青藏高原东北缘深地震测深震相研究与地壳细结构
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摘要
通过对青藏高原东北缘不同构造单元深地震测深资料震相的综合分析,利用反射率理论地震图方法对实际记录模拟计算,进一步研究东北缘区域内部不同构造单元地壳细结构.结果显示:西秦岭褶皱造山带分隔了南北不同性质的地壳结构,北侧为相对稳定的临夏—兰州新生代盆地、南侧为强烈改造的松潘—甘孜地块;松潘—甘孜地块在青藏高原东北缘的构造演化过程中改造为萎缩的若尔盖高原盆地和盆地边缘褶皱造山两类不同的地壳结构;青藏高原东北缘中下地壳普遍存在以多层高低速相间、低速度结构为主的破碎松弛结构,这种特征在缝合带和造山带尤为明显,显示为地壳形变增厚、流变滑动的重要场所;结合二维速度结构及GPS研究结果,对青藏高原东北缘地壳形变及动力学过程进行了讨论.
In this paper the fine crust structures of the different tectonic units in the northeastern margin of Tibetan plateau are investigated in detail by means of comprehensive analyses of the crust phases on the recording sections of deep seismic sounding experiments in this region and comparing the observed seismic recording sections with the synthetic seismograms computed by the reflectivity method.The results reveal that the crust structures in the northern and southern parts of this region separated by the western Qinlin fold zone are quite different,and the crust structures are characterized respectively by stable Linxia-Lanzhou Cenozoic basin in the northern part and by strongly rebuilt Songpan-Garze tectonic block in the southern part.The results also show that Songpan-Ganzi tectonic block was rebuilt into two types of crust structures,i.e.the type of the shrunken Zoigê upland basin and the type of the folded orogenic zone in the basin margin.It is also revealed that fractured and relaxed structures widely exist in the middle and lower crust in the northeastern margin of Tibetan plateau,which are characterized by alternative low and high velocity structures or low velocity distributions.This structural feature appears especially obvious in the suture zone and the orogenic zone,which implies there are important places of thickening of the crust and rheological slip motion.The crust deformation and geodynamic process are discussed based on the 2D velocity structure of the crust and GPS result obtained in this region.
In this paper the fine crust structures of the different tectonic units in the northeastern margin of Tibetan plateau are investigated in detail by means of comprehensive analyses of the crust phases on the recording sections of deep seismic sounding experiments in this region and comparing the observed seismic recording sections with the synthetic seismograms computed by the reflectivity method.The results reveal that the crust structures in the northern and southern parts of this region separated by the western Qinlin fold zone are quite different,and the crust structures are characterized respectively by stable Linxia-Lanzhou Cenozoic basin in the northern part and by strongly rebuilt Songpan-Garze tectonic block in the southern part.The results also show that Songpan-Ganzi tectonic block was rebuilt into two types of crust structures,i.e.the type of the shrunken Zoigê upland basin and the type of the folded orogenic zone in the basin margin.It is also revealed that fractured and relaxed structures widely exist in the middle and lower crust in the northeastern margin of Tibetan plateau,which are characterized by alternative low and high velocity structures or low velocity distributions.This structural feature appears especially obvious in the suture zone and the orogenic zone,which implies there are important places of thickening of the crust and rheological slip motion.The crust deformation and geodynamic process are discussed based on the 2D velocity structure of the crust and GPS result obtained in this region.
引文
1)地质矿产部.中国布格重力异常图.1992
[1]张国伟,郭安林,姚安平.中国大陆构造中的西秦岭—松潘大陆构造结.地学前缘,2004,11(3):23～32Zhang G W,Guo A L,Yao A P.Western Qinling-Songpan continental tectonic node in China′s continental tectonics.Earth Science Frontiers(in Chinese),2004,11(3):23～32
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[1]张国伟,郭安林,姚安平.中国大陆构造中的西秦岭—松潘大陆构造结.地学前缘,2004,11(3):23～32Zhang G W,Guo A L,Yao A P.Western Qinling-Songpan continental tectonic node in China′s continental tectonics.Earth Science Frontiers(in Chinese),2004,11(3):23～32
[2]马杏垣主编.中国岩石圈动力学地图集.北京:中国地图出版社,1989,49,54,55Edit by Ma X Y.Lithospheric Dynamics Atlas of China(in Chinese).Beijing:China Cartographic Publishing House,1989,49,54,55
[3]杨经绥,许志琴,李海兵等.东昆仑阿尼玛卿地区古特提斯火山作用和板块构造体系.岩石矿物学杂志,2005,24(5):369～380Yang J S,Xu Z Q,Li H B.et al.The plate-Tethyan volcanismand plate tectonic regimein the A′nyemaqen region of East Kunlun,northern Tibet Plateau.Acta Petrologicaet Mineralogica(in Chinese),2005,24(5):369～380
[4]边千韬,罗小全,陈海泓等.阿尼玛卿蛇绿岩带花岗—英云闪长岩锆石U-Pb同位素定年及大地构造意义.地质科学,1999,34(4):420～426Bian Q T,Luo X Q,Chen H H,et al.Zircon U-Pb age of granodiorite-tonalite in the A′nyemaqen ophiolitic belt andits tectonic significance.Scientia Geologica Sinica(in Chinese),1999,34(4):420～426
[5]许志琴,侯立玮,王宗秀.松潘—甘孜造山带构造研究新进展.中国地质,1991,(2):16～18Xu Z Q,Hou L W,Wang Z X.Newdevelopment of studyingthe Songpan-Ganzi orogen structure.Geology in China(in Chinese),1991,(2):16～18
[6]王椿镛,韩渭宾,吴建平等.松潘—甘孜造山带地壳速度结构.地震学报,2003,25(3):229～241Wang C Y,Han W B,Wu J P,et al.Crustal structure beneath the Songpen-Ganzi orogenic belt.Acta Seismologica Sinica(in Chinese),2003,25(3):229～241
[7]李松林,张先康,张成科等.玛沁—兰州—靖边地震测深剖面地壳速度结构初步研究.地球物理学报,2002,45(2):210～217Li S L,Zhang X K,Zhang C K,et al.Apreliminary study on the crustal velocity structure of Maqin-Lanzhou-Jingbian by means of deep seismic sounding profile.Chinese J.Geophys.(in Chinese),2002,45(2):210～217
[8]崔作舟,陈纪平,吴苓.阿尔泰—台湾岩石圈地学断面综合研究:花石峡—邵阳深部地壳的结构和构造.北京:地质出版社,1996.49～168Cui Z Z,Chen J P,Wu L.A Comprehensive Study of the Alatai-Tai wan Lithospheric Geotransect:Deep Crustal Structure and Tectonics from Huashixia to Shaoyang(in Chinese).Beijing:Geological Publishing House.1996.49～168
[9]王椿镛,林中洋,陈学波.青海门源—福建宁德地学断面综合地球物理研究.地球物理学报,1995,38(5):590～598Wang C Y,Lin Z Y,Chen X B.Comprehensive study of geophysics on geoscience transect from Menyuan,Qinghai province,to Ningde,Fujian province,China.Chinese J.Geophys.(in Chinese),1995,38(5):590～598
[10]闵祥仪,周民都,郭建康等.灵台—阿木去乎剖面地壳速度结构.西北地震学报,1991,13(增刊):37～43Min X Y,Zhou M D,Guo J K,et al.The crustal velocity structure in Lingtai-Amuqugu profile.Northwestern Seismological Journal(in Chinese),1991,13(Suppl.):29～36
[11]陈学波,吴跃强,杜平山等.龙门山构造带两侧地壳速度结构特征.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,1988,97～113Chen X B,Wu Y Q,Du P S,et al.Crustal velocity structure at the two sides of Longmenshan tectonic belt.In:Depart ment of Scientific Programming and Earthquake Monitoring eds.Developments in the Research of Deep Structures of China′s Continent(in Chinese).Beijing:Geological Publishing House,1988,97～113
[12]曾融生,孙为国,毛桐恩等.中国大陆莫霍界面深度图.地震学报,1995,17(3):322～327Zeng R S,Sun WG,Mao T E,et al.The depth of Mohoin the mainland of China.Acta Seismologica Sinica(in Chinese),1995,17(3):322～327
[13]冯锐.中国地壳厚度及上地幔密度分布(三维重力反演结果).地震学报,1985,7(2):143～156Feng R.Crustal thickness and densities in the upper mantle beneath China-the results of three dimension gravity inversion.Acta Seismologica Sinica(in Chinese),1985,7(2):143～156
[14]高锐,马永生,李秋生等.松潘地块与西秦岭造山带下地壳的性质和关系—深地震反射剖面的揭露.地质通报,2006,25(12):1361～1367Gao R,Ma T S,Li Q S,et al.Structure of the lower crust beneath the Songpan block and West Qinling orogen andtheir relation as revealed by deep seismic reflection profiling.Geological Bulletin of China(in Chinese),2006,25(12):1361～1367
[15]嘉世旭,刘昌铨.华北地区人工地震测深震相与地壳结构研究.地震地质,1995,17(2):97～105Jia S X,Liu C Q.Study onthe seismic phase of DSSin North China.Seismology and Geology(in Chinese),1995,17(2):97～105
[16]张先康,嘉世旭,赵金仁等.西秦岭—东昆仑及邻近地区地壳结构—深地震宽角反射/折射剖面结果.地球物理学报,2008,51(2):439～450Zhang X K,Jia S X,Zhao J R,et al.Crust structures beneath West Qinling-East Kunlun orogen and its adjacent area-Result of wide-angle seismic reflection and refraction experiment.Chinese J.Geophys.(in Chinese),2008,51(2):439～450
[17]马丽芳主编.中国地质图集.北京:地质出版社,2002,10,92～96Edit by Ma L F.Geology Atlas of China(in Chinese).Beijing:Geological Publishing House,2002,10,92～96
[18]Zhao W J,Nelson K D,Project I NDEPTH Team.Deep seismic reflection evidence for continental underthrusting beneath south Tibet.Nature,1993,366(9):557～559
[19]Ross A,Brown L,Passakorn P,et al.Deep reflection surveying in central Tibet:lower-crustal layering and crustal flow.Geophysical Journal International,2004,156:115～128
[20]卢占武,高锐,李秋生等.中国青藏高原深部地球物理探测与地壳动力学研究(1958～2004).地球物理学报,2006,49(3):753～770Lu Z W,Gao R,Li Q S,et al.Deep geophysical probe and geodynamic study onthe Qinghai-Tibet Plateau(1958-2004).Chinese J.Geophys.(in Chinese),2006,49(3):753～770
[21]Fuchs Muller G.Computation of synthetic seismograms with the reflectivity method and comparison with observation.Geophysics,1971,23:417～423
[22]张先康,李松林,王夫运等.青藏高原东北缘、鄂尔多斯和唐山的地壳结构差异—深地震测深的结果.地震地质,2003,25(1):52～62Zhang X K,Li S L,Wang F Y,et al.Differences of crustal structures in northeastern edge of Tibet plateau,Ordos and Tangshan earthquake region in north China-results of deep seismic sounding.Seismology and Geology(in Chinese),2003,25(1):52～60
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