The beaches of Mauritius contain fragments of a type of rock typical of ancient continental crust — rock which could have been brought to the surface by volcanic eruptions.
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The drowned remnants of an ancient microcontinent may lie scattered beneath the waters between Madagascar and India, a new study suggests.
Evidence for the long-lost land comes from Mauritius, a volcanic island about 900 kilometers east of Madagascar. The oldest basalts on the island date to about 8.9 million years ago, says Bjørn Jamtveit, a geologist at the University of Oslo. Yet grain-by-grain analyses of beach sand that Jamtveit and his colleagues collected at two sites on the Mauritian coast revealed around 20 zircons — tiny crystals of zirconium silicate that are exceedingly resistant to erosion or chemical change — that were far older.
The zircons had crystallized within granites or other igneous rocks at least 660 million years ago, says Jamtveit. One of these zircons was at least 1.97 billion years old.
Jamtveit and his colleagues suggest that rocks containing the wayfaring zircons originated in ancient fragments of continental crust located beneath Mauritius. They propose that geologically recent volcanic eruptions brought shards of the crust to Earth’s surface, where the zircons eroded from their parent rocks to pepper the island’s sands. The team's work is published today in Nature Geoscience.
Crustal remains
The paper also suggests that not just one but many fragments of continental crust lie beneath the floor of the Indian Ocean. Analyses of Earth’s gravitational field reveal several broad areas where sea-floor crust is much thicker than normal — at least 25 to 30 kilometers thick, rather than the normal 5 to 10 kilometers.
Those crustal anomalies may be the remains of a landmass that the team has dubbed Mauritia, which they suggest split from Madagascar when tectonic rifting and sea-floor spreading sent the Indian subcontinent surging northeast millions of years ago. Subsequent stretching and thinning of the region’s crust sank the fragments of Mauritia, which together had comprised an island or archipelago about three times the size of Crete, the researchers estimate.
The team chose to collect sand, rather than pulverize local rocks, to ensure that zircons inadvertently trapped in rock-crushing equipment from previous studies did not contaminate their fresh samples. The nearest known outcrop of continental crust that could have produced the Mauritian zircons is on Madagascar, far across a deep sea, Jamtveit notes. Furthermore, the zircons came from Mauritian sites so remote that it is unlikely that humans carried them there.
“There’s no obvious local source for these zircons,” says Conall Mac Niocaill, a geologist at the University of Oxford, UK, who was not involved in the research.
Also, it does not seem as if the zircons rode to Mauritius on the wind, says Robert Duncan, a marine geologist at Oregon State University in Corvallis. “There’s a remote possibility that they were wind blown, but they’re probably too large to have done so,” he adds.
Other ocean basins worldwide may well host similarly submerged remains of “ghost continents”, Mac Niocaill notes in an accompanying News & Views article. Only detailed surveys of the ocean floor, including geochemical analyses of their rocks, will reveal whether the splintered and now submerged Mauritia has any long-lost cousins, he suggests.
This article is reproduced with permission from the magazine Nature. The article was first published on February 24, 2013.
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7 Comments
Add CommentBruceGrande............................what crap is this ?
Reply | Report Abuse | Link to thisThe whole World was probably completely covered with a "crust." Now, when I cook something and its is boiling and then starts too cool, I get a layer covering the top surface of the pot. So, assuming there is enough mass to the Earth which I think there is, when the Earth was molten and as it started to cool there was a "crust" covering the entire World. Just through randomness, I would think that certain areas of the Earth were hotter than other areas, so it had some separation of the "crust." Then, all the plate tectonic stuff separated the continents ... blah, blah, blah ...
Reply | Report Abuse | Link to thiswhat happens if you all ready knew this information? Does this mean that Scientific America should give me a job? I'm no geologist but looking at google earth it seems very very obvious that there was a continent there. Just to save you some research money.....when the "Mauritia" went underwater, it made the water table raise approx. 100-400 ft. so really all you have to do is look off the edge of each continent approx. 100-400 feet out to sea and you'll find all kind of ancient civilizations. It's really simple, give me a job and I'll find them for you!!!!
Reply | Report Abuse | Link to thisMicrocontinent? So an island, then?
Reply | Report Abuse | Link to thisI read about this a little earlier in the 'regular' news. What I was hoping for was a somewhat more scientific explanation of what this micro-continent was. In my albeit limited knowledge of what continents are in general, I have to assume that what is implied is that the micro-continent Mauritia comprised shield areas of continental crust, or some elements of craton... right?
Reply | Report Abuse | Link to thisIt's obviously one of those work from home scams. My advise is to not click on the link. Treat these postings as spam and report them to SA as an abuse posting.
Reply | Report Abuse | Link to thisYou are correct - you aren't a geologist. Your lack of understanding of the basics of science is pretty obvious from just your short little post. With plate tectonics some plates are lifted as they ride over other plates that are thus subducted. Civilizations on subducting plates do indeed get flooded out but it isn't due to an increase in water level. It is due to a change in elevation. Water level only changes in response to ice accretion or melting.
Reply | Report Abuse | Link to thisPerhaps instead of displaying your ignorance you may want to take even just a few minutes and try learning something.