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Scientists ‘discover’ ancient continental crust beneath Mauritius

17th February 2017

By: Donna Slater

Features Deputy Editor and Chief Photographer

     

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The tropical volcanic island of Mauritius has been found to be hiding fragments of an ancient continent and the secrets of how the earth was formed about 200-million years ago when the supercontinent – Gondwana – broke up, according to University of the Witwatersrand (Wits) geologist Professor Lewis Ashwal.

He conveyed the findings as lead author in a paper titled ‘Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius’, which was published by open-access journal Nature Communications.

Ashwal and a team of fellow scientists have confirmed the existence of such a “lost continent” under the Indian Ocean island of Mauritius after the supercontinent broke up. According to Ashwal’s findings, the piece of crust, which was subsequently covered by ‘young’ lava during volcanic eruptions on the island, seems to be a tiny piece of this ancient megacontinent, which broke off from the island of Madagascar when Africa, India, Australia and Antarctica split into landmasses, leaving a void, which is now the Indian Ocean.

Working on the paper with colleagues, Michael Wiedenbeck, of the German Research Centre for Geosciences (GFZ), and Trond Torsvik, of the University of Oslo, Ashwal explains that the discovery was made during their study of the break-up process of the continents, which was undertaken to better understand the geological history of earth.

By studying a mineral – zircon – found in rocks spewed up by lava during volcanic eruptions, Ashwal and his colleagues determined that remnants of this mineral were far too old to have come from the island of Mauritius.

Zircon is a mineral that is found mainly in granites from the continents. The mineral contains trace amounts of uranium, thorium and lead, and, owing to its ability to survive geological processes, it contains a rich record of such processes and can be dated with precise accuracy.

Earth comprises continents, which are old, and oceans, which are young, says Ashwal. The continents have rocks that are more than four- billion years old; however, “you find nothing like that in the oceans, as this is where new rocks are formed”, he adds.

Ashwal points out that Mauritius is an island with no rocks older than nine-million years, but studying the rocks revealed the existence of zircons as old as three-billion years: “The fact that we have found zircons of this age proves that there are much older crustal materials under Mauritius that could have originated only from a continent.”

This is not the first time that zircons, billions of years old, have been found on the island. A study done in 2013 found traces of the mineral in beach sand. However, this study received some criticism, which included that the mineral could have been either blown in by the wind or carried in on vehicle tyres or scientists’ shoes.

“The fact that we found the ancient zircons in rock (six-million-year-old trachyte), corroborates the previous study and refutes any suggestion of wind-blown, wave-transported or pumice-rafted zircons for explaining the earlier results,” he assures.

Further, Ashwal suggests that many pieces of various sizes of “undiscovered continent” – collectively called Mauritia – are spread over the Indian Ocean because of Gondwanaland having broken up into various other continents.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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