|
青藏高原东部地壳上地幔S波速度结构——下地壳流的深部环境
摘要
在青藏高原东部沿30°N布设由26个台站组成的远震观测剖面.用远震P波接收函数反演方法获得了该剖面下方0~80km深度范围的S波速度结构.反演的结果揭示了沿剖面不同构造块体的地壳速度结构横向变化特征.从喜马拉雅东构造结北侧的林芝,往东北方向的地壳逐渐增厚;地壳厚度在班公-怒江缝合带为最大值,达72km;进入羌塘地块,减至65km;至巴颜喀拉地块,为57~64km;至四川盆地,仅为40~45km.剖面的巴塘以东部分与2000年完成的竹巴龙-资中人工地震测深剖面重合,由远震接收函数确定的S波地壳结构与由人工地震测深获得的P波地壳结构在莫霍界面和壳内主要界面的深度上有很好的一致性.在羌塘地块和巴颜喀拉地块,沿观测剖面的下地壳(30~60km深度范围内)普遍存在低速异常,而四川盆地下地壳则属于正常的速度分布.剖面通过的各构造单元地壳平均波速比(泊松比):拉萨地块1.73(σ=0.247),班公-怒江缝合带1.78(σ=0.269),羌塘地块1.80(σ=0.275),巴颜喀拉地块1.86(σ=0.294)和扬子地块1.77(σ=0.265).羌塘地块和巴颜喀拉地块具有下地壳S波低速异常、复杂的莫霍过渡带以及地壳高泊松比的特征,预示下地壳物质处于热和软弱状态,这是青藏高原东部存在下地壳流的深部环境.下地壳韧性物质的流动可能起因于从高原内部至外部上地壳内重力势能的变化.
引文
1Langston C A.Structure under Mount Rainier,Washington,inferred from teleseismic body waves.J Geophys Res,1979,84(9):4749—4762
2Owens T J,Zandt G,Taylor S R.Seismic evidence for an ancient rift beneath the Cumberland Plateau,Tennessee:a detailed analysis of broadband teleseismic P waveforms.J Geophys Res,1984,89:7783—7795 3Zhu L,Owens T J,Randall G E.Lateral variation in crustal structure of the northern Tibetan Plateau inferred from teleseismic re-ceiver functions.Bull Seism Soc Am,1995,85(6):1531—1540 4Kind R,Ni J,Zhao W,et al.Evidence from earthquake data for a partially molten crustal layer in southern Tibet.Science,1996,274:1692—1694 5Yuan X,Ni J,Kind R,et al.Lithospheric and upper mantle structure of southern Tibet from a seismological passive source experi-ment.J Geophys Res,1997,102(B12):27491—27500 6刘启元,Kind R,李顺成.中国数字地震台网的接收函数及其非线性反演.地球物理学报,1997,40(3):356—368 7Kosarev G,Kind R,Sobolev S V,et al.Seismic evidence for a detached Indian lithospheric mantle beneath Tibet.Science,1999,283:1306—1309 8Vergne J,Wittlinger G,Qiang H,et al.Seismic evidence for stepwise thickening of the crust across the NE Tibetan Plateau.Earth Planet Sci Lett,2002,203:25—33 9Li X,Kind R,Yuan X,et al.Rejuvenation of the lithosphere by the Hawaiian plume.Nature,2004,427:827—829,doi:10,1038/nature02349 10Ai Y,Zheng T,Xu W,et al.A complex660km discontinuity beneath northeast China.Earth Planet Sci Lett,2003,212:63—71 11吴庆举,曾融生.用宽频带远震接收函数研究青藏高原的地壳结构.地球物理学报,1998,41:669—679 12陈九辉,刘启元,李顺成,等.青藏高原东北缘-鄂尔多斯地块地壳上地幔S波速度结构.地球物理学报,2005,48:333—342 13Shi D,Zhao W J,Brown L,et al.Detection of southward intracontinental subduction of Tibetan lithosphere along the Ban-gong-Nujiang suture by P-to-S converted waves.Geology,2004,32:209—212,doi:10,1130/G19814.1 14Burchfiel B C,Chen Z,Liu Y,et al.Tectonics of Longmen Shan and adjacent regions,Central China.Int Geol Rev,1995,37:661—736 15King R W,Shen F,Burchfiel B C,et al.Geodetic measurement of crustal motion in southwest China.Geology,1997,25:179—182 16俞如龙,郝子文,侯立玮.川西高原中新生代碰撞造山带的大地构造演化.四川地质学报,1989,9:1—9 17许志琴,侯立玮,王宗秀,等.中国松潘-甘孜造山带的造山过程.北京:地质出版社,1992.1—60 18四川省地震局.鲜水河活动断裂带.成都:四川科学技术出版社,1989 19汪一鹏.青藏高原活动构造基本特征.见:马宗晋,汪一鹏,张燕平,主编.青藏高原岩石圈现今变动与动力学.北京:地震出版社,2001.251—262 20尹安.喜马拉雅-青藏高原造山带地质演化—显生宙亚洲大陆生长.地球学报,2001,22:193—230 21Tapponnier P,Peltzer G,Dain L,et al.Propagating extrusion tectonics in Asia:new insights from simple experiments with plasticine.Geology,1982,10:611—616 22Tapponnier P,Peltzer G,Armijo R.On the mechanics of the collision between India and Asia.In:Coward M P,Ries A C,eds.Colli-sion Tectonics.London:Geol Soc Spec Publ19,1986.115—157 23陈学波,吴跃强,杜平山,等.龙门山构造带两侧速度结构特征.见:国家地震局科技监测司,编.中国大陆深部构造的研究与进展.北京:地质出版社,1986.97—113 24李立,金国元.攀西裂谷及龙门山断裂带地壳上地幔大地电磁测深研究.物探与化探,1987,11:161—169 25崔作舟,陈纪平,吴苓.花石峡-邵阳深部地壳的结构和构造.北京:地质出版社,1996.49—168 26曾融生,朱介寿,周兵,等.西藏高原及其东部邻区的三维地震波速度结构与大陆碰撞模型.地震学报,1992,14(增刊):523—533 27刘建华,刘福田,吴华,等.南北地震带的地壳上地幔三维速度结构.地球物理学报,1989,32:143—152 28Huang J,Zhao D,Zheng S.Lithospheric structure and its relationship to seismic and volcanic activity in southwest China.J Geophys Res,2002,107(B10).doi:10.1029/2000JB000137 29Wang C Y,Chan W W,Mooney W D.3-D velocity structure of crust and upper mantle in southwestern China and its tectonic impli-cations.J Geophys Res,2003,108(B9):2442,doi:10.1029/2002JB001973 30李勇,徐公达,周荣军,等.龙门山均衡重力异常及其对青藏高原东缘山脉地壳隆升的约束.地质通报,2005,24:1162—1168 31王椿镛,吴建平,楼海,等.青藏高原东缘的地壳P波速度结构.中国科学D辑:地球科学,2002,33(增刊):181—189 32Wang C Y,Han W B,Wu J P,et al.Crustal structure beneath the eastern margin of the Tibetan plateau and its tectonic implications.J Geophys Res,2007,112:B07307,doi:10.1029/2005JB003873 33Yao H,van der Hilst R D,De Hoop M V.Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis,I-phase velocity maps.Geophys J Int,2006,166:732—744 34苏伟,彭艳菊,郑月军,等.青藏高原及其邻区地壳上地幔S波速度结构.地球学报,2002,23(3):193—200 35Rapine R,Tillman F,West M,et al.Crustal structure of northern and southern Tibet from surface wave dispersion analysis.J Geophys Res,2003,108(B2),2120,doi:10,1029/2001JB0000445 36Kennett B L N.Seismic Wave Propagation in Stratified Media.London:Cambridge University Press,1981 37Randall G E.Efficient calculation of differential seismograms for lithospheric receiver functions.Geophys J Int,1989,99(2):469—481 38Zhu L,Kanamori H.Moho depth variation in southern California from teleseismic receiver functions.J Geophys Res,2000,105(B2):2969—2980 39赵文津,赵逊,史大年,等.喜马拉雅和青藏高原深剖面(INDEPTH)研究进展.地质通报,2002,22(11):691—700 40许志琴,李海兵,杨经绥.造山的高原-青藏高原巨型造山拼贴体和造山类型.地学前缘,2006,13(4):1—17 41Christensen N I.Poisson’s ratio and crustal seismology.J Geophys Res,1996,101:3139—3156 42Owens T J,Zandt G.Implications of crustal property variations for model of Tibetan Plateau evolution.Nature,1997,387:37—43 43Kind R,Yuan X,Saul J,et al.Seismic images of crust and upper mantle beneath Tibet:evidence for Eurasian plate subduction.Sci-ence,2002,298:1219—1221 44Zandt G,Myers S C,Wallace T C.Crust and mantle structure across the Basin and Range-Colorado plateau boundary at37°N latitude and implications for Cenozoic extensional mechanism.J Geophys Res,1995,100:10529—10548 45Chen,Z,Burchfiel B C,Liu Y,et al.Global positioning system measurements from eastern Tibet and their implications for In-dia/Eurasia intercontinental deformation.J Geophys Res,2000,105(B7):16215—16227 46Royden L H,Burchfiel B C,King R W,et al.Surface deformation and lower crustal flow in eastern Tibet.Science,1997,276:788—790 47Klemperer S L.Crustal flow in Tibet:geological evidence for the physical state of Tibetan lithosphere.In:Searle M P,Law R D,eds.Channel Flow,Ductile Extrusion and Exhumation of Lower Mid-Crust in Continental Collision Zones.London:Geol Soc Spec Pub,2006.39—70 48Meisnner R,Tilmann F,Haines S.About the lithospheric structure of central Tibet,based on seismic data from the INDEPTHⅢprofile.Tectonophys,2004,380:1—25 49Zhang Z J,Klemperer S L.West-east variation in crustal thickness in northern Lhasa block,central Tibet,from deep seismic sounding data.J Geophys Res,2005,110:B09403,doi:10.1029/2004/2004JB003139 50Flesch L M,Holt W E,Silver P G,et al.Constraining the extent of crust-mantle coupling in central Asia using GPS,geologic,and shear-wave splitting data.Earth Planet Sci Lett,2005,238:248—268 |