龙门山中段构造特征与汶川地震
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摘要
通过地表地质调查、钻井资料和各种地球物理资料分析,剖析了龙门山中段的构造特征和岩石圈结构特征的特殊性:(1)10 Ma以来龙门山中段隆升幅度和速率最大;(2)龙门山中北段喜马拉雅期构造活动较南段弱;(3)龙门山中段主构造带之下存在有大于10 000Ω.m的高阻异常体;(4)龙门山中段具有+0.015 cm/s2的剩余(60 km×60 km~120 km×120 km)布格重力异常;(5)龙门山中段为正的均衡重力异常区。在此基础上,结合汶川地震主震和余震的分布特征,得出:(1)四川汶川地震主震和绝大多数余震震源多位于映秀-北川主断层下盘(扬子地块上),断层活动的主动盘是下盘,映秀-北川主断层的活动为俯冲兼左旋走滑;(2)此次地震是扬子板块向西俯冲(L型俯冲)、四川盆地顺时针旋转和青藏高原隆升逆冲相互作用的产物;(3)四川汶川地震有可能是构造地震的一种新类型,其孕育巨大能量的最重要条件为地块坚硬(能量不易释放)和位于地块边缘(构造作用强烈,有能量来源)。最后,建议有关部门和地学界重视中国主要地块边缘的重力场,尤其是剩余布格异常和均衡重力异常的研究。这也许对地震的长期预测有所帮助。
The central Longmen Mountains has special structural features and lithospheric structure based on field geology,drilling data and geophysical data.The central Longmen Mountains has the fastest uplift rate and highest uplift scope in ～10 Ma.The central-northern parts of Longmen Mountains have weaker tectonic activities than the southern part during Himalayan period.There is a high resistive anomalous body(>10 000 Ω·m),a +0.015 cm/s2 residual Bouguer gravity anomaly(60 km×60 km~120 km ×120 km) and a positive isostatic gravity anomaly in the central Longmen Mountains.Comparing the distribution features of the epicenters of the Wenchuan main and aftershocks and the structural features in Longmen Mountains,the hypocenters of the Wenchuan main and aftershocks are located in the active footwall(on the Yangtze Block) of the Yingxiu-Beichuan main fault.The footwall subducts to the eastern Himalaya plateau margin with sinistral strike-slip.The Wenchuan earthquake occurred as a result of the synthesis of the L-type subduction of Yangtze Block,the clockwise rotation of Sichuan Basin and the thrust and uplift in Qinghai-Tibet Plateau.The Wenchuan earthquake is probably a new-typed tectonic earthquake locating on the margin of a stiff block.The authors suggest that more attention should be paid to the gravity field on the margins of main blocks in our country,especially the residual Bouguer gravity anomaly and isostastic gravity anomaly.
The central Longmen Mountains has special structural features and lithospheric structure based on field geology,drilling data and geophysical data.The central Longmen Mountains has the fastest uplift rate and highest uplift scope in ～10 Ma.The central-northern parts of Longmen Mountains have weaker tectonic activities than the southern part during Himalayan period.There is a high resistive anomalous body(>10 000 Ω·m),a +0.015 cm/s2 residual Bouguer gravity anomaly(60 km×60 km~120 km ×120 km) and a positive isostatic gravity anomaly in the central Longmen Mountains.Comparing the distribution features of the epicenters of the Wenchuan main and aftershocks and the structural features in Longmen Mountains,the hypocenters of the Wenchuan main and aftershocks are located in the active footwall(on the Yangtze Block) of the Yingxiu-Beichuan main fault.The footwall subducts to the eastern Himalaya plateau margin with sinistral strike-slip.The Wenchuan earthquake occurred as a result of the synthesis of the L-type subduction of Yangtze Block,the clockwise rotation of Sichuan Basin and the thrust and uplift in Qinghai-Tibet Plateau.The Wenchuan earthquake is probably a new-typed tectonic earthquake locating on the margin of a stiff block.The authors suggest that more attention should be paid to the gravity field on the margins of main blocks in our country,especially the residual Bouguer gravity anomaly and isostastic gravity anomaly.
引文
[1]刘树根.龙门山冲断带与川西前陆盆地的形成演化[M].成都:成都科技大学出版社,1993.
[2]罗志立,龙学明.龙门山造山带崛起和川西前陆盆地沉降[J].四川地质学报,1992,12(1):1-17.
[3]周荣军,李勇,DENSMORE A L,等.青藏高原东缘活动构造[J].矿物岩石,2006,26(2):40-51.
[4]安其美,丁立丰,王海忠,等.龙门山断裂带的性质与活动性研究[J].大地测量与地球动力学,2004,24(2):115-119.
[5]贾东,陈竹新,贾承造,等.龙门山前陆褶皱冲断带构造解析与川西前陆盆地的发育[J].高校地质学报,2003,9(3):402-410.
[6]龙学明.龙门山中北段地史发展的若干问题[J].成都地质学院学报,1991,18(1):8-15.
[7]邓康龄.龙门山构造带印支期构造递进变形与变形时序[J].石油与天然气地质,2007,28(4):485-490.
[8]刘树根,罗志立,赵锡奎,等.中国西部盆山系统的耦合关系及其动力学模式以龙门山造山带-川西前陆盆地系统为例[J].地质学报,2003,77(2):177-186.
[9]陈社发,邓起东,赵小麟,等.龙门山中段推覆构造带及相关的演化历史和变形机制(一)[J].地震地质,1994,16(4):405-412.
[10]刘树根,罗志立,戴苏兰,等.龙门山冲断带的隆升和川西前陆盆地的沉降[J].地质学报,1995,69(3):205-214.
[11]周建文,曾庆,徐世琦,等.龙门山北段推覆构造带变形特征研究[J].天然气工业,2005,25(增刊A):66-71.
[12]马永旺,王国芝,胡新伟,等.“彭灌杂岩”推覆体的构造变形特征[J].四川地质学报,1996,16(2):110-114.
[13]林茂炳,苟宗海,王国芝,等.四川龙门山造山带造山模式研究[M].成都:成都科技大学出版社,1996.
[14]林茂炳,马永旺.论龙门山彭灌杂岩体的构造属性[J].成都理工学院学报,1995,22(1):42-46.
[15]唐荣昌,黄祖智,钱洪,等.成都断陷区活动断裂带基本特征及其潜在地震能力的判定[J].中国地震,1996,12(3):285-293.
[16]刘树根,罗志立,宋鸿彪,等.四川龙门山冲断带中北段岩石圈结构研究[J].石油与天然气地质,1990,11(1):86-95.
[17]刘树根,罗志立,曹树恒.四川龙门山冲断带(中北段)岩石圈的层圈性和多级滑脱推覆[J].四川地质学报,1990,10(3):145-150.
[18]钱迈平,厉建华,孙万铨,等.三叠纪扬子板块的漂移导致下扬子区石膏、硬石膏矿床的形成[J].江苏地质,2002,26(3):129-134.
[19]刘育燕,杨巍然,森永速男,等.华北陆块、秦岭地块和扬子陆块构造演化的古地磁证据[J].地质科技情报,1993,12(4):17-21.
[20]王二七,孟庆任,陈智,等.龙门山断裂带印支期左旋走滑运动及其大地构造成因[J].地学前缘,2001,8(2):375-384.
[21]刘树根,罗志立,赵锡奎,等.龙门山造山带-川西前陆盆地系统形成的动力学模式及模拟研究[J].石油实验地质,2003,25(5):432-438.
[2]罗志立,龙学明.龙门山造山带崛起和川西前陆盆地沉降[J].四川地质学报,1992,12(1):1-17.
[3]周荣军,李勇,DENSMORE A L,等.青藏高原东缘活动构造[J].矿物岩石,2006,26(2):40-51.
[4]安其美,丁立丰,王海忠,等.龙门山断裂带的性质与活动性研究[J].大地测量与地球动力学,2004,24(2):115-119.
[5]贾东,陈竹新,贾承造,等.龙门山前陆褶皱冲断带构造解析与川西前陆盆地的发育[J].高校地质学报,2003,9(3):402-410.
[6]龙学明.龙门山中北段地史发展的若干问题[J].成都地质学院学报,1991,18(1):8-15.
[7]邓康龄.龙门山构造带印支期构造递进变形与变形时序[J].石油与天然气地质,2007,28(4):485-490.
[8]刘树根,罗志立,赵锡奎,等.中国西部盆山系统的耦合关系及其动力学模式以龙门山造山带-川西前陆盆地系统为例[J].地质学报,2003,77(2):177-186.
[9]陈社发,邓起东,赵小麟,等.龙门山中段推覆构造带及相关的演化历史和变形机制(一)[J].地震地质,1994,16(4):405-412.
[10]刘树根,罗志立,戴苏兰,等.龙门山冲断带的隆升和川西前陆盆地的沉降[J].地质学报,1995,69(3):205-214.
[11]周建文,曾庆,徐世琦,等.龙门山北段推覆构造带变形特征研究[J].天然气工业,2005,25(增刊A):66-71.
[12]马永旺,王国芝,胡新伟,等.“彭灌杂岩”推覆体的构造变形特征[J].四川地质学报,1996,16(2):110-114.
[13]林茂炳,苟宗海,王国芝,等.四川龙门山造山带造山模式研究[M].成都:成都科技大学出版社,1996.
[14]林茂炳,马永旺.论龙门山彭灌杂岩体的构造属性[J].成都理工学院学报,1995,22(1):42-46.
[15]唐荣昌,黄祖智,钱洪,等.成都断陷区活动断裂带基本特征及其潜在地震能力的判定[J].中国地震,1996,12(3):285-293.
[16]刘树根,罗志立,宋鸿彪,等.四川龙门山冲断带中北段岩石圈结构研究[J].石油与天然气地质,1990,11(1):86-95.
[17]刘树根,罗志立,曹树恒.四川龙门山冲断带(中北段)岩石圈的层圈性和多级滑脱推覆[J].四川地质学报,1990,10(3):145-150.
[18]钱迈平,厉建华,孙万铨,等.三叠纪扬子板块的漂移导致下扬子区石膏、硬石膏矿床的形成[J].江苏地质,2002,26(3):129-134.
[19]刘育燕,杨巍然,森永速男,等.华北陆块、秦岭地块和扬子陆块构造演化的古地磁证据[J].地质科技情报,1993,12(4):17-21.
[20]王二七,孟庆任,陈智,等.龙门山断裂带印支期左旋走滑运动及其大地构造成因[J].地学前缘,2001,8(2):375-384.
[21]刘树根,罗志立,赵锡奎,等.龙门山造山带-川西前陆盆地系统形成的动力学模式及模拟研究[J].石油实验地质,2003,25(5):432-438.
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