Scientists find two 'sunken islands' off WA - part of Gondwana land link
- From: PerthNow
- November 14, 2011
SCIENTISTS have discovered two huge sunken islands in the Indian Ocean west of Perth.
The islands, about the size of Tasmania, were once part of the supercontinent Gondwana and are more than 1.5km underwater.
Researchers from the University of Sydney, Macquarie University and the University of Tasmania say the islands were once above water and formed part of the last link between India and Australia.
They made the discovery while 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 said.
The scientists returned to Perth last week after carrying out the complicated task of dredging up hundreds of kilograms of rock samples from the steep slopes of the two islands during a three-week expedition aboard CSIRO vessel Southern Surveyor.
“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,” University of Sydney’s chief expedition scientist Dr Simon Williams said.
“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, about 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, the scientists say.
“The sunken islands charted during the expedition have flat tops, which indicates they were once at sea level before being gradually submerged,” Dr Whittaker said.
“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,” she said.