DIFFERENTIATED ACHONDRITES ASUKA-881371, AN ANGRITE, AND DIVNOE - NOBLE-GASES, AGES, CHEMICAL-COMPOSITION, AND RELATION TO OTHER METEORITES

We present a study of the noble gas isotopic abundances in two achondr ites, Divnoe and the Asuka 881371 angrite. For Divnoe, we also perform ed chemical analyses of the major elements and of some minor and trace elements that are relevant for the comparison with other meteorite ty pes and for the interpretation of the noble gas data. Based on the cos mic-ray produced noble gases, an exposure age of 5.4 +/- 0.7 Ma for As uka 881371 was obtained. This ejection time from the parent asteroid d iffers from those of the other three angrites-Angra dos Reis (55.5 Ma) , LEW 86010 (17.6 Ma), and LEW 87051 (greater than or equal to 0.2 Ma) . Whereas the U,Th-He-4, and K-Ar-40 gas retention ages of Asuka 88137 1 are 3750 +/- 1000 Ma and 3910 +/- 500 Ma, respectively, we derive fo r the Pu-244-Xe-136 system, a formation age of 4533 +/- 40 Ma, which i s contemporaneous with that of the other angrites Angra dos Reis and L EW 86010. For Divnoe the abundance patterns of the major lithophile, s iderophile, refractory, and volatile elements, the isotopic abundance pattern for primordial trapped Xe, and the oxygen isotopes indicate th at this unique meteorite is related to the brachinite achondrites. Ass uming no pre-exposure to cosmic rays on the parent body, Divnoe's aste roid ejection event occurred 17.2 +/- 2.3 Ma ago. Copyright (C) 1997 E lsevier Science Ltd