Himalayan continental collision began 52 million years ago

Thorough and precise PhD research corrects for previous pitfalls

Wentao Huang
Wentao Huang

The timing of the collision of continents of the Asian and Indian plates, which marked the start of the formation of the Himalayan mountain range, has been subject to much discussion in geology. PhD research by Utrecht University’s Wentao Huang has found that this began some 52 million years ago. Huang will defend his PhD thesis in the University Hall at 10.30 on 24 April. 

Deduced from historical positions 

The Tibetan Plateau and the Himalayas form the largest mountain range in the world and are the result of a collision of continental blocks connected to the Indian and Asian plates. The Tibetan Plateau is the ‘crumple zone’ of the Asian Plate, while the Himalayan mountain range can be seen as a huge peel-off and pile-up of the Indian Plate’s crust, as a result of the collision. 

Determining exactly when the collision history began is crucial for accurately calculating the speed and causes of the mountain range’s formation, with the key being the palaeogeographical locations of two geological blocks: the Lhasa Block, situated along the southern edge of Asia in present-day Tibet, and the Tethyan Himalayan Block, the northernmost continental crust that was attached to the Indian Plate.

Wentao Huang

Measuring magnetic orientation

One of the most accurate ways to determine the timing of the collision is by using the remanent magnetisation preserved in magnetic minerals in rocks magnetised at the time of their formation. ‘The magnetisation dip angle varies with latitude; it is vertical at the poles and horizontal at the equator,’ explains Huang. ‘India travelled northward towards Asia and, by measuring remanent magnetisation in samples of continental rocks of different ages from the Indian and Asian plates, we were able to determine the latitudes at which these continents were located over the course of time. Identical palaeolatitudes measured in same-age rock samples from the two continents reveal the collision moment.’

Although this technique has been applied for many years, previous results were very variable and could not be explained. This in turn led to major disputes about the timing of the collision and even about the number of continental blocks that fused into the Himalayas.

Causes of uncertainty

Huang’s second PhD supervisor, Dr Douwe van Hinsbergen, is very impressed by the thoroughness of the candidate’s work. ‘Wentao carried out very extensive and detailed magnetic research on rock samples from the two blocks,’ Van Hinsbergen explains. ‘He shows in his thesis that resetting of the magnetic signal is a much underrated cause of the spread in palaeolatitude estimates. Resetting can be caused by groundwater flowing through the rocks, for instance. Another important reason is deformation of the magnetic field by increasing compaction – as a result of burial by younger rocks – of the rock that contains the magnetic marker.’

52 million years ago

Huang was aware of and corrected for these pitfalls, thus achieving a consistent latitude for the first collision of approximately 20 degrees North. The first overlapping latitudes for the Indian and Asian continental blocks occurred 52 million years ago.

Main Indian continent came later

Huang was also able to confirm that although the Tethyan Himalayan block was part of the Indian Plate at the time of its collision with Asia, it must have been separated from the main Indian continent by a large oceanic domain that formed sometime between 116 and 68 million years ago. It was not until much later, probably some 25 million years ago, that the main Indian continent collided with Asia.

The Indan and Asian plates started moving towards each other, and met about 52 million years ago. A block from the Indian plate collided with the continental block of the Asian plate, and formed the Himalayas.

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