Tectonic uplift in Himalaya led to formation of 'steep' gorge

A team of researchers has discovered a canyon, filled with more than 500 m of sediments beneath the bed of the present-day Yarlung Tsangpo River upstream from the gorge.

A team of German, Chinese, and American geoscientists were able to reconstruct the former valley floor of this river with the help of drill cores which allowed them to reconstruct the geological history of the Tsangpo Gorge.

The geoscientists discovered that the gorge obtained its steep form in response to rapid tectonic uplift in the Himalaya, two to three million years ago.

Dirk Scherler from the GFZ German Research Centre for Geosciences, said that because of its high gradient, the river incised its bed very rapidly and the rocks here were eroded at annual rates of up to one centimeter per year which was matched by tectonic uplift of the same rate and the collision of India with the Eurasian continent had created a tectonic dam here.

Dirk Scherler said that one of the drillings encountered bedrock after 540 meters of sediments and from the drill cores, they were able to infer the reduction in stream flow velocity and date the initiation of sedimentation using cosmogenic nuclides and these were rare isotopes that were produced by cosmic rays near the Earth's surface.

The new findings showed that rapid incision of the Yarlung Tsangpo and the development of the Tsangpo Gorge occurred in response to tectonic uplift, and not, as previously thought, the other way round. In addition, these observations refute existing hypotheses that relate the origin of the Tsangpo Gorge to river capture of the Yarlung Tsangpo by the Brahmaputra River.