A new 1.3 Aeon-Young achondrite

The Ar-40/Ar-39 age of Governador Valadares, a Nakhlite achondrite, has been determined to be 1.32 plus or minus 0.04 billion yrs. The K-Ar age and cosmic-ray exposure age of Governador Valadares are essentially identical to analogous ages for the two other known Nakhlite achondrites and to Rb-Sr ages determined for Nakhla. These data suggest that all three known meteorites of this class were derived from the same parent body by a common event, and confirm that Governador Valadares is a member of this class. The most probable heat source for producing such meteorites may be collisional melting of a portion of the parent body. Nakhlites may represent a rare phenomenon and may not be at all representative of the surface of their parent body.