The real extent of the Indian Plate
Part of the Indian Plate that originally broke away from the Gondwana supercontinent is now subducted under the Himalayas and the Tibetan Plateau. A new paleogeographic reconstruction now reveals its true size.
Hundreds of millions of years ago, the surface of the Earth looked very different from the world that is familiar to us today. There were just two continents – Laurasia and Gondwanaland. What is now the Indian subcontinent was part of Gondwanaland, which itself broke up about 150 million years ago. One of the pieces became the Indian Plate. “Paleogeographic reconstructions suggest that the northernmost segment of the Indian Plate was originally much larger, but has since been subducted under the Asian Plate. This lost landmass is known to geologists as Greater India. The question of how much of the Indian Plate’s lithosphere (the outermost layer of the Earth) has been lost to subduction has an important bearing on how the Tibetan Plateau was formed as a result of the collision between India and Asia,” says Professor Stuart A. Gilder of LMU’s Geophysics Institute. However, estimates of the extent of Greater India have remained very uncertain. “These estimates vary between a few hundred and more than 2000 kilometers.”
In collaboration with colleagues from the Chinese University of Geosciences in Beijing, Gilder has obtained new paleomagnetic data which allowed them to track the geographical position of the northern sector of the Indian Plate through time. This then allowed the authors to calculate a minimum size for Greater India. “Our data show that the area of lithosphere consumed by subduction since the onset of the collision about 55 million years ago was larger than the surface area of the Indian subcontinent today. This confirms that, in the Cenozoic, the rise of the Tibetan Plateau was driven by the addition of buoyant subducted material to its base. Our data makes it possible to define how much of the lithosphere of the Indian Plate has been lost since the break-up of Gondwana.” The study suggests that Greater India corresponds to a wedge-shaped segment of the original Indian Plate, which can now be traced some 2500 km to the north toward its western edge and approximately 2000 km at its eastern limit. Consequently, almost 5 million km² of lithosphere has been subducted under the Asian Plate. (Geophysical Research Letters 2019)