Deep seismic reflection in himalaya reqion reveals the complexity of the crust and upper mantle structure

The abrupt rise of Himalaya and the uplift of the Qinghai-Tibet plateau are considered as the consequence of convergence, collision and compression between Indian and Asian plates since Mesozoic and Cenozoic. The results of the first deep seismic reflection survey in Himalayan mountain area are reported here. The test profile is located within North Himalaya region, from Pagri, to the south of the Himalayan crest, to Samada, to the south of Kangmar. On the CMP stacked section the following features are observed: 1. a mid-crustal strong reflection zone, that extends as far as 100 km and more, dipping gently to the north; it probably represents an active thrust or a huge decollement zone, along which the intact Indian crust or its lower crust underthrusts beneath southern Tibet; 2. an abundance of reflections in the upper crust, indicating occurrence of large-scale imbrications in it; 3. the reflection of the lower crust suggesting some plastic-rlieological features; 4.a distinct Moho reflection in the Southern Part of the profile at a depth of about 72-75km and an additional secondary Moho in the south; 5. a series of north-dipping reflections of large extension acquired from beneath Moho at 32s, 36s, 48s of TWTT with abundant information, which may reflect the stratification and deformation features of the upper mantle. All these results give substantial support to such views that the intact Indian continental crust or its lower part underthrusts South-Tibetan Tethys-Himalayan crust, resulting in thickening of the southernmost Tibetan crust.