A study headed up by a Wits University geologist has confirmed the existence of a “lost continent” under the island of Mauritius.
Professor Lewis Ashwal is the lead author of the paper: Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius.
His study showed that the newly discovered lava-covered piece of continent is an ancient remnant, left over from the break-up of the supercontinent, Gondwana, which existed about 200 million years ago.
The piece of crust, 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 the Indian Ocean was formed.
Ashwal said his team was studying the break-up process of the continents in order to understand the geological history of the planet.
By studying zircon, the mineral found in rocks spewed up by lava during volcanic eruptions, Ashwal and his colleagues Michael Wiedenbeck from the German Research Centre for Geosciences (GFZ) and Trond Torsvik from the University of Oslo found that remnants of this mineral were far too old to belong to 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 four billion years old, but you find nothing like that in the oceans, as this is where new rocks are formed,” Ashwal said.
Ashwal said that Mauritius is an island with no rock older than nine million years old. However, by studying the rocks on the island, his team found zircons that are 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 only have originated from a continent,” said Ashwal.
Zircons are minerals that occur mainly in granites from the continents. They contain trace amounts of uranium, thorium and lead. Because they survive geological processes very well, they contain a rich record of those processes and can be dated extremely accurately.
This is not the first time that zircons that are 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 criticism with claims 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 said.
Ashwal suggested that there are many pieces of various sizes of “undiscovered continent”, collectively called “Mauritia”, spread over the Indian Ocean, left over by the breakup of Gondwanaland.