CRUSTAL STRUCTURE OF THE TIBETAN PLATEAU AND SURROUNDING AREA

In the early Cretaceous (140 Ma), after the break up of Pangea, the Indian and Eurasian plates began moving towards one another. Initially the movement was accommodated by subduction of oceanic crust and a series of non-terminal collisions with microplates and arcs. Eventually, at approximately 45 Ma the terminal suture of India and Eurasia began. Since then, the plates have moved a further 2000 -3000 km together. Scientists are still uncertain as to how and where this crust has been accommodated. Geological and geophysical data should enable us to answer this and other questions governing the behavior of the continental crust and deformation processes in operation.

This project aims to answer some of these questions, including: How is the 2000+ km of crust accommodated? How has the Tibetan Plateau reached its current height? How has the surrounding area been deformed?

In order to answer these questions and investigate the crustal structure of the area, two datasets have been examined. The first is a deep seismic profile running northeast across the northeastern flank of the Tibetan Plateau and into the Ordos Block, part of the Sino-Korean Terrain. The profile is modeled using the reflectivity method. The second dataset compiles existing data points that comprise velocity-depth information for mid-Asia.

We found that the crust increases in thickness from 40km in surrounding areas, to 60km under Tibet. Beneath the Tibetan Plateau p is lower than under the surrounding areas and global averages. The upper crust is much thicker than normal (between 40% and 100% thicker). There is no increase in lower crustal thickness, in places there is no crust with 'normal' lower crustal velocities. The Moho is a complex interface, suggestive of an undulating boundary. Thickness changes are more sudden along the southern margin of the plateau