Ocean study gives new quake, minerals insight

By Tom McNiff

WOODS HOLE, Massachusetts (Reuter): A pioneering joint American-Japanese deep sea oceanographic project is providing new insight into areas of the earth's crust as well as clues to how earthquakes occur and mineral deposits are formed.

Scientists at the Woods Hole Oceanographic Institution (WHOI) and the Japan Marine Science & Technology Centre (JAMSTEC) said this week their work in the Atlantic Ocean is providing a start to understanding the earth's internal workings as they probe the ocean crust and the mantle -- a layer between the crust and the earth's core.

"The important point ... is to understand the information coming up from the interior of the earth to the sea floor...," Hiroshi Hotta, JAMSTEC's deep-sea research director, told Reuters during a recent briefing on the project.

This year's project is the first U.S.-Japanese joint deep sea diving effort although the two institutions have cooperated since 1973 on other research matters.

The Japanese submersible craft Shinkai 6500 set a new dive record as scientists guided the vessel to the bottom of a 20,000- foot (6,000-meter) deep undersea fissure from which they got views of active geophysical forces similar to those that formed the undersea crust, which covers about 70 percent of the earth's surface.

While the scientists are using an array of advanced technology the picture that is emerging is far from clear.

"Actually it is not a good window into the crust," William Bryan, a WHOI geologist who worked with Japanese scientists on Shinkai 6500, said last Wednesday of the deep fissure. "It's like a window with the shades drawn."

Measurement

The pit lies in a part of the seismically and volcanically active Mid-Atlantic Ridge known as the Kane Fracture Zone, where earthquakes collapse the ocean crust to great depths and push it into high mountains a few miles away, often nearly simultaneously.

Using high-tech instruments and direct observation, the Shinkai 6500's three occupants measured gravity and magnetic fields inside the fissure and gathered samples of mantle rocks deformed by the same fierce forces that disturb oceanic plates to create sub-sea earthquakes.

On one of 15 dives made into the Kane area, the scientists found that earthquakes along a fault line ground up and collapsed huge rocks and created rockslides similar to those in earthquake- prone areas on land.

One of the questions still unanswered is whether the Kane site hosts hydrothermal vents similar to those studied by WHOI scientists in a parallel expedition this summer.

The Shinkai 6500 will dive to that area in August to place instruments that will measure the effects of drilling into an ocean bottom mound whose top is festooned with chimney-like formations that spew forth black "smoke" -- gasses formed when cool seawater mixes with hot minerals within the ocean crust and possibly deeper.

"Some of the gasses are probably coming from the mantle -- it's probably the first time they're out on the earth's surface," said Susan Humprhis a geochemist at the Woods Hole Institute.

A drilling ship will try to probe the mound to retract core samples that may be useful in pinpointing mineral deposits on land as well as clues to how the sea's interaction with the earth's interior heat influences climate.