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Microplate Discovery Dates Birth of Himalayas

The discovery of the first oceanic microplate in the Indian Ocean is helping an international team of scientists to identify when the initial collision between India and Eurasia led to the birth of the Himalayas.

At least seven microplates are known in the Pacific Ocean, but this is the first ancient Indian Ocean microplate discovered. Radar beam images from an orbiting satellite have helped put together pieces of this plate tectonic jigsaw and pinpointed the age for the collision, whose precise date has divided scientists for decades.

Reported in Earth and Planetary Science Letters (tinyurl.com/onutrlv), the team believes the collision occurred 47 million years ago when India and Eurasia initially smashed into each other.

“The age of the largest continental collision on Earth has long been controversial, with age estimates ranging from at least 59 to 34 million years ago,” said lead author Dr Kara Matthews of The University of Sydney. “Knowing this age is particularly important for understanding the link between the growth of mountain belts and major climate change.”

The researchers discovered that crustal stresses caused by the initial collision cracked the Antarctic Plate far away from the collisional zone and broke off a fragment the size of Tasmania in a remote patch of the central Indian Ocean. The authors have named this the Mammerickx Microplate after Dr Jacqueline Mammerickx, a pioneer in seafloor mapping.

Rotation of the Mammerickx Microplate is revealed by a rotating pattern of grooves and hills that turn the topography of the ocean floor into a jagged landscape. These “abyssal hills” record a sudden increase in crustal stress that date the birth of the Himalayan mountains to 47 million years ago.

The new research shows that 50 million years ago, India was travelling northwards at speeds of 15 cm/year. Soon after it slammed into Eurasia, crustal stresses along the mid-ocean ridge between India and Antarctica intensified to breaking point. A chunk of Antarctica’s crust broke off and started rotating like a ball bearing, creating the Mammerickx Microplate.