Underwater 'ghost continent' discovered through beach crystals
After combing through grains of sand on a beach -- literally -- scientists have announced that there is an undiscovered "ghost" micro-continent sitting below the Indian Ocean, according to a new study in Nature Geoscience.
Norwegian geologists collected sand from remote beaches on the coast of Mauritius, a tiny island in the Indian Ocean between Africa, India, and Australia.
Mauritius is a volcanic island, and the oldest basalts (volcanic rocks) found there are 8.9 million years old. But the researchers sifting through beach sand discovered 20 zircons, or tiny crystals, that were much older and had formed inside granite, a different kind of rock. Most of the zircons had crystallized 660 million years ago; one zircon was 1.97 billion years old.
Where did these mystery crystals come from?
The nearest continental crust that could have produced the zircons is Madasgascar, 1,100 kilometres to the east across a deep sea. The researchers say it's unlikely the zircons drifted that far, or were blown there by winds. It's also unlikely humans carried them, since the beaches are so remote.
Their theory: the rock matter bubbled up on volcanic plumes from a sunken piece of continental shelf -- a ghost micro-continent -- sitting below the Indian Ocean, and eventually washed up on Mauritius.
The geologists also say the sea-floor crust is much thicker than it should be in this area: 25 to 30 kilometers thick, rather than the usual five to 10. That leads them to believe a piece of continental shelf three times the size of Crete sank below the sea when the shifting of tectonic plates split India off of Africa and sent it northeast.
Geochemical analysis of the rocks below the sea near Mauritius will help resolve this theory and answer the question of whether more lost continents lie beneath the ocean.
Kate Allen is the Star's science and technology reporter. Find her on Twitter: @katecallen