I have good reason to expect
chunks of continental crust to be sitting in the Indian Ocean
and fairly large ones at that. The region
was a submergence zone on the rotational arc that I am most interested in and
cultural sources speak of land losses here even if the areal extent was far
from continental in size.
That such exist and that they are
also deep under water conforms with my expectations.
We obviously need to do a lot
more work here.
Parts of Gondwana megacontinent found off Australia
by Staff Writers
Sydney (AFP) Nov 17, 2011
Australian scientists exploring areas of the Indian
Ocean said Thursday they had found sunken parts of the
megacontinent Gondwana which could offer clues on how the current world was
formed.
The two "islands" were found on the remote sea floor in
international waters 1,600 kilometres (1,000 miles) west of Australia during a surveying trip
last month.
Their rocks contained fossils of creatures found in shallow waters,
meaning they were once part of the continent at or above sea level rather than
created by undersea volcanic activity, said Sydney University geophysicist Jo
Whittaker.
She called it an exciting discovery which would hopefully shed light on
how Gondwana broke into present-day Australia ,
Antarctica and India
between 80 and 130 million years ago.
Whittaker, one of the key researchers,
said she was particularly interested in exploring India's drift first northwest
and then sharply north, where its northeast coast, once joined to Australia,
smashed into Eurasia, forming the Himalayas .
"We have a fairly good idea where those continents were but we
don't exactly know, the eastern Indian Ocean is one of the more poorly explored
parts of the world's oceans in terms of tectonics," she told AFP.
"So it will help us figure out the plate kinematic motions that
led to India moving away
from Australia and heading
up off to crash into Eurasia ."
Samples of sandstone and granite dredged from a steep cliff on one of
the islands, about 2,000 metres (6,600 feet) below the ocean surface, are to be
dated but the research team
believe they are up to one billion years old.
The rocks will also be compared with samples from Australia 's west coast to try to
determine where exactly the islands broke away from.
Similar matching was not possible with India
because the relevant coast was now "smashed into the Himalayas
somewhere," said Whittaker.
She likened the continental separation to pulling something "a bit
gooey" apart and said the fragments, which are a fraction of the thickness
of normal continental crust and combined about the size of Scotland , were the "little
pieces that got left behind."
"These pieces are probably not as thick as (continental crust) so
they sit a little bit lower in the water, like something floating in the bath
essentially," she said.
Whittaker added that the fossil find was extremely lucky given the vastness
of the area they were dredging.
"We're excited to actually get some really good samples and
very clear cut continental rocks which show that (the islands)
are little fragments of Gondwana that were left behind as India moved away from
Australia," she said.
Plate tectonic theory is a relatively young science which was only
recognised in the 1950s and experts were still trying to establish what made
the continents move and change direction, she added.
Antarctica, on the other hand, was not moving at all and Whittaker said
discoveries like the Gondwana islands were critical.
"It's very significant, it's not every day you discover two large
continental fragments on the ocean floor," she said.
"Together with some of the other data this has the potential to
change how we've been modelling that part of the world and that
timeframe."
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