[meteorite-list] Lavas from Hawaiian Volcano Contain Fingerprint of Planetary Formation

[Ron Baalke]

News Office
University of Chicago
Chicago, Illinois

MEDIA CONTACT:
Steve Koppes, 773-702-8366

June 19, 2008

Lavas from Hawaiian volcano contain fingerprint of planetary formation

Hikers visiting the Kilauea Iki crater in Hawaii today walk along a mostly
flat surface of sparsely vegetated basalt. It looks like parking lot
asphalt, but in November and December 1959, it emitted the orange glow of
newly erupted lava.

Now, a precision analysis of lava samples taken from the crater is giving
scientists a new tool for reconstructing planetary origins. The results of
the analysis, by the University of Chicago's Nicolas Dauphas and his
associates, will be published in the June 20 issue of the journal Science.

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
and co-authors Fang-Zhen Teng of the University of Arkansas and Rosalind T.
Helz of the U.S. Geological Survey.

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, Dauphas
said.

As the lava in Kilauea Iki crater cooled and solidified, the content of its
iron isotopes evolved with time. "A good analogy is putting a bucket of
salty water in your freezer and monitoring what happens to the salt
concentration in the water as the ice forms," Dauphas said.

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

The June 20 Science article is the first publication based on data collected
and analyzed with the help of a new instrument in Dauphas's Origins
Laboratory. 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).

Isotopic studies have a long history at the University of Chicago. Harold
Urey, who received the 1934 Nobel Prize in chemistry, established the
principles governing isotopic variations as a faculty member at Chicago in
the 1940s and 1950s, Dauphas said.

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," Dauphas said. "We can now
use iron isotopes as fingerprints of magma formation and differentiation,
which played a role in the formation of continents."