History

The Existence of a ‘Lost Continent’ Under Mauritius Confirmed

Gondwanaland

Gondwanaland is a super continent that existed more than 200 million years ago. It contained rocks as old as 3.6 billion years old before it split up into what are now the continents of South America, Africa, India, Australia and Antarctica. The break-up happened because of the geological process of plate tectonics. The ocean basin is in motion continuously and moves between 2 cm and 11 cm per year. Continents move because they ride on the plates that make up the ocean floor.

When Gondwanaland started breaking up about 200 million years ago, a “lost continent” was left over under the Indian Ocean island of Mauritius. Scientists have now confirmed the existence of this continent. The piece of crust seems to be a small piece of the ancient continent, which broke off from the island of Madagascar, when India, Africa, Antarctica and Australia split up and formed the Indian Ocean. The piece was subsequently covered by young lava during volcanic eruptions on Madagascar.

alkali crystal
Different sized crystals of alkali feldspar like the large white one at lower left are aligned by magmatic flow. A large zircon crystal appears as the brightly coloured grain just right of centre. Image Credit: Wits University

Professor Lewis Ashwal is a Wits geologist and lead author on the paper titled “Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius”. The paper was published in the prestigious journal Nature Communications. Ashwal explained that in order to understand the geological history of the planet, scientists are studying the break-up process of the continents.

Ashwal and his colleagues Trond Torsvik from the University of Oslo and Michael Wiedenbeck from the German Research Centre for Geosciences (GFZ) studied the mineral zircon that is found in rocks spewed up by lava during volcanic eruptions and found that fragments of zircon were much too old to belong on the island of Mauritius.

lost continent
Indian Ocean topography marking the location of Mauritius as part of a chain of progressively older volcanoes spreading from the presently active hot-spot of Réunion toward the 65-million-year-old Deccan traps of northwest India. Credit: Wits University

Ashwal explained that earth is made up of two parts – oceans, which are relatively young, and continents, which are much older. Rocks that are over four billion years old can be found on the continents, but not in the oceans, as this is where new rocks are formed. Mauritius is an island and the rocks on it are no older than 9 million years. Ashwal and his colleagues studied the rocks on the island and found zircons that are up to 3 billion years old in the rocks.

Zircons occur mainly in granites from the continents and contain trace amounts of uranium, lead and thorium. They survive geological process very well and therefore contain a rich record of geological processes that can be dated extremely accurately. Ashwal noted that the fact that they found zircons that are so old proves that there are much older crustal materials under Mauritius. These materials could only have originated from a continent.

Zircons that are billions of years old have been found on the island before. In a study done in 2013, traces of the mineral was found in beach sand. This study did however receive some criticism, as the mineral could have been blown in by the wind, or carried in on scientists’ shoes or vehicle tires. Ashwal added that since they found the ancient zircons in 6 million year old rock (trachyte), the previous study has been corroborated, and any suggestion of wave-transported, wind-blown, or pumice-rafted zircons has been thoroughly refuted.

Gondwana
Lead author Prof. Lewis D. Ashwal studying an outcropping of trachyte rocks in Mauritius. Samples are about 6 million years old, but remarkably contain zircon grains as old as 3000 million years. Credit: Susan Webb/Wits University

Ashwal concluded by stating that there are many pieces of various sizes of the undiscovered continent spread over the Indian Ocean, These pieces are collectively called “Mauritia” and were left over by the breaking up of Gondwanaland. Based on the new results, this breakup did not involve a simple splitting of the ancient super continent of Gondwanaland. It now seems that a complex splintering took place with fragments of continental crust of different sizes let loose within the ever-evolving Indian Ocean basin.

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