Abstract:

The collision between the Indian and Asian plates uplifted the Himalayan-Tibetan Plateau, thickening and expanding the crust. The deep structure of the plateau-a scientific mystery of global concern-can reveal how the two continents collide and how the collision deforms the continent. One of the most effective ways to unlock this scientific mystery is deep seismic reflection profiling. For more than 20 years using this technology we have detected the fine structure of the thick crust of the Tibetan Plateau, overcoming the technical bottleneck of accessing the lower crust and the Moho and revealing the intracontinental collision process. Based on the research results, this paper systematically summarizes the deep behavior of the collision and subduction between the Indian and Asian plates under the Tibetan Plateau, on topics ranging from the NS-EW correlation to the plateau’s hinterland. The deep behavior includes the underthrusting of the Indian crust beneath the Himalayan orogenic belt on the southern margin of the plateau, the subduction of the lithosphere of the Alashan block in the Asian plate under the Qilian mountain in the northern rim of the plateau, the outward crustal extension in the Qilian mountain range, and the face-to-face collision between the Tarim block and the West Kunlun in the northwestern margin of the plateau; in the eastern margin of the plateau it was discovered that the Longriba fault, not the Longmenshan fault, is the western border fault of the Yangtze plate. In the plateau’s hinterland the Moho lines are thin and flat and lithosphere extension collapses. Multiple deep reflection profiles reveal the collisional behavior of the Indian and Asian plates under the Yalungzangbo suture zone. The subduction of the Indian continental crust varies from east to west, and the crust travels northward to different locations inside the Lhasa terrain. In the central suture zone, the upper and lower parts of the Indian crust become detached as the upper crust overthrusts while the lower crust subducts northward. During the subduction, material return and structural superposition cause the thinning and thickening of the Indian and Himalayan crust, respectively. The leading edge of the subducting Indian crust collides with the Asian crust and sinks into the mantle, while a near-vertical collision occurs between the Gangdise at the leading edge of the Asian plate, and the Tethys. Together, the partial melting of the lower crust of the Gangdise, the seismic data that show near transparent weak reflection and localized bright spot reflection, and the near-flat Moho, all reflect the extensional tectonic environment of the southern margin of the Asian plate.

Key words: Himalayan-Tibetan Plateau, continent-continent collision, continental underthrust, deep process, deep seismic reflection profile