青藏高原东缘龙门山逆冲构造深部电性结构特征
摘要
通过对汶川地震前观测的碌曲—若尔盖—北川—中江大地电磁剖面的数据处理和反演解释,揭示了沿剖面的松潘—甘孜地块、川西前陆盆地、龙门山构造带及秦岭构造带50 km深度的电性结构特征及相互关系,表明青藏高原东缘向东挤压,迫使向东流动的地壳物质沿高原东缘堆积,并向扬子陆块逆冲推覆.龙门山恰好位于松潘—甘孜地块与扬子陆块对挤部位,主要受松潘—甘孜地块壳内高导层滑脱和四川盆地基底高阻体阻挡的约束,地壳深部存在着西倾且连续展布的壳内低阻层,表明龙门山深部确实存在着逆冲推覆构造,其逆冲断裂系中的三条断裂不仅以不同的倾角向西北倾斜,并且向深部逐渐汇集,但茂县—汶川断裂可能在深部与北川—映秀断裂是分离的.龙门山两翼的四川盆地和松潘甘孜褶皱带的电性结构既具有明显差异性,又具有一定的相关性.四川盆地显示巨厚的低阻沉积盖层和连续稳定的高阻基底的二元电性结构,而松潘—甘孜地块则表现为反向二元结构,即上部大套高阻褶皱带,下部整体为低阻的变化带,龙门山逆冲构造带本身又表现为松潘地块逆冲上覆在四川盆地之上,构成上部高阻褶皱带、中部低阻逆冲断裂带和底部盆地高阻基底的三层电性结构.对比龙门山逆冲构造断裂带的西倾延伸上下盘两侧的两个反对称的二元电性结构,松潘区块深部推断的结晶基底与龙门山断裂带下盘推断的下伏盆地结晶基底又存在某种内在对应关系,推断可能存在一个西延至若尔盖地块的泛扬子陆块.因此,龙门山构造带地壳电性结构研究对于揭示青藏高原东缘陆内造山动力过程,探索汶川大地震的深部生成机理都具有重要意义.
By processing, interpreting and inverting the magnetotelluric observation data obtained before the Wenchuan earthquake along the Luqu-Zhongjiang profile passing through Qinling Tectonic Zone, Songpan-Garze block and Longmen Shan Mountains, as well as Sichaun Basin, this paper reveals the crust architecture above 50 km depth of the Eastern Qinghai-Tibet Plateau and Western Sichuan foreland basin and the relationship between them. The eastward pressing of Qinghai-Tibet Plateau forces the Songpan-Garze block thrusting upon the Yangzi block, which obstructs the eastward movement of Qinghai-Tibet Plateau. The Longmen Shan is located at the joint of two blocks and it is found that there is a west-inclined low-conductivity layer in the crust at 10-20 km depth beneath the Longmen Shan Mountain, it is deduced as the deep conductivity characteristics of thrust belt structure in Longmen Shan tectonic zone. The three main faults of Maoxian-Wenchaun, Beichuan-Yingxiu and Peng-Guan of Longmen Shan fault belt dip to NW with different dip angles. The two faults of Beichuan-Yingxiu and Peng-Guan seem to converge together in the deep but they are probably separated with the Maoxian-Wenchaun fault. There are different characters between the Sichuan basin and Songpan-Garze fold belt located at the two sides of Longmen Shan. The Sichuan basin has a thick low-resistance sedimentary layer on a stable high-resistance basement, while Songpan-Garze block has high resisitivity cover of upper crust with continuous low resistance bed of the crust. Resulted from Songpan-Garze block thrusting onto the Sichuan Basin stable block, Longmen Shan tectonic zone formed a three-layer geoelectrical structure with high resistance in the upper and lower part and low resistance thrust fault zone in the middle. So the research on the MT profile is important for both continent dynamics in the orogenic zone and deep mechanism of Wenchuan earthquake at Longmeshan fault zone in the east of Qinghai-Tibet plateau.
By processing, interpreting and inverting the magnetotelluric observation data obtained before the Wenchuan earthquake along the Luqu-Zhongjiang profile passing through Qinling Tectonic Zone, Songpan-Garze block and Longmen Shan Mountains, as well as Sichaun Basin, this paper reveals the crust architecture above 50 km depth of the Eastern Qinghai-Tibet Plateau and Western Sichuan foreland basin and the relationship between them. The eastward pressing of Qinghai-Tibet Plateau forces the Songpan-Garze block thrusting upon the Yangzi block, which obstructs the eastward movement of Qinghai-Tibet Plateau. The Longmen Shan is located at the joint of two blocks and it is found that there is a west-inclined low-conductivity layer in the crust at 10-20 km depth beneath the Longmen Shan Mountain, it is deduced as the deep conductivity characteristics of thrust belt structure in Longmen Shan tectonic zone. The three main faults of Maoxian-Wenchaun, Beichuan-Yingxiu and Peng-Guan of Longmen Shan fault belt dip to NW with different dip angles. The two faults of Beichuan-Yingxiu and Peng-Guan seem to converge together in the deep but they are probably separated with the Maoxian-Wenchaun fault. There are different characters between the Sichuan basin and Songpan-Garze fold belt located at the two sides of Longmen Shan. The Sichuan basin has a thick low-resistance sedimentary layer on a stable high-resistance basement, while Songpan-Garze block has high resisitivity cover of upper crust with continuous low resistance bed of the crust. Resulted from Songpan-Garze block thrusting onto the Sichuan Basin stable block, Longmen Shan tectonic zone formed a three-layer geoelectrical structure with high resistance in the upper and lower part and low resistance thrust fault zone in the middle. So the research on the MT profile is important for both continent dynamics in the orogenic zone and deep mechanism of Wenchuan earthquake at Longmeshan fault zone in the east of Qinghai-Tibet plateau.
引文
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[4] 许志琴,侯立玮,王宗秀等.中国松潘-甘孜造山带的造山过程.北京:地质出版社,1992 Xu Z Q, Hou L W, Wang Z X, et al . Orogenic Process of the Songpan-Ganzi Orogen in China (in Chinese). Beijing: Geological Publishing House, 1992
[5] 滕吉文.中国地壳与上地幔的地球物理探测.地球物理学报,1997,22(4) :346-350． Teng J W. Geophysical investigation of the Earth s crust and upper mantie in China. Chinese J. Geophys. ( Acta Geophysica Sinica) (in Chinese), 2005, 48(3) :411-418
[6] 李立,金国元.攀西裂谷带及龙门山断裂带地壳上地幔的大地电磁测深研究.物探与化探,1987,11(3) :161-169 Li L, Jin G Y. Telluric electromagnetic sounding study of crust and upper mantle in the Panxi " Rift Zone" and the Longmen Shan faulted zone. Geophysical and Geochemical Exploration (in Chinese) , 1987, 11(3) :161-169
[7] 王运生,王绪本,苟量等.松潘-邵阳大地电磁剖面深、浅部典型构造的解释.南水北调与水利科技,2007,5(2) :70-77 Wang Y S, Wang X B, Gou L, et al. Several Progress of Deep-shallow Structure Interpretation by MT along Songpan-Shaoyang Cross Section. South-to-North Water Transfers and Water Science & Technology (in Chinese), 2007, 5(2) :70-77
[8] 王绪本,李永年,高永才.大地电磁测深二维地形影响及其校正方法研究.物探化探计算技术,1999,21(4) :328-332 Wang X B, Li Y N, Gao Y C. Two dimensional topographic responses in magneto telluric sounding and its correction methods. Computing Techniques for Geophysical and Geochemical Exploration (in Chinese) , 1999, 21(4) :328-332
[9] 赵国泽,汤吉,詹艳等.青藏高原东北缘地壳电性结构和地块变形关系的研究.中国科学(D辑),2004,34(10) :908-918 Zhao G Z, Tang J, Zhan Y, et al. Relation between electricity structure of the crust and deformation of crustal blocks on the northeastern margin of Qinghai-Tibet Plateau. Science in China (Ser. D) (in Chinese),2004,34(10) :908-918
[10] 赵国泽,陈小斌,王立凤等.青藏高原东边缘地壳“管流”层的电磁探测证据.科学通报,2008,53(3) :345-350 Zhao G Z, Chen X B, Wang L F, et al. Magnetotelluric evidence of the crustal 'channel flow' , the eastern Qinghai-Tibet Plateau. Chinese Science Bulletin (in Chinese), 2008, 53(3) :345-350
[11] 孙洁,晋光文,白登海等.青藏高原东缘地壳上地幔电性结构探测及其构造意义.中国科学(D辑),2003,33(增刊):173-180 Sun J, Jin G W, Bai D H, et al. Sounding of electrical structure of the crust and upper mantle along the eastern border of Qinghai-Xizang plateau and its tectonic significance. Science in China (D) (in Chinese), 2003,33(Suppl.):173-180
[12] 汤吉,詹艳,赵国泽等.青藏高原东北缘玛沁-兰州-靖边剖面地壳上地幔电性结构研究.地球物理学报,2005,48(5) :1205-1216 Tang J, Zhan Y, Zhao G Z, et al. Electrical conductivity structure of the crust and upper mantle along the profile Maqin-Lanzhou-Jingbian in the northeastern margin of the Qinghai-Tibet plateau. ChineseJ.Geophys.,(in Chinese), 2005,48(5) :1293-1306
[13] 马晓冰,孔祥儒,刘宏兵等.青藏高原东北部地区地壳电性结构特征.地球物理学报,2005,48(3) :689-697 Ma X B, Kong X R, Liu H B, et al. The electrical structure of northeastern Qinghai-Tibet plateau. Chinese J. Geophys. (in Chinese), 2005,48(3) :689-697
[14] 詹艳,赵国泽,王继军等.青藏高原东北缘海原弧形构造区地壳电性结构探测研究.地震学报,2005,27(4) :431-440 Zhan Y, Zhao G Z, Wang J J, Tang J, et al. Crustal electric structure of Haiyuan actuate tectonic region in the northeastern margin of Qinghai-Xizang plateau, China. Acta Seismologica Sinica (in Chinese), 2005, 27(4) :431-440
[15] 王绪本,余年,朱迎堂.龙门山逆冲构造带大地电磁测深初步成果.成都理工大学学报,2008,35(4) :398-403 Wang X B, Yu N, Zhu Y T , et al. Preliminary result of magnetotelluric sounding in the Longmenshan thrust belt of West Sichuan, China. Journal of Chengdu University of Technology (in Chinese) , 2008, 21(4) :398-403
[16] 王椿镛,吴建平,楼海.青藏高原东部壳幔速度结构和地幔变形场的研究.地学前缘,2006,13(5) :349-359 Wang C Y, Wu J P, Lou H. Study of crustal and upper mantle s structure and mantle deformation field beneath the eastern Tibetan plateau. Earth Science Frontiers ( in Chinese), 2006,13(5) :349-359
[17] Constable C S, Parker R L, Constable C G. Occam' s inversion: A practical algorithm for generating smooth models from electromagnetic sounding data. Geophysics, 1987,52:289-300
[18] William R, Randall L M. Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion. Geophysics, 2001,66(1) :174-187
[19] Burchfiel B C, Chen Z, Liu Y, et al. Tectonics of the Longmenshan and adjacent regions, Central China. International Geology Review, 1996, 37:661-735
[20] 崔作舟,陈纪平,吴苓.花石峡-邵阳深部地壳的结构和构造.北京:地质出版社,1996 Cui Z Z, Chen J P, Wu L. Texture and Structure of Huashixia-Shaoyang Deep Crust (in Chinese). Beijing: Geological Publishing House, 1996
[21] 郭正吾,邓康龄,韩永辉等.四川盆地形成与演化.北京:地质出版社,1996 Guo Z W, Deng K L, Han Y H, et al. Formation and Development of Sichuan Basin (in Chinese). Beijing:Geological Publishing House , 1996
[22] 殷鸿福,吴顺宝,杜远生等.华南是特提斯多岛洋体系的一部分.地球科学 中国地质大学,1999,24(1) :1-12 Yin H F, Wu S B, Du Y S, et al. South China defined as part of Tethyan archipelagic ocean system. Earth Science Journal of China University of Geosciences (in Chinese), 1999,24(1) :1-12
[23] 高锐,王海燕,马永生等.松潘地块若尔盖盆地与西秦岭造山带岩石圈尺度的构造关系-深地震反射剖面探测成果.地球学报,2006,27(5) :411-418 Gao R,Wang H Y, Ma Y S, et al. Tectonic relationships between the Zoige basin of the Songpan block and the west Qinling orogen at lithosphere scale: results of deep seismic reflection profiling. Acta Geoscientica Sinica (in Chinese), 2006, 27(5) : 411-418
[2] 任纪舜,姜春发,张正坤等.中国大地构造及其演化.北京:科学出版社,1980 Ren J S, Jiang C F, Zhang Z K, et al. China Continental Structure and Its Evolution (in Chinese) . Beijing: Science Press, 1980
[3] 张国伟,郭安林,姚平安.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) :23-32 Zhang G W, Guo A L , Yao P A. Western Qinling-Songpan continental tectonic node in Chinese continental tectonic. Earth Science Frontiers (in Chinese), 2004, 11(3) :23-32
[4] 许志琴,侯立玮,王宗秀等.中国松潘-甘孜造山带的造山过程.北京:地质出版社,1992 Xu Z Q, Hou L W, Wang Z X, et al . Orogenic Process of the Songpan-Ganzi Orogen in China (in Chinese). Beijing: Geological Publishing House, 1992
[5] 滕吉文.中国地壳与上地幔的地球物理探测.地球物理学报,1997,22(4) :346-350． Teng J W. Geophysical investigation of the Earth s crust and upper mantie in China. Chinese J. Geophys. ( Acta Geophysica Sinica) (in Chinese), 2005, 48(3) :411-418
[6] 李立,金国元.攀西裂谷带及龙门山断裂带地壳上地幔的大地电磁测深研究.物探与化探,1987,11(3) :161-169 Li L, Jin G Y. Telluric electromagnetic sounding study of crust and upper mantle in the Panxi " Rift Zone" and the Longmen Shan faulted zone. Geophysical and Geochemical Exploration (in Chinese) , 1987, 11(3) :161-169
[7] 王运生,王绪本,苟量等.松潘-邵阳大地电磁剖面深、浅部典型构造的解释.南水北调与水利科技,2007,5(2) :70-77 Wang Y S, Wang X B, Gou L, et al. Several Progress of Deep-shallow Structure Interpretation by MT along Songpan-Shaoyang Cross Section. South-to-North Water Transfers and Water Science & Technology (in Chinese), 2007, 5(2) :70-77
[8] 王绪本,李永年,高永才.大地电磁测深二维地形影响及其校正方法研究.物探化探计算技术,1999,21(4) :328-332 Wang X B, Li Y N, Gao Y C. Two dimensional topographic responses in magneto telluric sounding and its correction methods. Computing Techniques for Geophysical and Geochemical Exploration (in Chinese) , 1999, 21(4) :328-332
[9] 赵国泽,汤吉,詹艳等.青藏高原东北缘地壳电性结构和地块变形关系的研究.中国科学(D辑),2004,34(10) :908-918 Zhao G Z, Tang J, Zhan Y, et al. Relation between electricity structure of the crust and deformation of crustal blocks on the northeastern margin of Qinghai-Tibet Plateau. Science in China (Ser. D) (in Chinese),2004,34(10) :908-918
[10] 赵国泽,陈小斌,王立凤等.青藏高原东边缘地壳“管流”层的电磁探测证据.科学通报,2008,53(3) :345-350 Zhao G Z, Chen X B, Wang L F, et al. Magnetotelluric evidence of the crustal 'channel flow' , the eastern Qinghai-Tibet Plateau. Chinese Science Bulletin (in Chinese), 2008, 53(3) :345-350
[11] 孙洁,晋光文,白登海等.青藏高原东缘地壳上地幔电性结构探测及其构造意义.中国科学(D辑),2003,33(增刊):173-180 Sun J, Jin G W, Bai D H, et al. Sounding of electrical structure of the crust and upper mantle along the eastern border of Qinghai-Xizang plateau and its tectonic significance. Science in China (D) (in Chinese), 2003,33(Suppl.):173-180
[12] 汤吉,詹艳,赵国泽等.青藏高原东北缘玛沁-兰州-靖边剖面地壳上地幔电性结构研究.地球物理学报,2005,48(5) :1205-1216 Tang J, Zhan Y, Zhao G Z, et al. Electrical conductivity structure of the crust and upper mantle along the profile Maqin-Lanzhou-Jingbian in the northeastern margin of the Qinghai-Tibet plateau. ChineseJ.Geophys.,(in Chinese), 2005,48(5) :1293-1306
[13] 马晓冰,孔祥儒,刘宏兵等.青藏高原东北部地区地壳电性结构特征.地球物理学报,2005,48(3) :689-697 Ma X B, Kong X R, Liu H B, et al. The electrical structure of northeastern Qinghai-Tibet plateau. Chinese J. Geophys. (in Chinese), 2005,48(3) :689-697
[14] 詹艳,赵国泽,王继军等.青藏高原东北缘海原弧形构造区地壳电性结构探测研究.地震学报,2005,27(4) :431-440 Zhan Y, Zhao G Z, Wang J J, Tang J, et al. Crustal electric structure of Haiyuan actuate tectonic region in the northeastern margin of Qinghai-Xizang plateau, China. Acta Seismologica Sinica (in Chinese), 2005, 27(4) :431-440
[15] 王绪本,余年,朱迎堂.龙门山逆冲构造带大地电磁测深初步成果.成都理工大学学报,2008,35(4) :398-403 Wang X B, Yu N, Zhu Y T , et al. Preliminary result of magnetotelluric sounding in the Longmenshan thrust belt of West Sichuan, China. Journal of Chengdu University of Technology (in Chinese) , 2008, 21(4) :398-403
[16] 王椿镛,吴建平,楼海.青藏高原东部壳幔速度结构和地幔变形场的研究.地学前缘,2006,13(5) :349-359 Wang C Y, Wu J P, Lou H. Study of crustal and upper mantle s structure and mantle deformation field beneath the eastern Tibetan plateau. Earth Science Frontiers ( in Chinese), 2006,13(5) :349-359
[17] Constable C S, Parker R L, Constable C G. Occam' s inversion: A practical algorithm for generating smooth models from electromagnetic sounding data. Geophysics, 1987,52:289-300
[18] William R, Randall L M. Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion. Geophysics, 2001,66(1) :174-187
[19] Burchfiel B C, Chen Z, Liu Y, et al. Tectonics of the Longmenshan and adjacent regions, Central China. International Geology Review, 1996, 37:661-735
[20] 崔作舟,陈纪平,吴苓.花石峡-邵阳深部地壳的结构和构造.北京:地质出版社,1996 Cui Z Z, Chen J P, Wu L. Texture and Structure of Huashixia-Shaoyang Deep Crust (in Chinese). Beijing: Geological Publishing House, 1996
[21] 郭正吾,邓康龄,韩永辉等.四川盆地形成与演化.北京:地质出版社,1996 Guo Z W, Deng K L, Han Y H, et al. Formation and Development of Sichuan Basin (in Chinese). Beijing:Geological Publishing House , 1996
[22] 殷鸿福,吴顺宝,杜远生等.华南是特提斯多岛洋体系的一部分.地球科学 中国地质大学,1999,24(1) :1-12 Yin H F, Wu S B, Du Y S, et al. South China defined as part of Tethyan archipelagic ocean system. Earth Science Journal of China University of Geosciences (in Chinese), 1999,24(1) :1-12
[23] 高锐,王海燕,马永生等.松潘地块若尔盖盆地与西秦岭造山带岩石圈尺度的构造关系-深地震反射剖面探测成果.地球学报,2006,27(5) :411-418 Gao R,Wang H Y, Ma Y S, et al. Tectonic relationships between the Zoige basin of the Songpan block and the west Qinling orogen at lithosphere scale: results of deep seismic reflection profiling. Acta Geoscientica Sinica (in Chinese), 2006, 27(5) : 411-418
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