青藏高原北部新生代火山岩区深部结构特征及其成因探讨
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摘要
青藏高原北部发育的大量新生代钾质、高钾质火山岩体的成因一直是个谜。利用布置在青藏高原内部及其周缘的305个临时宽频地震台站和固定地震台站记录到的9649个远震事件,共139021条P波初至到时资料对青藏高原深部结构特征进行了层析成像反演研究。结果显示,印度岩石圈地幔俯冲前缘已经到达了羌塘地体中部之下,在俯冲前缘存在一个从地幔深处延伸至地表的大规模低速体。该低速体可能是由于印度岩石圈地幔前缘俯冲进入软流圈深处而引起地幔热扰动,造成深部软流圈地幔的热物质向上扩散而形成的深部地幔物质上涌通道;该通道为青藏高原北部的新生代钾质、高钾质火山岩体的形成提供了条件。因此,青藏高原北部新生代火山岩可能是印度岩石圈地幔持续北向俯冲的结果。
There are a lot of Cenozoic potassic and ultrapotassic lavas in the northern Qinghai-Tibet Plateau,their existing is an enigma.We have collected all the available arrival time data recorded by the temporary seismic stations and phase reports from the International Seismological Center in Tibet and its surrounding areas.In the tomographic inversion,we have used 139,021 P-wave arrival times from 9,649 teleseismic events recorded by 305 seismic stations.Tomographic images show that the frontier of the lithospheric mantle of Indian plate(ILM) subducted beneath the center of Qiangtang terrane,and there is a great scale vertical low-velocity zone from deep to surface at the frontier of ILM.It supplies a channel for deep mantle upwelling.Hot materials of deep asthenospheric mantle might flow upward along the channel,then potassic and ultrapotassic lavas erupted in the northern Tibet.Cenozoic potassic and ultrapotassic lavas in the north Tibet are the direct result of northward subducting of ILM.
There are a lot of Cenozoic potassic and ultrapotassic lavas in the northern Qinghai-Tibet Plateau,their existing is an enigma.We have collected all the available arrival time data recorded by the temporary seismic stations and phase reports from the International Seismological Center in Tibet and its surrounding areas.In the tomographic inversion,we have used 139,021 P-wave arrival times from 9,649 teleseismic events recorded by 305 seismic stations.Tomographic images show that the frontier of the lithospheric mantle of Indian plate(ILM) subducted beneath the center of Qiangtang terrane,and there is a great scale vertical low-velocity zone from deep to surface at the frontier of ILM.It supplies a channel for deep mantle upwelling.Hot materials of deep asthenospheric mantle might flow upward along the channel,then potassic and ultrapotassic lavas erupted in the northern Tibet.Cenozoic potassic and ultrapotassic lavas in the north Tibet are the direct result of northward subducting of ILM.
引文
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[26]Pandey O P.Lithospheric mantle deformation beneath the Indiancratons[J].Journal of Geology,1999,107:683-692.
[27]张进,马宗晋.西藏高原西、中、东的分段性及其意义[J].地质学报,2004,78(2):218-227.
[28]滕吉文,尹周勋,刘宏兵,等.青藏高原岩石层三维和二维结构与大陆动力学[J].地球物理学报,1994,37(增刊II):117-130.
[29]张中杰,李英康,王光杰,等.藏北地壳东西向结构与“下凹”莫霍面———来自宽角反射剖面的启示[J].中国科学:D辑,2001,31(11):881-888.
[30]吴建平,曾融生.青藏高原Q值结构反演[J].地震学报,1996,18(2):208-214.
[31]郑洪伟.青藏高原地壳上地幔三维速度结构及其地球动力学意义[D].北京:中国地质科学院,2006.
[32]Owens T J,Zandt G.Implications of crustal property variationsfor models of Tibetan Plateau evolution[J].Nature,1997,387:37-43.
[33]Molnar P.A review of geophysical constraints on the deep struc-ture of the Tibetan Plateau,the Himalaya and the Karakoram,and their tectonic implications[J].The Philosophical Transac-tions of the Royal Society of London,1988,A326:33-88.
[34]Barazangi M,Ni J.Velocities and propagation characteristics ofPn and Sn beneath the Himalayan Arc and Tibetan Plateau:Pos-sible evidence for underthrusting of Indian continental lithospherebeneath Tibet[J].Geology,1982,10:179-185.
[2]肖序常,李廷栋.青藏高原的构造演化与隆升机制[M].广州:广东科技出版社,2000:1-313.
[3]Turner S,Hawk S,Liu J Q,et al.Timing of Tibetan upliftconstrained by analysis of volcanic rocks[J].Nature,1993,364:50-53.
[4]邓万明,郑锡澜,松本征夫.青海可可西里地区新生代火山岩的岩石特征与时代[J].岩石矿物学杂志,1996,15(4):289-298.
[5]Hacker B R,Gnos E,Ratschbacher L,et al.Hot and drydeep crustal xenoliths from Tibet[J].Science,2000,287:2463-2466.
[6]Ding L,Kapp P,Zhong D,et al.Cenozoic volcanism in Ti-bet:Evidence for a transition from oceanic to continental subduc-tion[J].Journal of Petrology,2003,44(10):1833-1865.
[7]Williams H M,Turner S P,Pearce J A,et al.Nature of thesource regions for post-collisional,potassic magmatismin southernand northern Tibet from geochemical variation and inverse traceelement modeling[J].Journal of Petrology,2004,45(3):555-607.
[8]Chung S L,Chu M,Zhang Y,et al.Tibetan tectonic evolutioninferred from spatial and temporal variations in post-collisionalmagmatism[J].Earth Science Reviews,2005,68:173-196.
[9]罗照华,莫宣学,侯增谦,等.青藏高原新生代形成演化的整合模型———来自火成岩的约束[J].地学前缘,2006,13(4):196-211.
[10]Guo Z F,Wilson M,Liu J,et al.Post-collisional,potassicand ultrapotassic magmatism of the Northern Tibetan Plateau:constraints on characteristics of the mantle source,geodynamicsetting and uplift mechanisms[J].Journal of Petrology,2006,47(6):1177-1220.
[11]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[J].地球学报,2001,22(3):193-230.
[12]McNamara D E,Owens T J,Walter W R.Observations of theregional phase propagation in the Tibetan plateau[J].Journalof Geophysics Research,1995,100:22215-22229.
[13]邓万明,孙宏娟,张玉泉.青海囊谦盆地新生代火山岩的K-Ar年龄[J].科学通报,1999,44(20):2554-2558.
[14]邓万明,孙宏娟.青藏北部板内火山岩的同位素地球化学与源区特征[J].地学前缘,1998,5(4):307-317.
[15]迟效国,李才,金巍.藏北羌塘地区新生代火山作用与岩石圈构造演化[J].中国科学:D辑,2005,35(5):399-410.
[16]Zhao D P,Hasegawa A,Horiuchi S.Tomographic Imaging of Pand S wave velocity structure beneath Northeastern Japan[J].Journal of Geophysics Research,1992,97(B13):19909-19928.
[17]Zhao D P,Hasegawa A,Kanamori H.Deep structure of Japansubduction zone as derived from local,regional,and teleseismicevents[J].Journal of Geophysics Research,1994,99(B11):22313-22329.
[18]Wei W B,Unsworth M,Jones A,et al.Detection of wide-spread fluids in the Tibetan crust by magnetotelluric studies[J].Science,2001,292:716-718.
[19]Kao H,R Gao,Ruey-Juin Rau,et al.Co-existence of north-and south-dipping structures beneath the western Tibet-Tarim re-gion[J].Geology,2001,29(7):575-578.
[20]Wittlinger G,Vergne J,Tapponnier P,et al.Teleseismic ima-ging of subducting lithosphere and Moho offsets beneath westernTibet[J].Earth and Planetary Science Letters,2004,221:117-130.
[21]高锐,黄东定,卢德源,等.横过西昆仑造山带与塔里木盆地结合带的深地震反射剖面[J].科学通报,2000,45(17):1874-1879.
[22]贺日政,赵大鹏,高锐,等.西昆仑造山带下岩石圈地幔速度结构[J].地球物理学报,2006,49(3):778-787.
[23]郑洪伟,李廷栋,高锐,等.印度板块岩石圈地幔向北俯冲到羌塘地体之下的远震P波层析成像证据[J].地球物理学报,2007,50(5):1418-1426.
[24]Wittlinger G,Masson F,Poupinet G,et al.Seismic tomo-graphy of northern Tibet and Kunlun:evidence for crustal blocksand mantle velocity contrasts[J].Earth and Planetary ScienceLetters,1996,139:263-279.
[25]吕庆田,姜枚,许志琴,等.印度板块俯冲仅到特提斯喜马拉雅之下的地震层析证据[J].科学通报,1998,43(12):1308-1311.
[26]Pandey O P.Lithospheric mantle deformation beneath the Indiancratons[J].Journal of Geology,1999,107:683-692.
[27]张进,马宗晋.西藏高原西、中、东的分段性及其意义[J].地质学报,2004,78(2):218-227.
[28]滕吉文,尹周勋,刘宏兵,等.青藏高原岩石层三维和二维结构与大陆动力学[J].地球物理学报,1994,37(增刊II):117-130.
[29]张中杰,李英康,王光杰,等.藏北地壳东西向结构与“下凹”莫霍面———来自宽角反射剖面的启示[J].中国科学:D辑,2001,31(11):881-888.
[30]吴建平,曾融生.青藏高原Q值结构反演[J].地震学报,1996,18(2):208-214.
[31]郑洪伟.青藏高原地壳上地幔三维速度结构及其地球动力学意义[D].北京:中国地质科学院,2006.
[32]Owens T J,Zandt G.Implications of crustal property variationsfor models of Tibetan Plateau evolution[J].Nature,1997,387:37-43.
[33]Molnar P.A review of geophysical constraints on the deep struc-ture of the Tibetan Plateau,the Himalaya and the Karakoram,and their tectonic implications[J].The Philosophical Transac-tions of the Royal Society of London,1988,A326:33-88.
[34]Barazangi M,Ni J.Velocities and propagation characteristics ofPn and Sn beneath the Himalayan Arc and Tibetan Plateau:Pos-sible evidence for underthrusting of Indian continental lithospherebeneath Tibet[J].Geology,1982,10:179-185.
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