SA geoscientist discovers 'Lost Continent' after layover in Mauritius

2017-02-09 12:57 - Louzel Lombard Steyn
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Cape Town - We're learning something new about the planet we call home almost every day. And even as we speak, there are species of plants and animals that are completely unknown and still being discovered by humans. 

But to think that we've miscounted an entire continent when we first scanned the surface of the earth is quite ludicrous, really. That's Mother Nature for you - punching you in the gut as soon as you think you have the basics down. 

Here's the low-down: A new 'Lost Continent' has been discovered right underneath the island of Mauritius, captured in time beneath the waters of the Indian Ocean. But don’t start thinking about Atlantis myths. The new discovery documents a fragment of continent that was buried, rather than 'lost' per se' .

It's presumed the landmass was once part of a larger super-continent, but later fractured into ribbons. When, by chance, the volcanic eruption that created Mauritius occurred, about 9 million years ago, the fragment of continent was blanketed by lavas, and buried many kilometres below. 

The evidence is concrete: "Our findings confirm the existence of continental crust beneath Mauritius," the geo-scientists behind the discovery write in the publication on on Nature Communications

Understandably, the discovery is making waves around the world. And what makes it even greater, is that the discovery was led by a South-African based geoscientist, born in the US, who has lived and worked in SA since 1990.

Apart from discovering buried continents, Professor Lewis Ashwal is a lecturer at the University of Witwatersrand in Johannesburg. 

Prof Lewis D Ashwal in his office in the School of Geosciences, University of the Witwatersrand
Credit:  University of the Witwatersrand, Office of Communications

We caught up with the Prof to better understand the new discovery, and to dig a little deeper into other geological sites of interest. 

Traveller24: What first drew the attention of geologists and other scientists to the island of Mauritius? 

Professor Lewis Ashwal: Geologists have been studying Mauritius for a very long time, certainly since the 1930s, and probably before.  Much of the interest attempted to understand better the nature of the volcanic rocks, where and when they formed, etc.  

Our work in Mauritius, however, started by accident. We had been studying other Indian Ocean islands, including Madagascar and Seychelles, as well as India.  On a flight in maybe 2008 from Joburg to India, we had a layover in Mauritius, and instead of wasting time on the beach, we rented a car to look at the rocks and geology.  

On of our team members, Prof Bjorn Jamtveit, had the idea to collect some of the young lavas, to see if they might contain any old mineral grains, principally zircon.  

We are still not sure how and why he got this idea.  

Traveller24: When did you know you were onto something big? 

Professor Lewis Ashwal: Prof Jamtveit took the samples to Oslo, and surprisingly found some old zircons, with ages of about 250 million years. This cause a lot of excitement, but the grains turned out to be contamination from the crushing equipment that was used!

But he and other team members did not give up.  Instead of rock samples it was decided to collect beach sands, derived from erosion of the young volcanic rocks.  

No crushing equipment was needed for this test because Mother Nature had broken down the rocks for us. 

In two samples, old zircons were recovered, with ages of 660 – 1970 million years. There was a lot of scepticism and criticism from other geoscientists, who though that our zircons might have been transported by wind, or ocean currents, by vehicle tyres or footprints.  

To address the scepticism, I collected uncommon rocks called “trachytes” from Mauritius, for another project involving geochemistry.  

I noticed that these rocks contained high amounts of the element zirconium, which is an indicator of the presence of the mineral zircon. So, we analysed them and produced the spectacular result of old ages between 2 500 and 3 000 million years (there were also some young grains of about 6 million years, dating the time of formation of the trachyte hosts…). 

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.
Credit: Prof Susan J. Webb, University of the Witwatersrand

Lead author Prof. Lewis D Ashwal (left, red cap) sampling trachyte rocks in Mauritius. Such samples are about 6 million years old, but surprisingly contain zircon grains as old as 3000 million years. Colleague Dr Stephanie Werner (right, University of Oslo) is recording sample information.

Credit: Prof Susan J Webb, University of the Witwatersrand

Traveller24: Where was this 'buried' continent once situated before it disappeared, most likely? 

SEE: Quick Guide: Mauritius

Professor Lewis Ashwal: We suggest that the piece of continent buried below Mauritius, was at that time part of a larger continental entity that we named “Mauritia” in the 2013 paper.  

We think that other features in the Indian Ocean also represent continental fragments (including unfamiliar places like Saya de Malha, Chagos, Cargados-Carajos Banks, Laccadives, Nazareth Banks) that were then joined together to form Mauritia. 

They have since broken up and dispersed to their present positions.  We argue that at 85 – 90 million years ago, the continental entity of Mauritia must have been situated between Madagascar and India.  At that time, we estimate that Mauritia would have been about a third the size of Madagascar, or about 20 000 square kilometres.

Traveller24: Why was the continental crust ‘buried’ beneath the surface of the ocean? 

Professor Lewis Ashwal: Firstly, the continental crust never “sank”.  If anything, continental materials tend to “float”, because they are mainly composed of granites, which have lower density than the basaltic rocks in the ocean basins.  

The piece of continent we are talking about found itself, by chance, 9 million years ago, at a place where the new volcano of Mauritius decided to form.  The new lavas erupted onto, and blanketed this continental fragment, eventually burying to depths of several kilometres. 

Typical view of Mauritius beachfront with volcanic mountains in background. The basaltic lavas constituting these mountains formed no older than 9 million years ago.
Credit: Prof Susan J Webb, University of the Witwatersrand

Check out the video below to see an in-depth explanation from Prof Lewis Ashwal of the incredible discovery: 

Traveller24: What clues can visitors to the island of Mauritius look out for as evidence of the buried continent beneath the island?

Professor Lewis Ashwal: Regrettably, visitors to Mauritius will probably not be able to perceive any clues that there is a piece of continent below the volcano.  

Traveller24: Mauritius is obviously an ideal geological site of interest. What other places do you find of particular geological interest? 

Professor Lewis Ashwal: The Seychelles immediately comes to mind.  Here the rocks are granites, with ages around 750 million years.  The islands are also part of another old continental fragment, much of which is submerged but is estimated to presently be about 45 000 square kilometres in area.  

In the islands of the Seychelles, the ancient continental rocks are exposed at the surface and can be examined, studied and collected.  

Also, there are what I consider to be the best beaches in the world. 

SEE: Seychelles: Why it's good for the soul

At Réunion Island, again, one can possibly witness active volcanic eruptions.

This is the site of same the hot-spot that produced Mauritius 9 million years ago.  

Madagascar and India are much larger places where I have done lots of geological work. They are both unusual, interesting and wonderful places to visit.

Indian Ocean topography showing the location of Mauritius as part of a chain of progressively older volcanoes extending from the presently active hot-spot of Réunion toward the 65-million-year-old Deccan traps of northwest India.
Credit: Originally published in: Ashwal et al (2016) A mantle-derived origin for Mauritian trachytes. Journal of Petrology, vol. 57, pp. 1645-1675. Oxford University Press.

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