Abstract
The southern boundary between India and the Tibetan Plateau represents
a classical case of continental subduction, where the Indian continental
lithosphere is subducted northwards beneath the Tibetan Plateau.
At the northern boundary, southward subduction of Asian lithosphere
beneath the Tibetan Plateau has also been proposed, but imaging has
been hampered by inadequate data quality. Here we analyse the plate
tectonic structure of the northern boundary between Tibet and Asia
using the S receiver function technique. Our passive source seismic
data build on, and extend further northwards, the existing geophysical
data from the International Deep Profiling of Tibet and the Himalaya
project. We detect, beneath central and northern Tibet, a relatively
thin, but separate, Tibetan lithosphere overriding the flat, southward
subducting Asian lithosphere. We suggest that this overriding Tibetan
lithosphere helps to accommodate the convergence between India and
Asia in central and northern Tibet. We conclude that the Tibetan-Himalayan
system is composed of three major parts: the Indian, Asian and Tibetan
lithospheres. In the south, the Indian lithosphere underthrusts Tibet.
In central and northern Tibet a separate, thin Tibetan lithosphere
exists, which is underthrust by the Asian lithosphere from the north.
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