Why India broke off from supercontinent

Last Updated: Wednesday, November 16, 2011 - 14:13

Melbourne: Scientists claim to have
discovered two huge sunken islands in the Indian Ocean, which
once formed part of the last link between India and Australia.

A team from Sydney University, Macquarie University and
the University of Tasmania say the two islands, about the size
of Tasmania, were once part of the supercontinent Gondwana and
are more than 1.5 kilometres underwater.

They say the islands, discovered west of Australia, were
once above water. The discovery was made while the scientists
were mapping the seafloor of the Perth Abyssal Plain.

"The data collected on the voyage could significantly
change our understanding of the way in which India, Australia
and Antarctica broke off from Gondwana," University of Sydney
geologist Dr Joanne Whittaker, a team member, said.

The scientists returned to Perth last week after
carrying out the complicated task of dredging up hundreds of
kilogrammes of rock samples from the steep slopes of the two
islands during a three-week expedition aboard a vessel.

Travelling on the Southern Surveyor, they discovered the
islands through detailed seafloor mapping and by dredging rock
samples from the steep slopes of the two islands, now in water
depths of over 1.5 kilometres, the Australian media reported.

"We expected to see common oceanic rocks such as basalt
in the dredge, but were surprised to see continental rocks
such as granite, gneiss and sandstone containing fossils," Dr
Simon Williams, the chief scientist on the expedition, said.

He added: "A detailed analysis of the rocks dredged up
during the voyage will tell us about their age and how they
fit into the Gondwana jigsaw."

The islands, called "micro continents", were formed when
India began to move away from Australia, 130 million years ago
during the Cretaceous period, when dinosaurs roamed the Earth.

They became stranded thousands of kilometres from either coast
as the land masses separated, say the scientists.

"The sunken islands charted during the expedition have
flat tops, which indicates they were once at sea level before
being gradually submerged.

"Our preliminary analysis of the magnetic data that we
collected could cause us to rethink the plate tectonic story
for the whole of the Eastern Indian Ocean," Dr Whittaker said.

PTI



First Published: Wednesday, November 16, 2011 - 13:01

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