CORVALLIS - Researchers from Oregon State University have discovered that some of the sea mounts originating from the volcanic chain of the Hawaiian "hot spot" were significantly influenced by the existence of a mid-ocean ridge that long since has been subducted under present-day Siberia.
The findings, published today (June 8) in the journal Nature, are important because they provide more evidence into the workings of volcanic hot spots that created Hawaii and Iceland, and are still active in oceans throughout the world.
"It's an important new piece of the puzzle for determining how tectonic plates work and how these deep-seated hot spots interact with what's going on at the surface," said Randall Keller, an assistant professor in OSU's College of Oceanic and Atmospheric Sciences and lead author of the article. Martin Fisk of OSU and William White, Cornell University, are co-authors on the study.
The Hawaiian hot spot is the largest and one of the oldest hot spots in the world, responsible not only for creating the Hawaiian Islands, but also a string of underwater sea mounts that stretch across the Pacific Ocean toward the east Asian coast line.
A hot spot is a place in the ocean where magma is brought up from deep within the Earth. When it reaches the surface, it cools, creating volcanic rock formations. As the tectonic plates shift over millions of years, these formations move away from the hot spot and another forms in their place.
"It's like a gigantic volcano conveyer belt," Keller said.
The research team studied one of the oldest of these formations, thought to be about 80 million years old. After drilling through 900 meters of sediment they reached rock and drilled another 87 meters to retrieve samples. Through sophisticated chemical analysis they discovered a chemical "signature" that matched rocks from mid-ocean ridges such as the Juan de Fuca ridge, but was unlike anything known from Hawaii.
What surprised the researchers was that the composition of the rock indicated that it came from magma that had melted relatively close to the surface. The composition of the rocks was characterized by low levels of potassium, strontium and rubidium, which are easily removed from a rock when it is melted near the surface. Rock melted far below the surface is more "pristine," Keller said, with higher levels of those elements present.
Many scientists theorize that hot spots are like giant tubes that extend far into the Earth, in part because they were thought to be stationary. However, there is some evidence that suggests that these hot spots actually migrate, a theory that will be tested when another research team, including OSU scientists, plans to explore the northernmost sea mount in the Hawaiian chain in the summer of 2001. The last cruise, aboard the research ship JOIDES Resolution, looked at the next-to-last sea mount, which turned out to be 80 million years old.
"Logic suggests that the last sea mount will be older, because the chain moves in that direction," Keller said. "What no one knows, however, is whether that is the oldest volcano, or there were others in that chain that already have been subducted."
The researchers hope to conduct a series of paleomagnetic studies that will determine at what latitudes the volcanic eruptions occurred that created the sea mount. Such findings would help determine whether the hot spot has moved.
Existence of a mid-ocean ridge on top of the Hawaiian hot spot isn't surprising on one hand, Keller said, because there are parallels existing today in Iceland and at the Axial sea mount on the Juan de Fuca ridge. However, the Hawaiian hot spot has been studied for years and no one could confirm the ridge's previous existence.
"We have seen in other places around the world how ridges can influence a hot spot," Keller said, "but it's interesting that it took place in Hawaii, which is the largest hot spot on Earth. Despite its vast size, it was still highly susceptible to what was going on at the surface."
By Mark Floyd, 541-737-0788
Journal
Nature