[ASC-media] Media Release: Maiden voyage to find lost volcanoes

Leharne.Fountain at ga.gov.au Leharne.Fountain at ga.gov.au
Wed Feb 19 17:30:55 EST 2003

Geoscience Australia and
University of Tasmania
Media Release 
19 February 2003
Maiden voyage to find lost volcanoes
Australia's newest research vessel Southern Surveyor, will be christened today for its maiden expedition to find lost volcanoes in the Norfolk Basin area, east of Australia. 

Seven scientists from the University of Tasmania and Geoscience Australia will embark from Hobart for a month-long marine geoscience study, partly funded by the Australian Research Council, to investigate the 100 million year-old volcanism thought to exist on the Lord Howe and Norfolk Ridges off Australia's eastern coast.

"We know explosive volcanoes formed along eastern Australia, because of the thick volcanic sediments found in basins further west, such as those in Bass Strait, and as shown by our plate tectonic studies", says Expedition Chief Scientist Professor Tony Crawford, from the Centre for Ore Deposit Research at the University of Tasmania. 

"But we have never been able to locate the volcanic source. This expedition will give us the chance to pinpoint the volcanic belt and to understand how the crust of south eastern Australia was developed", he adds. "To do this, we need to have a detailed understanding of the modern crust forming processes in our region.

"We know that the crust of eastern Australian formed, between 600 and 300 million years ago, and was much like today's South West Pacific region - with chains of island arcs, micro-continental ribbons and intervening small ocean basins", says Professor Crawford.

"By understanding how crust is built in today's setting, we can try to unravel the jigsaw of rocks making up eastern Australia. This will also help us locate ore deposits".

"Rocks will be sampled from about 40 sites on the ocean floor along the submarine scarps and hills on the Norfolk Ridge and adjacent areas, to locate the missing volcanoes and reveal what other groups of rocks are there", says Dr Neville Exon, from Geoscience Australia.  

"Defining the nature of the seafloor in this region will help support Australia's management of its ocean territory and our claims for seafloor jurisdiction beyond the 200 mile Exclusive Economic Zone", says Dr Exon.

The Southern Surveyor, following recent modifications, is able to undertake oceanographic research activities. The research vessel's capacities include fisheries and environmental research, geoscientific research activities and multi-disciplinary marine research. Further modifications, including adding swath-mapping technology, will increase its potential as a National Facility.
For images go to: http://www.ga.gov.au/media/images/ or call the media hotline.

"Maiden Voyage to Find Lost Volcano" Background Information

About 100million years ago, old Pacific Ocean crust was being over-ridden by continental crust along the eastern margin of Australia. Much like the modern Pacific Ocean crust diving westward into the upper mantle beneath Japan. This process of 'recycling' of ocean crust back into the mantle, know as subduction, produces linear chains of explosive volcanoes on the over-riding plate, known as island arcs: Japan is a typical island arc.

For reasons presently poorly understood the hinge line between the over-riding island arc plate and the underthrust Pacific Ocean plate rapidly retreats oceanward - a process known as 'hinge rollback'. Similar to placing towel on the surface of a swimming pool - as one end of the towel gets wet, and thus denser, it commences to sink under its own weight, and as more towel sinks into the pool, the hinge-line at the towel - air - water interface retreats along the towel.

As roll-back happens, it leads to slices of the over-riding plate being calved off and shunted oceanward.  Thus Japan was calved off eastern China 20-15 million years ago.  This same thing happened along the eastern margin of the Australian plate 100-50 million years ago.

Opening of the Coral Sea - Tasman Sea, and the parallel but much narrower New Caledonia Basin, sliced off the massive Lord Howe Rise and ribbon-like Norfolk Ridge from eastern Australia.  Apart from a few tiny islands (Lord Howe Island on the Lord Howe Rise, Norfolk Island on the Norfolk Ridge), these calved off blocks of eastern Australia are now submerged beneath 500-2000m of SW Pacific Ocean.

The subduction implied by the rollback and calving off of the Lord Howe Rise/Norfolk Ridge strongly supported by global plate movement modelling using remote-sensing (mainly satellite-obtained) data, should be manifest in distinctive 100-80 million year old island arc volcanics, such as the rocks that make up much of Japan.

 Yet in eastern Australia, there are remarkably few appropriate rocks recording this important stage of the tectonic evolution of Australia.  

The best candidates are the large pile (> 1 km thick) of volcanic-derived sediments of appropriate age in the Otway - Gippsland - Bass Basins between Tasmania and Victoria.  

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Leharne Fountain
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Geoscience Australia
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Email:	Leharne.Fountain at ga.gov.au

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