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Blank area of ocean floor gets a good going over - 17/03/1999

French and New Zealand scientists are to spend the next 10 days studying an area of ocean floor off Northland which they describe as one of the least understood parts of the south west Pacific.

The Northland Plateau, east of Northland, is an area of about 30,000km2 which features a large plateau and a chain of extinct volcanoes, or seamounts.

" What stands out about the Northland Plateau is that it’s about 300km north of Auckland and nobody knows what it’s made of or how it got there,’’ said project leader Rick Herzer, from the Institute of Geological & Nuclear Sciences Limited.

Information on the area is sparse. It consists of navy depth charts and satellite images, which provide only limited information about the geology of the area.

Dr Herzer said unravelling the geology of this key area would give scientists a better understanding the tectonic evolution of the south west Pacific seafloor as well as the evolution of the North Island.

Scientists believe the area could be one of New Zealand’s most geologically complex offshore areas. They suspect it was a former tectonic plate boundary that has been compressed, stretched, penetrated from below by lava, and shunted in many directions – including over parts of onshore Northland - over millions of years.

Establishing the order of these events, and how long each phase lasted is one of the expedition’s goals.
" There are several theories about the evolution of this area, but until we inspect it closely we won’t know which one is right. It could be that none of them is quite right’’

Finding out the age and composition of the rocks on the ocean floor and working out how they got there, will give geologists a better framework to determine northern New Zealand’s mineral and hydrocarbon potential.

" Estimates for the age of the rocks in this area range between 10 and 100 million years. The age, composition, and tectonic history of New Zealand’s other offshore areas is better established. The Northland Plateau is a blank page.’’

In-depth knowledge of the seafloor is a crucial to New Zealand’s bid to the United Nations Law of the Sea Convention (UNCLOS). New Zealand has until 2006 to lodge a claim to potentially almost double the area covered by its Exclusive Economic Zone. The New Zealand EEZ is currently the fourth largest in the world.

Claims lodged by Australia and the Pacific islands will overlap New Zealand’s claims in several areas, including the Three Kings Ridge which is attached to the Northland Plateau.

The study will be done from the research ship Tangaroa with scientists using seismic reflection equipment and dredging to help fill the information gaps.

Seismic reflection, widely used in the oil exploration industry, enables scientists to image rocks up to several kilometres below the seafloor. It reveals not only the type of structures, but their relative ages.

A number of peaks and other seafloor structures have been targeted for dredging which involves dragging a steel trawl along the seafloor where instruments indicate rock outcrop. Up to 50kg of rock and sediment is hauled up with each dredge. Samples will be analysed in Wellington and at several overseas research institutes.

Dr Herzer described the Northland Plateau as the last piece of the Pacific tectonic jigsaw puzzle. It had been left behind as scientists focused on hydrocarbon-bearing areas and the active plate boundary around New Zealand, or regions further to the north in the south Pacific.

" Understanding what has happened in the Northland Plateau is likely to affect our geological understanding of the New Caledonia and Fiji regions.’’

In 1993 GNS worked with French and Australian scientists to study the southern Norfolk Ridge/Three Kings Ridge area. Results from that study improved the understanding of the geology and offshore mineral resources of the area between the northern tip of New Zealand and Fiji.

Knowledge gained from the 1993 study had benefited all three countries, especially New Zealand. The study uncovered a huge new deep-water region with petroleum potential between Northland and Norfolk Island, Dr Herzer said.

  • Participating with GNS in the Northland Plateau expedition are scientists from Geosciences Azur and the French University of the Pacific in New Caledonia. Geosciences Azur is a consortium of French universities and government research organisations based in Nice that undertakes international geological studies.
  • The Northland Plateau expedition is one of several collaborative projects involving GNS and Geosciences Azur, with the French Government contributing financially to the research.
  • The expedition leaves Auckland on March 19 and returns to Auckland on March 29.

Contact:Dr Rick Herzer