11
November 2004
KREEP factor
NWA 773 (Northwest Africa 773) is a lunar meteorite found in September 2000 in the Western Sahara. New dating experiments using the Sm–Nd isotope clock confirm previous reports that this is the youngest volcanic lunar rock known, with a crystallization age of about 2.9 billion years. The new dating extends the chronology of a type of lunar magmas referred to as KREEP-rich lavas by about 1 billion years. KREEP stands for potassium (K), rare earth elements (REE) and phosphorus (P). Decay of radioactive elements in KREEP is thought to have provided the energy necessary for more recent lunar volcanism.
Prolonged KREEP magmatism on the Moon indicated
by the youngest dated lunar igneous rock
LARS E. BORG, CHARLES K. SHEARER, YEMANE ASMEROM &
JAMES J. PAPIKE
Nature 432, 209–211 (2004); doi:10.1038/nature03070
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