Scientists to drill into Zealandia, the lost continent beneath New Zealand

Thursday, 20 July 2017

A $120 million drilling programme into the sea floor around New Zealand will reveal the massive natural forces at work, and help explain how the mostly underwater continent of Zealandia formed.

Scientists from around the world are to join their New Zealand colleagues on six voyages during the next 18 months on 143-metre long international research ship Joides Resolution. Its drill can get to depths of 8235m below the ocean surface.

The research is being funded by the 23-nation International Ocean Discovery programme, which operates the ship.

Core samples taken from six sites in the Tasman Sea during the next couple of months are expected to answer many questions about the mostly submerged continent of Zealandia.

The first voyage, which starts next week and takes two months, will drill six holes into the ocean floor under the Tasman Sea to learn about how one tectonic plate starts being subducted under another.

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International research drilling ship Joides Resolution, which will be making six voyages into the seas around New Zealand in the next 18 months.

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'This expedition will answer a lot of lingering questions about Zealandia,' expedition co-chief scientist Gerald Dickens, professor of Earth, environmental and planetary science at Rice University, said.

Drilling will be done at depths ranging from 1000-5000m, with cores being collected from 300-800m into the sea floor. The cores will contain samples iof sediments deposited over millions of years, and will include fossils that can be used to assemble a detailed record of Zealandia's past.

The expedition – number 371 – will examine a shift that happened about 50 million years ago in the direction of movement of the enormous Pacific Plate northeast of Zealandia. The expedition refers to this shift as 'the most profound subduction initiation event and global plate-motion change' in the past 80m years.

Before it happened, Australia and New Zealand were spreading apart, and after the shift, the area that separated them was under compression for millions of years. Then, in the final stage of the tectonic shift, the Pacific Plate slipped beneath Zealandia, forming a new subduction zone. This relieved the compressive forces across the region.

The research could also answer many questions about the way Earth's climate evolved in the past 60m years, Dickens said. The findings could reveal how ocean currents changed at the time.

Jamie Allan, programme director of the US National Science Foundation's Division of Ocean Sciences, said the diving of the Pacific Plate under New Zealand resulted in the uplift of New Zealand above the waterline and the development of a new arc of volcanoes.

Zealandia is a mass of continental crust – the layer of rocks that form the continents and areas of shallow seabed close to their shores, and which is less dense than oceanic crust. It surrounds New Zealand and more than 90 per cent of it is submerged. About 100m years ago, Antarctica, Australia and Zealandia were all one continent. Zealandia split off about 85m years ago.

GNS Science said other expeditions in the research programme included voyages to:

- Target slow-slip earthquakes and submarine landslides off the coast of Gisborne

- Investigate seafloor hydrothermal systems at Brothers volcano northeast ot Bay of Plenty, where highly acidic fluids at more than 300 degrees Celsius are belching into the ocean

- Probe the seafloor off the Ross Ice Shelf to improve understanding of the stability of the West Antarctic Ice Sheet through cycles of warming and cooling during the past 20 million years