接收函数方法获得的和田—拜城剖面壳幔图像
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摘要
利用一个长750 km的宽频地震台阵所采集到的数据和接收函数方法,获得了横穿塔里木盆地的和田—拜城剖面的壳幔图像。和田凹陷、麦盖提斜坡、巴楚隆起、阿瓦提凹陷、塔北隆起、库车凹陷等地块及其边界断裂有清楚显示,各断裂均切穿岩石圈。地壳分为新近系—第四系沉积层、震旦系—古近系沉积层、上地壳结晶基底、中地壳低密度层、下地壳高密度层、下地壳低密度层等6个层。一般而言,各层的密度随深度增加而增加,但有两个层反常。中地壳的密度低于上地壳结晶基底,下地壳下部的密度低于下地壳上部。中地壳低密度层是一不连续的薄层,厚度3～8 km,深度约25 km。下地壳低密度层是一个连续的薄层,厚度5～10 km,深度约45 km。Moho面的深度在盆地北部为40～50 km,巴楚地块为35～55 km,盆地南部为55～60 km。岩石圈底面的深度为70～80 km。塔里木陆块的岩石圈地幔俯冲到西昆仑之下,但地壳并没有俯冲,地壳与地幔发生解耦。吐木休克断裂北侧的北塔里木地块变形微弱,麻札塔格断裂南侧的南塔里木地块变形强烈,两断裂之间的巴楚地块的变形以地壳的弯曲为特征。和田—麦盖提地块是一个整体但变形强烈。在其中识别出5个大的滑脱-推覆断裂面,造成下地壳地层叠覆和缩短,下地壳低密度层以隧道流的方式挤入中地壳。相比之下,沉积盖层几乎没有变形,说明南塔里木的强烈变形发生在震旦纪之前。
Using data collected from an 750-kilometer-long seismic array and receiver function method,we obtain an image of the crust and upper mantle along the Hotan-Baicheng section across the Tarim basin.In the image,Hotan depression,Markit slope,Bachu uplift,Awat depression,Tabei uplift,Kuqa depression and the boundary faults of these blocks are clearly seen.The crust is divided into six layers that are Neogene-Quternary deposition,Sinian-Paleogene deposition,upper crust crystalline basement,mid-crust low density layer,lower crust high density layer,and lower crust low density layer.Generally,the density increase with depth,but two layers are abnormal.The density of the mid-crust is lower than the upper crust crystalline basement,and in the lower crust the density of the lower layer is lower than the upper layer.The mid-crust low density layer is a discontinuous 3～9-km-thick layer,at about 25 km depth.The lower crust low density layer is a continuous 5～10-km-thick layer,at about 45km depth.The depth of Moho is 40～50 km in the northern basin and 50～60km in the southern basin.The depth of the underside of lithosphere is 75～85 km.The lithosphere mantle of the Tarim block underthrust the West Kunlun block,but does not the crust.It indicates the decoupling between the crust and the mantle.In the north of the Tumxuk fault,the North Tarim block is deformed weakly.In the south,the South Tarim block is deformed intensively.The Hotan-Markit-Bachu block is whole and deformed intensively.The five large decollements or thrusts cause imbrication and shortening of the lower crust.But,the sedimental covers deformed very little indicating that the deformation in the South Tarim block had occurred before Sinian or Devonian.Since Neogene,these large decollements or thrusts became active again.
Using data collected from an 750-kilometer-long seismic array and receiver function method,we obtain an image of the crust and upper mantle along the Hotan-Baicheng section across the Tarim basin.In the image,Hotan depression,Markit slope,Bachu uplift,Awat depression,Tabei uplift,Kuqa depression and the boundary faults of these blocks are clearly seen.The crust is divided into six layers that are Neogene-Quternary deposition,Sinian-Paleogene deposition,upper crust crystalline basement,mid-crust low density layer,lower crust high density layer,and lower crust low density layer.Generally,the density increase with depth,but two layers are abnormal.The density of the mid-crust is lower than the upper crust crystalline basement,and in the lower crust the density of the lower layer is lower than the upper layer.The mid-crust low density layer is a discontinuous 3～9-km-thick layer,at about 25 km depth.The lower crust low density layer is a continuous 5～10-km-thick layer,at about 45km depth.The depth of Moho is 40～50 km in the northern basin and 50～60km in the southern basin.The depth of the underside of lithosphere is 75～85 km.The lithosphere mantle of the Tarim block underthrust the West Kunlun block,but does not the crust.It indicates the decoupling between the crust and the mantle.In the north of the Tumxuk fault,the North Tarim block is deformed weakly.In the south,the South Tarim block is deformed intensively.The Hotan-Markit-Bachu block is whole and deformed intensively.The five large decollements or thrusts cause imbrication and shortening of the lower crust.But,the sedimental covers deformed very little indicating that the deformation in the South Tarim block had occurred before Sinian or Devonian.Since Neogene,these large decollements or thrusts became active again.
引文
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[2]肖序常,刘训,高锐,等.西昆仑及邻区岩石圈结构构造演化[J].地质通报,2002,21(2):63-68.Xiao Xuchang,Liu Xun,Gao Rui,et al.Lithospheric structure andtectonic evolution of the West Kunlun and its adjacent areas[J].Geological Bulletin of China,2002,21(2):63-68(in Chinese withEnglish abstract).
[3]刘树根,罗立志,赵锡奎,等.中国西部盆山系统的耦合关系及其动力学模式[J].地质学报,2003,77(2):177-186.Liu Shugen,Luo Lizhi,Zhao Xikui,et al.Coupling relationships ofsedimentary basin-orogenic belt systems and their dynamic modelsin West China[J].Acta Geologica Sinica,2003,77(2):177-186(inChinese with English abstract).
[4]何登发,贾承造,李德生,等.塔里木多旋回叠合盆地的形成与演化[J].石油与天然气地质,2005,26(1):64-77.He Dengyou,Jia Chengzao,Li Desheng,et al.Formation andevolution of polycyclic superimposed Tarim basin[J].Oil&GasGeology,2005,26(1):64-77(in Chinese with English abstract).
[5]许志琴,杨经绥,李海兵,等.造山的高原[M].北京:地质出版社,2007:400-419.Xu Zhiqin,Yang Jingsui,Li Haibing,et al.Orogenic Plateaux[M].Beijing:Geological Publishing House,2007:1-458(in Chinese withEnglish abstract).
[6]肖序常,姜枚.中国西部岩石圈三维结构及演化[M].北京:地质出版社,2008:146-173.Xiao Xuchang,Jiang Mei.The Three-dimensional Structure ofLithosphere and Its Evolution in Western Part of China[M].Beijing:Geological Publishing House,2008:1-225(in Chinese withEnglish abstract).
[7]John Nábělek,Gyrgy Hetényi,Jér觝me Vergne,et al.Underplatingin the Himalaya-Tibet collision zone revealed by the Hi-CLIMBexperiment.Science,2009:1371-1374.
[8]Kosarev G R,Kind S V,Sobolev X,et al.Seismic evidence for adetached indian lithospheric mantle beneath Tibet[J].Science,1999,283:1306-1309.
[9]Kind R X,Yuan J,Saul D,et al.Seismic images of crust and uppermantle beneath Tibet:Evidence for Eurasian Plate Subduction[J].Science,2002,298:1219.
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