中轴构造带(南段)的变形及缩短速率计算
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摘要
中轴构造带是欧亚大陆的一个重要的构造带 ,具有地震震中密集分布、重力梯级、岩石圈厚度或结构变异等特点 ,但没有突兀连贯的山链 ,其原因是多地块的大规模走滑活动的抑制。以往对于中轴构造带的宏观运动和块体之间的相对运动研究得比较深入 ,但是对其缩短变形的研究尚有明显欠缺 ,这使得在讨论青藏高原东向运动是任其“自由逃逸”还是有阻挡性约束的问题时缺乏必要的依据。针对此问题 ,笔者以地块的宏观变形与块体内变形的透入程度为切入点 ,通过编绘横切中轴构造带的平衡剖面 ,计算出该带的缩短率为 2 2 .37% 7.4 3% ,中新世以来的平均缩短速率为 3.6 34.4 5mm/a ,并对中轴构造带形成的变形机制进行了初步探讨。提出青藏高原东向运动受阻 ,中轴构造带内块体东向汇聚下 ,上下地壳拆离并呈现出上叠式仰冲褶皱缩短的认识。
The Central Axis Belt (CAB) is a special tectonic belt within Eurasian continent, along which the epicenters of earthquake are densely distributed; the belt is an important gradient of gravity; the thickness and structure of lithoshpere along the belt change greatly; however, along the belt no continued mountain chains are developed owing to the restrain of the large-scale strike-slip faulting among many blocks. Many researches on the microscopic movement of the CAB and the relative movements among blocks have been carried out before, but the shortenings of deformation have rarely been carried out yet, which leads to the lack of essential basis for the discussion on whether the eastward moving of Qinghai-Tibet Plateau is free or obstructed. Aiming at this problem, the microscopic deformation and degree of penetration of the internal deformation of blocks were taken into account, and with the drawing of the balanced sections across the CAB, the rate of the shortening of this belt was obtained (22.37%~ 27.43%); the average velocity of shortening since the Miocene was also calculated (3.63~4.45mm/a). Based on these, the mechanism of the deformation of the CAB has been discussed preliminarily. Furthermore, we propose that the upper and lower crust of the CAB was detached and the shortening caused by the upstacked overthrusting and folding was presented when the eastward movement of Qinghai-Tibet Plateau was blocked along the CAB.
The Central Axis Belt (CAB) is a special tectonic belt within Eurasian continent, along which the epicenters of earthquake are densely distributed; the belt is an important gradient of gravity; the thickness and structure of lithoshpere along the belt change greatly; however, along the belt no continued mountain chains are developed owing to the restrain of the large-scale strike-slip faulting among many blocks. Many researches on the microscopic movement of the CAB and the relative movements among blocks have been carried out before, but the shortenings of deformation have rarely been carried out yet, which leads to the lack of essential basis for the discussion on whether the eastward moving of Qinghai-Tibet Plateau is free or obstructed. Aiming at this problem, the microscopic deformation and degree of penetration of the internal deformation of blocks were taken into account, and with the drawing of the balanced sections across the CAB, the rate of the shortening of this belt was obtained (22.37%~ 27.43%); the average velocity of shortening since the Miocene was also calculated (3.63~4.45mm/a). Based on these, the mechanism of the deformation of the CAB has been discussed preliminarily. Furthermore, we propose that the upper and lower crust of the CAB was detached and the shortening caused by the upstacked overthrusting and folding was presented when the eastward movement of Qinghai-Tibet Plateau was blocked along the CAB.
引文
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[2] MAZongjin.Thediscussionontheseismicsub regionsofChi nesecontinentandgeodynamics[A ].TheInternationalWork shopontheEvolutionandDynamicsofContinentalLithosh pere—TheProceedingsoftheThirdWorkshoponStructuralGeology(Ⅱ):PreCambrianTectonics,ActiveTectonics,EarthquakeandOthers[C].Beijing:SciencePress,1990.8695(inChinese). [马宗晋.中国大陆地震分区及其动力学讨论[A].国际大陆岩石圈构造演化与动力学讨论会———第三届全国构造地质会议论文选集(Ⅱ):前寒武纪构造、活动构造与地震以及其他[C].北京:科学出版杜,1990.8695.]
[3] MAZongjin,LIXianzhi,JINJiyu.Thelawinterpretationandpredictionofearthquakemigration—EarthquakemigrationoffourseismicbeltsinChina,Mainland[J].SeismologyandGeol ogy,1992,14(2):129138(inChinese). [马宗晋,李献智、金继宇.地震迁移的规律解释和预报———中国大陆四条地震带的地震迁移[J].地震地质,1992,14(2):129138.]
[4] DINGGuoyu.Therecentintraplatemovementandactivetec tonicdeformationinChinesemainland[A].TheInternationalWorkshopontheEvolutionandDynamicsofContinentalLithoshpere—TheProceedingsoftheThirdWorkshoponStruc turalGeology(Ⅱ):PreCambrianTectonics,ActiveTecton ics,EarthquakeandOthers[C].Beijing:SciencePress,1990.7385(inChinese). [丁国瑜.我国大陆的新构造变形与板内现代运动[A].国际大陆岩石圈构造演化与动力学讨论会———第三届全国构造地质会议论文选集(Ⅱ):前寒武纪构造、活动构造与地震以及其他[C].北京:科学出版社,1990.7385.]
[5] DINGGuoyu.TheConspectusoftheLithosphericDynamicsofChina[M].Beijing:SeismologicalPress,1991(inChinese). [丁国瑜.中国岩石圈动力学概论[M ].北京:地震出版社,1991.]
[6] ZHANGZonghu.TheIlluminatingBookandGeologicalMapoftheP .R .CandVicinalOceans[Z].Beijing:SinoMapsPress,1990(inChinese). [张宗祜.中华人民共和国及其毗邻海区第四纪地质图及其说明书[Z].北京:中国地图出版杜,1990.]
[7] SONGFangmin,WANGYipeng,DENGQidong,etal.TheXiaojiangActiveFaultBelt[M ].Beijing:SeismologicalPress,1998.1237(inChinese). [宋方敏,汪一鹏,邓启东,等.小江活动断裂带[M ].北京:地震出版社,1998.237.]
[8] YINXiuhua,SHIZhihong,LIUZhanpo,etal.Thebasicfea turesofregionalgravityfieldinChinesecontinent[J].Seismolo gyandGeology,1980,2(4):6975(inChinese). [殷秀华,史志宏,刘占坡,等.中国大陆区域重力场基本特征[J].地震地质,1980,2(4):6975.]
[9] CHENXuebo.ThevelocitycharacteristicsofcrustalongtwosidesofLongmenshantectonicbelt[A].TheProgressandStudyontheDeepStructuresofChineseContinent[M ].Beijing:Seis mologicalPress,1991.97113(inChinese). [陈学波.龙门山构造带两侧地壳速度结构特征[A].中国大陆深部构造的研究与进展[M ].北京:地震出版社,1991.97113.]
[10] TENGJiwen,ZENGRongsheng.ThedistributionindepthoftheMohosurfaceandbasictectonicframearoundtheEastAsiancontinentandvicinaloceans[J].ScienceinChina(SeriesD),2002,32(2):89100(inChinese). [膝吉文,曾融生.东亚大陆及周边海域Moho界面深度分布和基本构造格局[J].中国科学(D),2002,32(2):89100.]
[11] LIWeijuan,LIANGGuipei,YAOZhengsheng.TherelationshipbetweenearthquakesandgeophysicalfieldsoftheLongmenshanandadjacentareas[J].EarthquakeofSoutheastChina,1995,15(2):7185(inChinese). [李渭娟,梁桂培,姚政生.龙门山及邻区地球物理场与地震的关系[J].华南地震,1995,15(2):7185.\〗
[12] WANGQi,ZHANGPeizhen,MAZongjin.GPSdatabaseandvelocityfieldofcontemporarytectonicdeformationincontinentalChina[J].EarthScienceFrontiers,2002,9(2):430441(inChinese). [王琪,张培震,马宗晋.中国大陆现今构造变形GPS观测数据与速度场[J].地学前缘,2002,9(2):430441.]
[13] ZHANGPeizhen,WANGQi,MAZongjin.GPSsvelocityfieldandactivecrustalblocksofcontemporarytectonicdeformationincontinentalChina[J].EarthScienceFrontiers,2002,9(2):430438(inChinese). [张培震,王琪,马宗晋.中国大陆现今构造运动的GPS速度场与活动地块[J].地学前缘,2002,9(2):430438.]
[14] FUYang,ZHUWenyao,WANGXiaoya,etal.Theinvestiga tionsoncrustaldeformationinChinaunderITRF97platemodelusingdataofcrustalmovementobservationnetworkinChina[J].2002,45(3):33033(inChinese). [符养,朱文耀,王小亚,等.利用中国地壳运动观测网络研究中国大陆相对于ITRF97板块模型形变[
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