Y,Lou H,LüZ Y,et al.2008.S-wave crustal and upper mantle′s velocity structure in the eastern Tibetan PlateauDeep environment of lower crustal flow.Science in China Series D:Earth Sciences,51(2):263-274.
Wang E Q,Meng Q R.2008.Mesozoic and Cenozoic tectonic evolution of the Longmenshan fault belt.Science in China Series D:Earth Sciences,52(5):579-592.
Wang Q,Qiao X J,Lan Q G,et al.2011.Rupture of deep faults in the 2008 Wenchuan earthquake and uplift of the Longmen Shan.Nature Geoscience,4(9):634-640.
Wang X,Chen L,Ai Y S,et al.2018.Crustal structure and deformation beneath eastern and northeastern Tibet revealed by P-wave receiver functions.Earth and Planetary Science Letters,497:69-79.
Yi S,Freymueller J T,Sun W K.2016.How fast is the middle lower crust flowing in eastern Tibet?A constraint from geodetic observations.Journal of Geophysical Research:Solid Earth,121(9):6903-6915.
Zhang P Z.2013.A review on active tectonics and deep crustal processes of the Western Sichuan region,eastern margin of the Tibetan Plateau.Tectonophysics,584:7-22.
Zhang Y Q,Teng J W,Wang Q S,et al.2014.Density structure and isostatic state of the crust in the Longmenshan and adjacent areas.Tectonophysics,619-620:51-57.
Zhang Z J,Yuan X H,Chen Y,et al.2010.Seismic signature of the collision between the east Tibetan escape flow and the Sichuan Basin.Earth and Planetary Science Letters,292(3-4):254-264.
陈石,徐伟民,石磊等.2013.龙门山断裂带及其周边地区重力场和岩石层力学特性研究.地震学报,35(5):692-703.
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.
嘉世旭,刘保金,徐朝繁等.2014.龙门山中段及两侧地壳结构与汶川地震构造.中国科学:地球科学,44(3):497-509.
楼海,王椿镛,姚志祥等.2010.龙门山断裂带深部构造和物性分布的分段特征.地学前缘,17(5):128-141.
沈旭章.2013.四川芦山7.0地震和汶川8.0地震震源区地壳岩石圈变形特征分析.地球物理学报,56(6):1895-1903,doi:10.6038/cjg20130612.
宋成科,倪喆,苏树朋等.2017.岩石圈磁场异常变化与岩石圈结构的关系,地震研究,2017,40(3):357-361.
王二七,孟庆任.2008.对龙门山中生代和新生代构造演化的讨论.中国科学D辑:地球科学,38(10):1221-1233.本文编辑胡素芳