Ocean sank 1,100 km into earth, raising chain of volcanic islands

March 6th, 2009 - 11:49 am ICT by IANS  

Sydney, March 6 (IANS) Researchers have discovered how an entire ocean destroyed itself 50 to 20 million years ago when its floor sank 1,100 km into the earth between Australia and New Zealand.
Using new computer modelling programmes, Monash University geoscientist Wouter Schellart was able to reconstruct the resulting cataclysm when the ocean’s tectonic plate sank into the earth’s interior, forming a long chain of volcanic islands at the surface.

Researchers think that this chain of volcanic islands formed a geographical connection between New Caledonia and New Zealand. Schellart conducted the research,

“In our latest research we show for the first time evidence for such a connection by combining reconstructions of the tectonic plates that cover the earth’s surface with seismic tomography, a technique that allows one to look deep into the earth’s interior,” Schellart said.

“This technique uses seismic waves that travel through the Earth’s interior to map regions of high velocity versus regions with low velocity. Regions with a high velocity are thought to represent tectonic plates that have disappeared (subducted) into the earth’s interior,” Schellart said.

“We are able to say the ocean basin was approximately four km deep and so contained four km of water, while the tectonic plate (which includes the ocean floor) that underlies the four km of water was on average 70 km thick. The ocean basin was originally some 2,500 km by 700 km in lateral extent, so this means that the “plate” of 2,500 km by 700 km by 70 km sank into the earth’s interior,” he said, according to a Monash release.

“We then searched deep within the Earth for evidence of such a connection using seismic tomography and found the evidence at 1,100 km depth below the Tasman Sea in the form of a subducted tectonic plate,” Schellart said.

These findings were published in Earth and Planetary Science Letters, in collaboration with Brian Kennett from Australian National University, Canberra, and Wim Spakman and Maisha Amaru from Utrecht University in the Netherlands.

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