The breakup of Gondwana, the southern supercontinent, began about 200 million years ago. Map: University of the Witwatersrand
The existence of “Mauritia", a “lost continent" from the Gondwana in the Indian Ocean underneath the island of Mauritius, has been established by researchers from the University of the Witwatersrand in South Africa.
The lava-covered piece of continent is a remnant from the breakup of the Gondwana, the southern supercontinent which began some 200 million years ago, the University said in a release published on EurekAlert.
The research of geology professor Lewis Ashwal has discovered that zirkons on the Island of Mauritius date back some 3 billion years ago, to what was one of the Earth’s earliest periods, whereas other rocks on the island only go back to 9 million years ago.
Gondwana: The Parent
According to the research findings, the piece of crust, which was covered by young lava from volcanic eruptions on Mauritius later on, constitutes a particle of an ancient continent, which broke off from the island of Madagascar, when Africa, India, Australia and Antarctica split up from supercontinent Gondwana (or Gondwanaland) and formed the Indian Ocean.
The release reminds that Gondwanaland was a supercontinent that existed more than 200 million years ago and contained rocks as old as 3.6 billion years.
Its splitting up into what are now the continents of Africa, South America, Antarctica, India and Australia occurred because of the geological process of plate tectonics, the continuous motion of the ocean basin by between 2 cm and 11 cm per year.
It is also pointed out that Mauritius is a volcanic island formed by the eruption of volcanoes starting about 9 million years ago.
Mauritius itself is a part of a string of islands, formed by a stationary hotspot, a volcano presently found at Reunion Island, a territory of France. The hotspot remains stationary as the oceanic tectonic plates move across it thus creating a string of volcanic islands.
“We are studying the breakup process of the continents, in order to understand the geological history of the planet,” says Wits geologist, Professor Lewis Ashwal, who is the lead author on the paper entitled “Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius”, published in the Nature Communications journal.
Zircon Secrets Revealed
Researching zircon, the mineral found in rocks spewed up by lava during volcanic eruptions, Ashwal and his colleagues Michael Wiedenbeck from the German Research Center for Geosciences (GFZ) and Trond Torsvik from the University of Oslo, guest scientist at GFZ, have established that the zircon remnants found on the island of Mauritious are too old to belong to it.
“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 explains.
“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 elaborates.
Zircons are minerals that occur mainly in granites from the continents, and contain trace amounts of uranium, thorium and lead. Since they survive geological processes very well, they contain a rich record of these processes and can be dated with high accuracy, the researchers noted.
lead author Prof. Lewis D. Ashwal studying an outcropping of trachyte rocks in Mauritius. Such samples are about 6 million years old, but surprisingly contain zircon grains as old as 3000 million years. Photo: Susan Webb/Wits University
“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,” Ashwal concludes.
The researchers point out that this was not the first time that billion-year-old zircons had been found on Mauritius.
Back in 2013, a study discovered zircon traces in beach sand. However, the significance of the discovery was questioned, including with arguments that the mineral could have been blown in by the wind, or brought in on vehicle tyres or scientists’ shoes.
“The fact that we found the ancient zircons in rock (6-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,” says Ashwal.
The geologist believes that numerous pieces of varied size of the “undiscovered continent”, collectively called “Mauritia”, which are left over from the breakup of Gondwanaland, can be identified all over what is today the Indian Ocean.
“According to the new results, this break-up did not involve a simple splitting of the ancient super-continent 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,” Ashwal explains.