Scientists get a new tool for reconstructing planetary origins

Washington, June 20 : A precision analysis of lava samples taken from the Kilauea Iki crater in Hawaii crater is giving scientists a new tool for reconstructing planetary origins, by revealing more about the formation of the crust than previously thought.

The analysis was done by University of Chicago's Nicolas Dauphas and his associates Fang-Zhen Teng of the University of Arkansas and Rosalind T. Helz of the US Geological Survey.

"A close examination of iron isotopes-the slight variations the element displays at the subatomic level-can tell planetary scientists more about the formation of crust than they previously thought," according to Dauphas.

If applied to a variety of terrestrial and extraterrestrial basalts, including meteorites from Mars and the asteroids, the method could provide more definitive evidence for a scientifically popular idea that the moon was born from a giant collision between Earth and another large object, he added.

As the lava in Kilauea Iki crater cooled and solidified, the content of its iron isotopes evolved with time.

The finding contradicts the widely held view that isotopic variations occur only at relatively low temperatures, and only in lighter elements, such as oxygen.

But Dauphas and his associates were able to measure isotopic variations as they occur in magma at temperatures of 1,100 degrees Celsius (2,012 degrees Fahrenheit).

Previous studies of basalt found little or no separation of iron isotopes, but those studies focused on the rock as a whole, rather than its individual minerals.

"We analyzed not only the whole rocks, but the separate minerals," said Teng.

In particular, they analyzed olivine crystals, better known as peridot in the jewelry world.

The instrument, a plasma source mass spectrometer funded by the National Aeronautics and Space Administration and the University of Chicago, separates ions (charged particles) according to their masses.

These ions are formed in a plasma of argon gas within the instrument at a temperature of nearly 14,000 degrees Fahrenheit (8,000 degrees Kelvin, hotter than the sun's surface).

The researchers selected Kilauea Iki for their study because scientists have drilled it for samples multiple times as it cooled over the years. This sequence of samples makes the lava lake a perfect site for studying differentiation-the separation of minerals and elements as magma cools and hardens.

"Our work opens up exciting avenues of research," said Dauphas. "We can now use iron isotopes as fingerprints of magma formation and differentiation, which played a role in the formation of continents," he added.

ANI