At the end of the Cretaceous Period (145 to 66 million years ago), India accelerated its course northward into Eurasia by 20 million years. What for ? Together with several colleagues, Oliver Jagoutz from MIT (Massachusetts Institute of Technology) provided a new explanation: the phenomenon of double subduction (the diving of one plate under another plate) occurred more than 80 million years ago. plate.

Some mechanisms, such as thrust forces generated by rising mantle at a hot spot, can explain accelerated tectonic movements. However, none produced an acceleration of more than one to two million years. To support the hypothesis of a double subduction mechanism, Oliver Jagoutz's team first determined the possible position of this tectonic system based on the geological traces of the disappearance of Neo-Thethis (an ancient lost ocean located in East Africa). Then the researchers carried out a digital simulation of the operation of this system using two different methods.

According to their scenario, around 90 million years ago, subduction of the Neo-Thethys plate (which became the Indian plate) beneath the Ksirhoda plate (a lost tectonic plate located north of Neo-Thethis) began to approach the Ksirhoda plate. under Eurasia. Since then, a kind of east-west oriented “pipe” has formed between the two diving plates, from which the upper ductile mantle must exit as the two subduction zones approach each other.

Initially not very sensitive, this phenomenon will accelerate after 70 million years, when the distance between the two subduction zones becomes small enough. Indeed, numerical simulations show that the length of this “pipe” decreases as the Indian plate advances and reduces the length of this “pipe”, which accelerates the flow of evacuated material, due to the resistance of the viscous “wall”. which becomes shorter, becomes smaller. This mechanism will facilitate the rapprochement of the two subduction zones. The result: The Indian Plate accelerated northward for 20 million years.

Reference

Oliver Jagoutz, et al., Very rapid convergence of India and Eurasia via double subduction, Natural Geosciences, flight. 8, p. 475-478, 2015.

Magali Billen, Double dip, Natural Geosciences, flight. 8, p. 428-429, 2015.

M. Fournier and N. Chamot-Rooke, The Birth of the Ocean, For scienceNo.390, April 2010.