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By Charles Q. Choi, OurAmazingPlanet Contributor | LiveScience.com – 7 hrs ago



This map shows the thickness of the crust around the Mauritius and Reunion Island region. The circled numbers note how many millions of years ago the mantle plume there was beneath or near the Indian and African tectonic plates.



The remains of a micro-continent scientist call Mauritia might be preserved under huge amounts of ancient lava beneath the Indian Ocean, a new analysis of island sands in the area suggests.

These findings hint that such micro-continents may have occurred more frequently than previously thought, the scientists who conducted the study, detailed online Feb. 24 in the journal Nature Geoscience, say.


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Digging in the sand

The beach sands of Mauritius are the eroded remnants of volcanic rocks created by eruptions 9 million years ago. Collecting them"was actually quite pleasant," said researcher Ebbe Hartz, a geologistat the University of Oslo in Norway. He described walking out from a tropical beach, "maybe with a Coke and an icebox, and you dig down underwater into sand dunes at low tide."

Within these sands, investigators discovered about 20 ancient zircon grains (a type of mineral) between 660 million and 1,970 million years old. To learn more about the source of this ancient zircon, the scientists investigated satellite maps of Earth's gravity field. The strength of the field depends on Earth's mass, and since the planet's mass is not spread evenly, its gravity field is stronger in some places on the planet's surface and weaker in others.

The researchers discovered Mauritius is part of a contiguous block of abnormally thick crust that extends in an arc northward to the Seychelles islands. The finding suggests Mauritius and the adjacent region overlie an ancient micro-continent they call Mauritia. The ancient zircons they unearthed are shards of lost Mauritia.

The researchers meticulously sought to rule out any chance these ancient grains were contaminants from elsewhere.

"Zircons are heavy minerals, and the uranium and lead elements used to date the ages of these zircons are extraordinarily heavy, so these grains do not easily fly around — they did not blow into Mauritius from a sandstorm in Africa," Hartz told OurAmazingPlanet.

"We also chose a beach where there was no construction whatsoever — that these grains did not come from cement somewhere else," Hartz added. "We were also careful that all the equipment we used to collect the minerals was new, that this was the first time it was used, that there was no previous rock sticking to it from elsewhere."

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Ancient Lost Continent Discovered in Indian Ocean

Landmass "drowned" during continental breakup about 85 million years ago.



Lion Mountain (pictured) is located in southeastern Mauritius.
Photograph by Danita Delimont, Alamy


by Ker Than
for National Geographic News
Published February 25, 2013


Evidence of a drowned "microcontinent" has been found in sand grains from the beaches of a small Indian Ocean island, scientists say.

A well-known tourist destination, Mauritius is located about 1,200 miles (2,000 kilometers) off the coast of Africa, east of Madagascar. Scientists think the tiny island formed some nine million years ago from cooling lava spewed by undersea volcanoes.

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Prehistoric Atlantis

Jamtveit and his colleagues estimate that the lost microcontinent, which they have dubbed Mauritia, was about a quarter of the size of Madagascar.

Furthermore, based on a recalculation of how the ancient continents drifted apart, the scientists concluded that Mauritia was once a tiny part of a much larger "supercontinent" that included India and Madagascar, called Rodinia.

The three landmasses "were tucked together in one big continent prior to the formation of the Indian Ocean," Jamtveit said.

But like a prehistoric Atlantis, Mauritia was eventually drowned beneath the waves when India broke apart from Madagascar about 85 million years ago.

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Missing Evidence?

Jérôme Dyment, a geologist at the Paris Institute of Earth Physics in France, said he's unconvinced by the work because it's possible that the ancient zircons found their way to the island by other means, for example as part of ship ballast or modern construction material.

"Extraordinary claims require extraordinary evidence, which are not given by the authors so far," said Dyment, who did not participate in the research.

"Finding zircons in sand is one thing, finding them within a rock is another one ... Finding the enclave of deep rocks that, according to the author's inference, bring them to the surface during an eruption would be much more convincing evidence."

Dyment added that if Mauritia was real, evidence for its existence should be found as part of a joint French and German experiment that installed deep-sea seismometers to investigate Earth's mantle around Réunion Island, which is situated about 120 miles (200 kilometers) from Mauritius.

"If a microcontinent lies under Réunion, it should be depicted by this experiment," said Dyment, who is part of the project, dubbed RHUM-RUM.

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In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era. It formed at ~1.0 Ga by accretion and collision of fragments produced by breakup of the older supercontinent, Columbia, which was assembled by global-scale 2.0-1.8 Ga collisional events. Rodinia has entered popular consciousness as one of the two great supercontinents of earth history, the other being Pangaea. --Wiki


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Prehistoric supercontinents


    Gondwana (~510–~180 million years ago)

    Laurasia (~510–~200 million years ago)

    Pangaea (~300–~200 million years ago)

    Euramerica (~300 million years ago)

    Oldredia (~418–~380 million years ago)

    Pannotia, also called Vendian (~600–~540 million years ago)

    Rodinia (~1.1 Ga–~750 million years ago)

    Columbia, also called Nuna (~1.8–1.5 Ga ago)

    Nena (~1.8 Ga)

    Kenorland (~2.7 Ga ago). Neoarchean sanukitoid cratons and new continental crust formed Kenorland. Protracted tectonic magna plume rifting occurred 2.48 to 2.45 Ga and this contributed to the Paleoproterozoic glacial events in 2.45 to 2.22 Ga. Final breakup occurred ~2.1 Ga.

    Ur (~3 Ga ago). Classified as the earliest known landmass. Ur, however, was probably the largest, perhaps even the only continent three billion years ago. While probably not a supercontinent, one can argue that Ur was a supercontinent for its time, even if it was smaller than Australia is today. Still, an older rock formation now located in Greenland dates back from Hadean times.

    Vaalbara (~3.6 Ga ago). Evidence is the Yilgarn Craton, Western Australia and the worldwide Archean greenstone belts that were subsequently spread out across Gondwana and Laurasia. --Wiki


N.B. Ga = one billion years (thousand million years)

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