Oregon State University

Hard-Rock Story

Anthony Koppers and team

Talk about taking things in stride. Three scientists stand at a ship’s railing, arms on each others’ shoulders, sun on their faces and a calm blue sea behind them. They look like tourists on a cruise. Nothing in their calm expressions suggests that they have just pulled half a mile of rock out of the Earth. Or that the rock will help them to answer questions about  how the planet’s tectonic plates move or about how microbes mingle with heat, water and pressure deep underground.

Oregon State University Professor Anthony Koppers and Toshitsugu Yamazaki of the Geological Society of Japan were co-leaders of the latest cruise conducted under the auspices of the International Ocean Drilling Program (IODP). Their target:  the Louisville Seamount Trail — a 2,600-mile-long line of underwater mountains in the South Pacific — where they hoped to learn more about the geophysical processes that produce such features as the Hawaiian Islands or the stretch of ancient volcanoes between the Oregon Cascades and Yellowstone National Park.

Koppers co-edited a special March 2010 issue of the journal Oceanography focusing on seamount science.

According to an IODP news release, the scientific team on the research vessel, JOIDES Resolution, returned to Auckland, New Zealand on February 15 with 806 meters of rock pulled from the seamounts. “During this expedition, we sampled many ancient individual lava flows and a fossilized algal reef.  These samples will be used to study the construction and evolution of the individual Louisville volcanoes,” said Koppers.

Added Yamazaki: “The sample recovery during this expedition was truly exceptional. I believe we broke the recoveryJOIDES Resolution record for drilling igneous rock with a rotary core barrel.” A rotary core barrel is a type of drilling tool used for penetrating hard rocks.

The samples were recovered from six sites at five seamounts varying in age from 50 to 80 million years old.

Linear trails of volcanoes found in the middle of tectonic plates, such as the Hawaii-Emperor and Louisville Seamount Trails, are believed to form from a hotspot – a plume of hot material found deep within the Earth that supplies a steady stream of heated rock from depths as great as 2,900 km up to the surface. As the tectonic plate drifts over the hotspot, new volcanoes are formed – and old ones become extinct. Over time, a linear trail of these aging volcanoes is formed.

“Submarine volcanic trails like the Louisville Seamount Trail are unique because they record the direction and speed at which tectonic plates move,” explained Koppers.

Scientists use these volcanoes to study the motion of tectonic plates, comparing the ages of the volcanoes against their location over time to calculate the rate at which the plate moved over a hotspot. These calculations assume the hotspot stays in the same place over time.

core of recovered volcanic rock“The challenge,” said Koppers, “is that no one knows if hotspots are truly stationary – or if they somehow wander over time. If they wander, then our calculations of plate direction and speed need to be re-evaluated.”

“But even more importantly,” he continued, “the results of this expedition will give us a more accurate picture of the dynamic nature of the interior of the Earth on a planetary scale.”

Recent studies in Hawaii have shown that the Hawaii hotspot may have moved as much as 15° latitude (about 1,600 kilometers or 1,000 miles) over a period of 30 million years.

“We want to know if the Louisville hotspot moved at the same time and in the same direction as the Hawaiian hotspot – our models suggest that it’s the opposite, but we won’t really know until we analyze the samples from this expedition,” explained Yamazaki.

In addition to the volcanic rock, scientists on this expedition also recovered sedimentary rocks that preserve shells and an ancient algal reef – typical of living conditions in a very shallow marine environment. These ancient materials show that the Louisville seamounts were once an archipelago of volcanic islands.

According to Koppers, “we were really surprised to find only a thin layer of sediments on the tops of the seamounts and only very few indications for the eruption of lava flows above sea level. It seems that the volcanoes have only been at or above the surface of the ocean for a short amount of time – we weren’t expecting this.”

Read more on this story at Terra Magazine

Photos (from top) courtesy of IODP-USIO, D. Buschs (Australian National University), IODP-USIO

Video: With the JOIDES Resolution, Expedition 330 is drilling into Seamounts on the Louisville Seamount Trail in the western South Pacific Ocean to study hotspots

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