MIT researcher finds clues to formation of Indian Ocean

One rock establishes a role for continental crust


CAMBRIDGE, Mass.--A Massachusetts Institute of Technology researcher co-led a team of 25 international scientists in a recent ocean-floor drilling expedition to the Kerguelen Plateau in the southeast Indian Ocean. The researchers discovered clues in this huge sunken island complex that may shed light on exactly how Antarctica, Australia and India broke up into separate land masses around 130 million years ago.

On December 13 at the annual meeting of the American Geophysical Union in San Francisco, Fred Frey, professor of geochemistry at MIT and co-chief scientist on the drilling expedition, will report on the results of several drilling forays up to 200 meters into the plateau's "basement." The researchers retrieved black volcanic rock that holds clues about how the Earth evolved.

The Kerguelen Plateau was formed by one of the most cataclysmic volcanic events in the Earth's history. So much magma spewed forth that it covered a land mass one-third the size of the continental United States with a 20-kilometer-thick layer. "This makes Mount Pinatubo look like a pinhead," Frey said. "The major objective of our drilling program was to retrieve rocks that would enable us to more precisely constrain the eruption ages. Regardless of the exact time of the eruption, production of this much magma clearly is a major geologic event."

An earlier ocean-drilling expedition uncovered evidence that the Kerguelen Plateau was above sea level during its intense volcanic period. Sediments on top of the cooled magma had trapped wood, seeds, spores and other organic matter that indicates that the plateau was high and dry. Frey said that the land mass forming the Kerguelen Plateau existed above sea level for several million years before it cooled, shrunk and sank. Now only a few small islands rise above seal level: the Kerguelen archipelago owned by France and the smaller Heard and McDonald islands, which belong to Australia.

"We found that most of the plateau is formed of basalt, a magma type that erupts relatively 'quietly,' but that near the end of the plateau growth, there is strong evidence of highly explosive eruptions," Frey said. "This is significant because explosive eruptions input more material into the atmosphere and are more likely to have environmental consequences."

Core from one of the drilling holes included a rock that is found only on continents. Almost as soon as the rock was recovered on the deck of the 143-meter scientific research vessel JOIDES Resolution, Frey said, "It was apparent that we had a spectacular and unexpected result. That's not an oceanic rock, yet it was sitting in the middle of the ocean." The core will shed light on the continental drift that led to the formation of the Indian Ocean.

MIT graduate student Kirsten Nicolaysen reported at a recent annual international geochemical meeting that the rock is a continental fragment as much as 900 million years old. "The surprise is that the Indian Ocean is less than 200 million years old," Frey said. "Apparently, when India, Australia and Antarctica broke up to form the Indian Ocean around 130 million years ago, a fragment of these continents was broken off and incorporated into the newly forming Indian Ocean."

The ocean-drilling program is funded by the National Science Foundation with contributions from several participating countries.


Topics: Earth and atmospheric sciences, Oceanography and ocean engineering

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