A Passive Seismological Profile Experiment In Eastern Margin Of Tibetan Plateau And Longmen-Shan Region

The knowledge about the formation,the evolution and the dynamic of the Tibetan plateau is deeply linked to the results obtained through numerous seismological campains in this region since more than 30 years. These seismological experiments yield a better knowledge of the structure and composition of the crust and upper mantle in central Tibet. Nevertheless only the eastern border of the plateau,constituted by the Longmen-Shan belt tend towards NE that separates the Tibetan plateau from the Yangtze craton,has never been studied in detail since 2005.A passive seismological experiment profile across the Longmen-Shan belt to Songpan-Ganzi block,deployed from the front range up to the inside of the plateau and for more than one year period. It will help us to know about the property of the Longmen-Shan belt.With the appearance and development of the portable,agile, high accuracy full spectrum seismograph,we can utilize the broadband and three-component seismograph to study the structure and composition of the crust and upper mantle. It opened the new way for the Earth deep structure research, impelled the global deep structure as well as the Earth dynamics research enormously. And with the data incrsasing and the use of the new method, the receive function method already became effective method to study lithosphere mantle speed structure and the speed surface of discontinuity. Therefore this article studied specifically the formation,the evolution and the dynamic of the eastern border of the Tibetan plateau and Longmen-Shan through the receive function method.We use the teleseismic receiver function method to invert the image of crustal and lithospheric structure ,The depth of Moho boundary is increased from 36～40KM in Yangtze craton,50KM across the Longmen-Shan belt,and 62～65KM in the central part of Songpan-Ganzi block. However it shows across the Xushuihe fault zone. The depth of boundary between the lithosphere and astheosphere is 140~150KM. The lithosphere structure and dynamics process is very greatly different in Eastern Margin of Tibetan Plateau(Longmen-Shan)and southern Margin of Tibetan Plateau(the Himalaya Mountains) and northern Margin of Tibetan Plateau(Kunlun Mountain).There are both intracontinental subduction of lithospheric plate in Southern Margin of Tibetan Plateau and Northern Margin of Tibetan Plateau, Especially the southern margin of the Indian plate under the lithosphere can plug into more than 100 kilometres depth, the level of over a distance of several hundred to more than 1,000 kilometers.The mosaic relations of Eastern Margin of Tibetan Plateau and the Yangtze block is completely different, It isn't still founded within the lithosphere of the land diving, the two plots of the lithosphere along Longmenshan, Minshan inlay to the vicinity of the collision with its depth From 150km (Yangtze block) to 160～170km (Eastern Margin of Tibetan Plateau).The napping of the upper part of Longmenshan is the main role of forming a series of reversed faults, large-scale complex rock mass and klippes. It's caused by the role of Songpan Ganzi block in the upper crust along the low-speed Layer(slip surface) thrust to the surface. The Nappe of the Longmenshan is mainly formatted in the Mesozoic Jurassic, but it has been greatly weakened since the new generation.