FSU scientist finds evidence of high iron content beneath Hawaii

09/29/04

TALLAHASSEE, Fla.--A new set of measurements has allowed a Florida State University geochemist to confirm what other scientists have only suspected about what lies deep below the Earth's surface.

Professor Munir Humayun has found that there is a higher iron content in the Earth's mantle beneath Hawaii compared to other regions of the mantle. Hotspot islands, such as Hawaii, arise from hot plumes of solid rock from deep within the mantle or the core-mantle boundary that ascend at rates of a few centimeters per year.

While seismologists had long thought that the Earth's deep mantle - the rocky layer between 1,000 to 3,000 kilometers deep - beneath the Hawaiian islands has a higher concentration of iron, no one had ever precisely measured it until now, according to Humayun. Iron is one of the four main components of the mantle.

"This is a major intellectual advance for science," Humayun said. "The fact that scientists can stand on the Earth's surface and tell you what's going on 3,000 kilometers below is a real breakthrough."

Humayun of the National High Magnetic Field Laboratory and geological sciences department at FSU, Liping Qin of the University of Chicago and Marc Norman of Australian National University found that lavas from Hawaii were about 10 percent higher in iron relative to manganese and other elements compared to rocks from other volcanic regions, particularly the volcanic mountains along the mid-oceanic ridges that form the division between the Earth's tectonic plates. Their findings are published in the Oct. 1 issue of the journal Science.

"The 10 percent was the number seismologists were looking for," Humayun said. "They were right, and we are the first to confirm it."

The findings show that iron is higher in the deep mantle, compared with the upper mantle above about 1,000 kilometers. Humayun theorizes that the excess iron was introduced into the mantle by chemical reactions between rock and liquid metal at the boundary between the Earth's core and mantle.

To get the high quality measurements, Humayun, Qin and Norman used a magnetic sector mass spectrometer instrument to compare the ratio of iron to manganese, a related element that behaves similarly to iron, in lava samples from Hawaii. Their findings are significant because of the possibility that earth scientists may be able to use this method to find out more about the iron-rich core, below the mantle.

"This is of enormous interest to scientists studying the Earth's deep interior," Humayun said.

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