Investigation of the deep geophysical structure of the Longmen Mountains tectonic belt and its relation to the Wenchuan Earthquake is important for the study of earthquakes.By using magnetotelluric sounding profiles o...Investigation of the deep geophysical structure of the Longmen Mountains tectonic belt and its relation to the Wenchuan Earthquake is important for the study of earthquakes.By using magnetotelluric sounding profiles of the Luqu-Zhongjiang and Anxian-Suining; seismic sounding profiles of the Sichuan Maowen-Chongqing Gongtan,the Qinghai Huashi Gorge-Sichuan Jianyang,and the Batang-Zizhong; and magnetogravimetric data of the Longmen Mountains region,the deep geophysical structure of the Songpan-Ganzi block,the western Sichuan foreland basin,and the Longmen Mountains tectonic belt and their relation was discussed.The eastward extrusion of the Qinghai-Tibet Plateau thrusts the Songpan-Ganzi block upon the Yangtze block,which obstructs the eastward movement of the Qinghai-Tibet Plateau.The Maoxian-Wenchuan,Beichuan-Yingxiu,and Anxian-Guanxian faults of the Longmen Mountains fault belt dip to northwest with different dip angles and gradually converge in the deeper parts.Geophysical structure suggests that an intracrustal low-velocity,low-resistivity,and high-conductivity layer is common between the middle and upper crust west of the Longmen Mountains tectonic belt but not in the upper Yangtze block.The Sichuan Basin has a thick low-resistance sedimentary layer on a stable high-resistance basement; moreover,there are secondary paleohighs and depression structures at the lower part of the western Sichuan foreland basin with characteristic of high magnetic anomalies,whereas the Songpan-Ganzi block has a high resisitivity cover of upper crust and continues to a low-resistance layer.Considering the Longmen Mountains tectonic belt as the boundary,there are Bouguer gravity anomalies of ＂one belt between two zones.＂ Thus,we infer that there is a corresponding relation between the inferred crystalline basement of the Songpan block and the underlying basin basement of the Longmen Mountains fault belt.Furthermore,there may be an extensive ancient Yangtze block,which is west of the Ruoergai block.In addition,the crust-mantle ductile shear zone under the Longmen Mountains tectonic belt is the main fault,whereas the Beichuan-Yingxiu and Anxian-Guanxian faults at the surface are earthquake faults.The Wenchuan Ms 8.0 earthquake might be attributed to the collision of the Yangtze block and the Qinghai-Tibet Plateau.The eastward obduction of the eastern edge of the Qinghai-Tibet Plateau and eastward subduction of its deeper part under the influence of the collision of the Indian,Pacific,and Philippine Plates with the Eurasia Plate might have caused the Longmen Mountains tectonic belt to cut the Moho and extend to the middle and upper crust; thus,creating high stress concentration and rapid energy release zone.展开更多
Based on the studies of geology and geochemistry, A’nymaque—Mianlue limited oceanic basin is comparable to the Paleo\|Tethys on time, sedimentary, biocoenosis, and the type of ophiolite (Coleman, 1984; Deng, 1984; X...Based on the studies of geology and geochemistry, A’nymaque—Mianlue limited oceanic basin is comparable to the Paleo\|Tethys on time, sedimentary, biocoenosis, and the type of ophiolite (Coleman, 1984; Deng, 1984; Xu, 1996;Chenliang, 1999). The A’nyemaqen—Mianlue oceanic basin was one of a northeast branches of Paleo\|Tethys (Zhang Guowei, 1995; 1996) .Our researches on deformations reveal that tectonic styles of the Southwest Qinling orogenic belt is obviously influenced by the dynamics of Qinghai—Tibet plateau.Structural deformation analysis suggested that the southwest part of Qinling have undergone 3 major deformation stages in Mesozoic and Cenozoic. Firstly, rock folding at deep\|middle tectonic level and progressively thrusting shearing characterized the deformation of collision. The thrust tectonics are south\|directed, such as A’nymaque, Wenxian—Kangxian and Mianlue thrusting systems, and the deformations took place in T\-2—T\-3. Secondly, the middle\|tectonic level thrusting and sinistral strike\|slip formed at early intracontinental period (J—K), the thrust tectonics was south\|directed and the regional penetrative left\|lateral slips were NW or NWW. Finally, the east\|west extensional deformations which occurred in late Mesozoic and Cenozoic, a series of north\|south directing basins came into being in this stage, Huixian—Chengxian basin and Lixian basin for example, which overlapped the former deformation styles.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 40839909, No. 41274077 and No. 41274078)
文摘Investigation of the deep geophysical structure of the Longmen Mountains tectonic belt and its relation to the Wenchuan Earthquake is important for the study of earthquakes.By using magnetotelluric sounding profiles of the Luqu-Zhongjiang and Anxian-Suining; seismic sounding profiles of the Sichuan Maowen-Chongqing Gongtan,the Qinghai Huashi Gorge-Sichuan Jianyang,and the Batang-Zizhong; and magnetogravimetric data of the Longmen Mountains region,the deep geophysical structure of the Songpan-Ganzi block,the western Sichuan foreland basin,and the Longmen Mountains tectonic belt and their relation was discussed.The eastward extrusion of the Qinghai-Tibet Plateau thrusts the Songpan-Ganzi block upon the Yangtze block,which obstructs the eastward movement of the Qinghai-Tibet Plateau.The Maoxian-Wenchuan,Beichuan-Yingxiu,and Anxian-Guanxian faults of the Longmen Mountains fault belt dip to northwest with different dip angles and gradually converge in the deeper parts.Geophysical structure suggests that an intracrustal low-velocity,low-resistivity,and high-conductivity layer is common between the middle and upper crust west of the Longmen Mountains tectonic belt but not in the upper Yangtze block.The Sichuan Basin has a thick low-resistance sedimentary layer on a stable high-resistance basement; moreover,there are secondary paleohighs and depression structures at the lower part of the western Sichuan foreland basin with characteristic of high magnetic anomalies,whereas the Songpan-Ganzi block has a high resisitivity cover of upper crust and continues to a low-resistance layer.Considering the Longmen Mountains tectonic belt as the boundary,there are Bouguer gravity anomalies of ＂one belt between two zones.＂ Thus,we infer that there is a corresponding relation between the inferred crystalline basement of the Songpan block and the underlying basin basement of the Longmen Mountains fault belt.Furthermore,there may be an extensive ancient Yangtze block,which is west of the Ruoergai block.In addition,the crust-mantle ductile shear zone under the Longmen Mountains tectonic belt is the main fault,whereas the Beichuan-Yingxiu and Anxian-Guanxian faults at the surface are earthquake faults.The Wenchuan Ms 8.0 earthquake might be attributed to the collision of the Yangtze block and the Qinghai-Tibet Plateau.The eastward obduction of the eastern edge of the Qinghai-Tibet Plateau and eastward subduction of its deeper part under the influence of the collision of the Indian,Pacific,and Philippine Plates with the Eurasia Plate might have caused the Longmen Mountains tectonic belt to cut the Moho and extend to the middle and upper crust; thus,creating high stress concentration and rapid energy release zone.
文摘Based on the studies of geology and geochemistry, A’nymaque—Mianlue limited oceanic basin is comparable to the Paleo\|Tethys on time, sedimentary, biocoenosis, and the type of ophiolite (Coleman, 1984; Deng, 1984; Xu, 1996;Chenliang, 1999). The A’nyemaqen—Mianlue oceanic basin was one of a northeast branches of Paleo\|Tethys (Zhang Guowei, 1995; 1996) .Our researches on deformations reveal that tectonic styles of the Southwest Qinling orogenic belt is obviously influenced by the dynamics of Qinghai—Tibet plateau.Structural deformation analysis suggested that the southwest part of Qinling have undergone 3 major deformation stages in Mesozoic and Cenozoic. Firstly, rock folding at deep\|middle tectonic level and progressively thrusting shearing characterized the deformation of collision. The thrust tectonics are south\|directed, such as A’nymaque, Wenxian—Kangxian and Mianlue thrusting systems, and the deformations took place in T\-2—T\-3. Secondly, the middle\|tectonic level thrusting and sinistral strike\|slip formed at early intracontinental period (J—K), the thrust tectonics was south\|directed and the regional penetrative left\|lateral slips were NW or NWW. Finally, the east\|west extensional deformations which occurred in late Mesozoic and Cenozoic, a series of north\|south directing basins came into being in this stage, Huixian—Chengxian basin and Lixian basin for example, which overlapped the former deformation styles.
