From: University of New Mexico
Posted: Wednesday, December 29, 2004
Researchers at the University of New Mexico have identified a 2.9 billion year-old lunar meteorite. The meteorite, found in Africa in 2000, was examined by a group of scientists in the Earth and Planetary Sciences department headed by Senior Research Scientist Lars Borg.
Photo: UNM's sample, obtained from the Natural History Museum in London, was named Northwest Africa 773 (NWA 773) describing the location where it was found.
The research titled, "Prolonged KREEP magmatism on the Moon indicated by the youngest dated lunar rock," was featured in Nature magazine recently.
"We use geochronology to date lunar and Martian meteorites," said Borg. "The sample looked interesting as soon as we started working on it." Borg noted the project was group effort in the lab including Yemane Asmerom, Charles Shearer and James Papike.
NWA 773 is a 633-gram lunar meteorite composed of impact breccia containing an olivine-rich clast. The bulk of the clast sample was composed of olivine (48 percent) interpreted to be of igneous origin.
"It was a little piece of rock containing various minerals," said Borg. "It’s not much different than what’s on earth."
The last stage of crystallization of an ocean of lunar molten rock produced materials strongly enriched in incompatible elements and phosphorus and termed KREEP. The materials are typical of the moon’s western hemisphere with the geochemical identity. The decay in radioactive elements, most notably uranium and thorium, are thought to provide the thermal energy necessary for more recent lunar magmatism or what provided heat to melt the lunar rock.
A large amount of the naturally occurring radioactive isotopes samarium and neodymium, described as a parent/daughter relationship by Borg, enabled the team to date the meteorite.
Borg and the research team washed, sonicated and crushed part of the sample to help remove impurities and contaminants from the African desert.
"It allowed us to separate all other ‘junk’ found in the rock," said Borg. "We used ion chromatography to separate out elements of interest."
Based on a series of analytical procedures including the isotopic analyses, the age of NWA 773 was confirmed to be the youngest crystallization age from any previously dated lunar sample – by approximately 250 million years. The findings suggest that the KREEP source may be significantly more evolved than previous estimates suggested.
"At UNM we have a state-of-the-art laboratory to perform these types of studies. There is only one other lab in the world that can do the analyses at this level – NASA," said Borg.
The research is funded through the NASA Cosmochemistry program.
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