Johannesburg - A new study headed by Wits University geologist Professor Lewis Ashwal has confirmed the existence of a “lost continent” under Mauritius.
The study, “Archaean zircons in Miocene oceanic hot spot rocks establish ancient continental crust beneath Mauritius”, was published in the prestigious journal Nature Communications.
“We are studying the break-up process of the continents in order to understand the geological history of the planet,” said Ashwal, who is the lead author on the paper.
He explained that this “lost continent” was left over from the break-up of the super-continent, which started about 200 million years ago.
Gondwanaland existed more than 200 million years ago and contained rocks as old as 3.6 billion years, before it split up into what are now the continents of Africa, South America, Antarctica and Australia, as well as India.
“The piece of crust under Mauritius, which was subsequently covered by young lava during volcanic eruptions on the island, seems to be a tiny piece of ancient continent, which broke off from the island of Madagascar when Africa, India, Australia and Antarctica split up and formed the Indian Ocean,” Ashwal said.
Wits geologist Professor Lewis Ashwal points out the location of a ‘lost continent' in the Indian Ocean. Picture: YouTube / Wits University
The discovery was made through studying the mineral zircon, which is found in rocks spewed up by lava during volcanic eruptions.
Ashwal and his colleagues, Dr Michael Wiedenbeck, from the German Research Centre for Geosciences (GFZ), and Trond Torsvik, from the University of Oslo, who is a guest scientist at GFZ, found that the remnants of this mineral were far too old to belong on the island of Mauritius.
“Earth is made up of two parts: continents, which are old, and oceans, which are ‘young’. On the continents you find rocks that are over 4 billion years old, but you find nothing like that in the oceans, as this is where
new rocks are formed,” said Ashwal.
“Mauritius is an island, and there is no rock older than 9 million years old on the island. However, by studying the rocks on the island, we have found zircons that are as old as 3 billion years,” he said.
“Zircons are minerals that occur mainly in granites from the continents. They contain trace amounts of uranium, thorium and lead, and due to the fact that they survive geological process very well, they contain a rich record of geological processes and can be dated extremely accurately,” Ashwal said.
The geologists have found that zircons of this age prove there are much older crustal materials under Mauritius that could only have originated from a continent.
He said this was not the first time that zircons that were billions of years old had been found on the island. A study done in 2013 has found traces of the mineral in beach sand. However, this study received some criticism, including 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 corroborates the previous study and refutes any suggestion of wind-blown, wave-transported or pumice-rafted zircons for explaining the earlier results,” Ashwal stressed.
He proposed that there may be many more pieces of various sizes of “undiscovered continent”, collectively called “Mauritia”.
“These pieces are spread across the Indian Ocean, left over by the break-up of Gondwanaland.
“According to the new results, this break-up did not involve a simple splitting of the ancient supercontinent of Gondwana, but rather, a complex splintering took place, with fragments of continental crust of variable sizes left adrift within the evolving Indian Ocean basin,” he concluded.
Known as a tropical holiday destination, Mauritius is a volcanic island, formed by the eruption of volcanoes starting at about 9 million years ago.