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
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摘要
通过分析阿尔金—龙门山地学断面的地震资料 ,建立了该剖面的地壳纵波速度结构 .研究结果表明 ,阿尔金北侧的塔里木盆地地区莫霍面为 5 0km ,而在其南侧的祁连地块莫霍面突然加深至 73km ,在柴达木盆地莫霍面又抬升至 5 8km左右 ,然后 ,在松潘甘孜地块莫霍面降至 70km ,并呈现为台阶状向龙门山方向抬升到 6 0km左右 ,最后在四川盆地 ,莫霍面的埋深仅为 5 2km .以昆仑断裂为界 ,在其北部地区的中地壳底部存在一速度为 5 80km s的低速层 ,而在其南部地区则没有低速层出现 ,推测低速层为地壳中部的局部熔融物质 .阿尔金—龙门山剖面上的两个莫霍面坳陷区分别与祁连地块和松潘—甘孜地块上的两个莫霍面坳陷区相对应 ,指示出这两个地块具有较深的山根 ,青藏高原北部的巨厚地壳很可能是由于中生代以来发生的印度板块与亚洲板块碰撞时受到来自东西及南北方向的挤压 ,使地壳缩短所致 .
Based upon the seismic experiments along Geoscience Transect from the Altyn Tagh to the Longmen Mountains,the crustal P-wave velocity structure was derived to outline the characteristics of the crustal structure.The section shows a few significant features.The crustal thickness varies dramatically,and is consistent with tectonic settings.The Moho boundary abruptly drops to 73km depth beneath the southern Altyn Tagh from 50km below the Tarim basin,then rises again to about 58km depth beneath the Qaidam basin.Finally,the Moho drops again to about 70km underneath the Songpan-Garze Terrane and rises to 60km near the Longmen Mountains with a step-shape.Further southeast,the crust thins to 52km beneath the Sichuan basin in the southeast of the Longmen Mountains.In the north of the Kunlun fault,a low-velocity zone,which may be a layer of melted rocks due to high temperature and pressure at depth,exists in the the bottom of the middle crust.The two depressions of the Moho correlate with the Qilian and Songpan-Garze terranes,implying that these two mountains have thick roots.According to our results,it is deduced that the thick crust of the northeastern Tibetan Plateau probably is a result of east-west and northwest-southeast crustal shortening since Mesozoic time during the collision between the Asian and Indian plates.
Based upon the seismic experiments along Geoscience Transect from the Altyn Tagh to the Longmen Mountains,the crustal P-wave velocity structure was derived to outline the characteristics of the crustal structure.The section shows a few significant features.The crustal thickness varies dramatically,and is consistent with tectonic settings.The Moho boundary abruptly drops to 73km depth beneath the southern Altyn Tagh from 50km below the Tarim basin,then rises again to about 58km depth beneath the Qaidam basin.Finally,the Moho drops again to about 70km underneath the Songpan-Garze Terrane and rises to 60km near the Longmen Mountains with a step-shape.Further southeast,the crust thins to 52km beneath the Sichuan basin in the southeast of the Longmen Mountains.In the north of the Kunlun fault,a low-velocity zone,which may be a layer of melted rocks due to high temperature and pressure at depth,exists in the the bottom of the middle crust.The two depressions of the Moho correlate with the Qilian and Songpan-Garze terranes,implying that these two mountains have thick roots.According to our results,it is deduced that the thick crust of the northeastern Tibetan Plateau probably is a result of east-west and northwest-southeast crustal shortening since Mesozoic time during the collision between the Asian and Indian plates.
引文
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[2]肖序常,李廷栋,王 军.青藏高原大陆动力学.见:肖序常,李廷栋主编.青藏高原的构造演化与隆升机制.广州:广东科技出版社,2000237～270Xiao,XX ,LiTD ,WangJ .ContinentaldynamicsoftheQinghaiXizang(Tibet)plateau.In:XiaoXC ,LiTDed.TectonicEvolutionandUpliftofQinghaiXizang(Tibet)Plateau(inChinese).Guangzhou:GuangdongScience&TechnologyPress,2000.237～270
[3]滕吉文,熊绍柏.喜马拉雅山北部地区的地壳结构模型和速度分布特征.地球物理学报,1983,26(6):525～540TengJW ,XiongSB .ThecrustalstructuremodelandthecharacteristicsofthevelocitydistributioninthenorthoftheHimalayaMountain.ChineseJ .Geophys.(inChinese),1983,26(6):525～540
[4]崔作舟,李秋生,吴朝东等.格尔木—额济纳旗地学断面的地壳结构与深部构造.地球物理学报,1995,38(增刊):15～28CuiZZ ,LiQS ,WuCD ,etal.ThecrustalanddeepstructuresinGolmodEjinQiGGT .ChineseJ .Geophys.(inChinese),1995,38(Suppl.):15～28
[5]王有学,钱 辉.青海东部地壳速度结构特征研究.地学前缘,2000,7(4):568～579WangYX ,QianH .StudyofcrustalvelocitystructureinEastQinghai.EarthScienceFrontiers(inChinese),2000,7(4):568～579
[6]MolnarP .AreviewofgeophysicalconstraintsonthedeepstructureoftheTibetanPlateau,theHimalayaandKarakoram,andtheirtectonicinterpretion.Philos.Trans.R .Soc.London(Ser.A),1988,326:33～88
[7]ZhuL ,HelmbergerDV .MohooffsetacrossthenorthernmarginofTibetanplateau.Science,1998,281:1170～1172
[8]HarrisonTM ,CopelandP ,KiddWSF ,etal.RaisingTibet.Science,1992,255:1663～1670
[9]王有学,韩国华.青藏高原东缘二维地壳速度结构及其区域地质构造.见:袁学诚主编.阿尔泰—台湾地学断面论文集.武汉:中国地质大学出版社,199756～70WangYX ,HuanGH .2DcrustalvelocitystructureandtheregionaltectonicsintheeastmarginofTibetanPlateau.In:YuanXCed.MemoirsoftheGeoscienceTransectionfortheContinentalLithospherebeneathAltay—Taiwan,China(inChinese).Wuhan:ChinaUniversityofGeosciencesPress,199756～70
[10]WangYX .2DCrustalVelocityStructureandRegionalTectonicsinEastMarginofTibetPlateau.In:Abstractsof30 thIGC ,Japan,Vol.3,1996107
[11]李春昱.中国板块构造轮廓.中国地质科学院院报,1980,2(1):1～12LiCY .AntectonicoutlineofChina.ActaGeoscientiaSinica(inChinese),1980,2(1):1～12
[12]崔军文.阿尔金断裂系.北京:地质出版社,199994～102CuiJW .AltunFaultSystem.Beijing:GeologicalPublishingHouse,199994～102
[13]谢明谦.柴达木盆地基底花岗岩的形成及其陆壳的消融作用.见:徐贵中,常承法主编.大陆岩石圈构造与资源.北京:海洋出版社,199294～106XieMQ .TheformationofthegraniterocksinthebasementoftheQaidambasinanditscrustalmelting.In:XuGZ ,ChangCFed.ContinentalLithosphereStructureandResources.Beijing:OceanPress,199294～106
[14]许志琴,侯立玮,王宗秀.中国松潘甘孜造山带的造山过程.北京:地质出版社,1992XuZQ ,HouLW ,WangZX .OrogenicProcessinSongpanGarzeOrogenicBelt.Beijing:GeologicalPublishingHouse,1992
[15]HoleJA .Nonlinearhigh resolutionthree dimensionalseismictraveltimetomography.J .Geophys.Res.,1992,97:6553～6562
[16]GieseP ,ProdehlC ,SteinA .ExplosionSeismologyinCentralEurope.BerlinHeidelberg,NewYork:SpringerVerlag,1976146～161
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[18]FuchsK ,M櫣llerG.Computationofsyntheticseismogramswiththereflectivitymethodandcomparisonwithobservations.Geophys.J .R .Astr.Soc.,1971,23:417～433
[19]王有学,韩果花,姜 枚等.阿尔泰—阿尔金地学断面地壳结 构.地球物理学报,2004,47(2):240～249WangYX ,HanGH ,JiangM ,etal.ThecrustalstructurealonggeosciencetransectfromAltaytoAltynTagh.ChineseJ .Geophys.(inChinese),2004,47(2):240～249
[20]孔祥儒.高原地壳加厚的方式与机制.见:潘裕生,孔祥儒主编.青藏高原岩石圈结构演化和动力学.广州:广东科技出版社,1998365～378KongXR .CrustalthickeningpatternandmechanismofQinghaiXizang(Tibetan)plateau.In:PanYS ,KongXReds.LithosphereStructure,EvolutionandDynamicsofQinghaiXizang(Tibetan)Plateau(inChinese).Guangzhou:GuangdongScience&TechnologyPress,1998365～378
[21]张家骏.苏联科拉半岛超深钻.安徽地质科技,1987,(1):53～57ZhangJJ.SuperdeepdrillinginKolapeninsula,SovietUnion.AnhuiGeologicalTechnology(inChinese),1987,(1):53～57
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