Superplume splitting Africa

Rift could be replaced by ocean in 50 million years

 
By Moushumi Sharma
Last Updated: Saturday 04 July 2015

Geophysicist David Hilton hiked to the top of volcanoes in East Africa to collect rock samples to determine whether the rift was caused by a superplume or many smaller plumes

A giant “superplume”—a massive upwelling of molten rock carrying heat from near the Earth’s core up to the crust—is causing a geological rift in Africa that could split the continent into two, says a new study  by the Scripps Institution of Oceanography and the University of California at San Diego. Scientists believe that the rift, running along the eastern side of the continent, will be replaced with an ocean in 50 million years.

According to a report by Scientific American, the separation of Africa’s tectonic plates has been in place for decades. But scientists could not precisely figure out why two massive land masses were moving apart by a few millimetres every year. Geophysicists said two large plateaus—one in Kenya and one in Ethiopia—were created when a superplume pushed up the mantle. This was contradicted by geochemists, who believed there were two small, unrelated plumes pushing up the plateaus individually.

David Hilton, a geochemist at Scripps, set out with his team of researchers to find the truth. They undertook two expeditions in 2006 and 2011 to East Africa and hiked to the top of volcanoes in both sides of the Great Rift Valley: the Kenya Dome and the Ethiopia Dome. One such volcano was Oldoinyo Inyo Lengai, which was a six-hour climb. “We have dinner and then a nap, then start climbing around midnight so we can summit the volcano at dawn. Then we have a whole day to work. This avoids climbing in the peak equatorial heat of the early afternoon,” Hilton told Scripps News. He added that the return is even more exciting. “Sometimes you can almost ski downhill on your boots if there is enough scoria (tiny volcanic pebbles).”

Helium, neon provide answers

Once they reached the peak, the team collected rock samples deposited during eruptions. These were then examined for the presence of helium-3, an isotope of helium that was trapped in the Earth’s core when the planet was forming. According to Hilton, if the rocks around the Kenya Dome and the Ethiopia Dome contained the primordial gas, it would confirm that underground mantle plumes created them. The readings showed the presence of helium-3 in both the plateaus.

This, however, did not answer whether the rift was caused by one giant plume or several lesser plumes? For this, the scientists examined the rocks for neon-22, another primordial gas trapped in the mantle. Scientific American reports that the gas was found in both the plateaus and the ratio of helium to neon in both the sets of rock samples matched, indicating that the two plateaus and the rift were caused by one massive plume of magma. This proves that the geophysicists were right about a superplume all along.

“The ‘naysayers’ who claim that the rifting and plume activity are unconnected—and some who would even deny a mantle plume is present—no longer have a leg to stand on,” Pete Burnard, a geochemist who was not involved in the latest work, told Scientific American.

The African superplume will provide scientists with easier access to study the Earth’s inner workings, the report says. Hilton and his team are now measuring the age of the mantle in East Africa and how much carbon it releases. This information, Hilton says, will help geologists figure out how the Earth’s layers interact on a longer time scale and split.
 

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