Ocean geologists hatch plan to probe ancient zone

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US and Japanese geologists are planning a major investigation of the Izu-Bonin-Mariana Arc, a 2,800-kilometre subduction zone located in the Pacific Ocean south of Japan. Studying the region, where one oceanic plate is sliding underneath another, could shed light on many geological process, including how the first continents formed. “This collaboration will be one of the most concentrated geoscientific efforts over the next ten years,” says Jim Gill, a geologist at the University of California, Santa Cruz.

Japanese researchers will have racked up seven one-month research missions to the area by the end of the year, and the US National Science Foundation (NSF) has invested $4.5 million in studies there over the past few years. At a meeting held in Hawaii earlier this month by the NSF and Japan's Institute for Frontier Research on Earth Evolution, researchers outlined their plans for the coming decade.

Studies of the arc have been prioritized by the NSF and various Japanese research institutes, partly because the crust over oceanic plates is thinner than the continental crust, making it easier to obtain information from seismological signals. The relatively old age of the plate, which has been undergoing subduction for 43 million years, is a further incentive. Some researchers believe that the first continents were created in similar oceanic subduction zones. “It is the closest thing to how our continents got started some 3–4 billion years ago,” says Gill.

At the Hawaii meeting, experiments to conducted with Chikyu, a new ocean-drilling ship that is due to enter operation in 2006 (see Nature 415, 356; 2002), were cited as central to future studies. Geologists want to use the vessel's 7-kilometre drilling capacity to sample directly the composition of the crust and underlying mantle.

Time on Chikyu will be in short supply, however, as other groups are competing for time on the vessel. A single drilling mission takes around a year, so trips will be limited. A smaller collaboration is also bidding to use Chikyu to explore a subduction zone under the Aleutian Islands off the coast of Alaska.

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Cyranoski, D. Ocean geologists hatch plan to probe ancient zone. Nature 419, 328 (2002) doi:10.1038/419328b

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