The holiday islands of Reunion and Mauritius are all that remains of a small continent that's been hidden under lava for millions of years.
The land mass, dubbed Mauritia, detached about 60 million years ago while Madagascar and India drifted apart.
Such micro-continents in the oceans seem to occur more frequently than previously thought, says a new study in Nature Geoscience. Mantle plumes, giant bubbles of hot rock, rise from the deep mantle and soften tectonic plates from below, until they break apart at the hotspots.
If the zone of the rupture lies at the edge of a land mass, fragments of the land mass can become separated off. The Seychelles are a well-known example of such a continental fragment, splitting from Madagascar/India.
And plumes now underneath the islands of Marion and Reunion appear to have played a role in the emergence of the Indian Ocean, with a study of lava sand grains from Mauritius indicating the existence of further fragments.
The sand grains contain semi-precious zircons aged between 660 and 1970 million years, dropped there by the lava as it pushed through the continental crust. To confirm the dating, the team recalculated plate tectonics to explain exactly how and where the fragments ended up in the Indian Ocean.
"On the one hand, it shows the position of the plates relative to the two hotspots at the time of the rupture, which points towards a causal relation," says Dr Bernhard Steinberger of the GFZ German Research Centre for Geosciences.
"On the other hand, we were able to show that the continent fragments continued to wander almost exactly over the Reunion plume, which explains how they were covered by volcanic rock."