Probing secrets of earth's plates

By Jamie Morton

Scientists want to learn more about the tectonic surfaces we ride on and what happens at their boundaries.

A high level of interest in the workshop from overseas scientists reflected the importance of New Zealand's geological setting. Photo / File
A high level of interest in the workshop from overseas scientists reflected the importance of New Zealand's geological setting. Photo / File

Scientists from across the world have come here to examine how to unlock secrets hidden within our offshore tectonic plate boundaries over the next decade, potentially resulting in multi-million dollar projects.

Around 160 leading scientists from 10 countries are in Wellington this week for the GeoPrisms workshop, picking projects from a wish-list of earth science research proposals.

The studies centre on activity at the boundaries of the Pacific Plate and the Australian Plate, and the process of "subduction", when one is pulled under another.

Despite the relatively slow movement, this process gives rise to earthquakes, volcanism and other geological phenomena that scientists want to learn more about.

These subduction zones are among the more active in the world and are thought to be capable of producing giant "mega-thrust" earthquakes and tsunamis, as well as being responsible for the long history of volcanic activity in the central North Island and the Kermadec Arc.

Yet little is known about the mechanisms at play.

Among the proposed projects is a multi-million dollar plan to drill into the interface between the Pacific and Australian plates east of Gisborne to obtain direct evidence of the processes occurring at the plate boundary.

This project, subject to rigorous safety checks, would involve inserting instruments in the drill holes to record a range of physical and chemical phenomena.

Other places where such drilling could be considered include the Brothers volcano in the Kermadec Arc, 400km northeast of the Bay of Plenty, and at the Lord Howe Rise about 1500km northwest of Northland, to help understand how and why subduction began beyond northern New Zealand 45 million years ago.

"New Zealand is unique in the world in having a plate boundary that exhibits many different aspects of subduction, including a wide variety of earthquake and volcanic behaviour," said workshop convener Dr Laura Wallace.

"The New Zealand setting represents a superb opportunity for the international earth science community to find answers to the many outstanding questions about why subduction zones behave the way they do."

A high level of interest in the workshop from overseas scientists reflected the importance of New Zealand's geological setting, she said.

As part of its earth science research programme, the National Science Foundation in the US had picked New Zealand as one of three places where a large amount of research effort and money will be spent on understanding subduction plate boundary phenomena over the next decade.

The foundation chose New Zealand largely because of the high level of tectonic research that has already been done here by New Zealand-based scientists, and the outstanding opportunities for establishing productive collaborations between US and New Zealand scientists.

New Zealand's substantial investment in scientific infrastructure, such as the GeoNet monitoring network, also made New Zealand a compelling location for subduction zone research.

Plan to drill into marine volcano

It reads like something out of science fiction: an active underwater volcano, a team of international experts - and a giant drill.

To scientists, the Brothers Volcano represents the world's best opportunity to understand how magmatic hydrothermal systems work within submarine volcanos.

The volcano, 400km northeast of White Island, is perhaps the best mapped and understood submarine volcano known to science.

Three kilometres wide and with a highest peak 1.2km below sea level, Brothers is the most hydrothermally active of all the volcanoes along the Kermadec Arc - itself arguably the most active chain of submarine volcanoes in the world.

It continually throws up dark, metal-rich plumes of dissolved minerals which, when hitting cold seawater, precipitate out and gather on the sea floor.

As this reaction occurs it can also build "chimneys" rich in metals above the vents.

One of two vent fields that sharply contrast in their chemistry is responsible for large mineral deposits of copper and gold.

By drilling into the volcano, scientists hope to unlock the secrets of its magma chamber, test computer models of its sea floor hydro-thermal plumbing, find out about the transport of precious metals inside the volcano, and assess diversity of microbial life within the volcano.

GNS Science research geologist Dr Cornel de Ronde said the main aim was to recover several hundred metres of drill core from inside the volcano for analysis. Instruments would be inserted in the holes.

"The project will improve the understanding of processes such as the transport of metals from magmas to the sea floor," he said.

A pre-proposal was recently submitted to the Integrated Ocean Drilling Programme, a consortium of 25 countries, which would assess the project before deciding whether to call for a full proposal.

If it was approved, it was unlikely the project would kick off before 2016 and it could cost up to $10 million, which would be borne by the panel.

NZ may hold key to silent quake puzzle

For scientists striving to solve the mystery of newly-discovered "silent" earthquakes, the key to the puzzle might be hidden just off the east coast of the North Island.

These quakes, also known as slow-slip quakes, represent movement between tectonic plate boundaries over periods of weeks or months, rather than in a single large thrust.

They have been detected at extremely shallow depths off the coasts of Gisborne and Hawkes Bay at the Hikurangi subduction zone - a plate boundary fault where one plate dives or "subducts" under another.

Large quakes in such subduction zones also pose the threat of tsunami - such a scenario near the coast of New Zealand could swamp coastal populations with less than an hour's notice.

But little is known about silent quakes, which have been documented across the world and usually happen well below the earth's surface - sometimes as far down as 40km.

The Hikurangi zone offered scientists an opportunity to learn more about these quakes as it could be directly accessed with ocean drilling methods, said Dr Laura Wallace of the University of Texas.

- NZ Herald

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