NOBLE-GASES AND STRONTIUM ISOTOPES IN THE UNIQUE METEORITE DIVNOE

We present an isotope study of noble gases in Divnoe, an anomalous met eorite, and also Rb-Sr and K-Ar dating of this meteorite. The relative ly young Rb-Sr age obtained (3.39 Ga) seems doubtful and, most probabl y, results from weathering or contamination. The ancient K-Ar age (4.6 7(-0.40)(+0.20)), together with clear excess of Xe-129, allows the sug gestion of very early formation of the Divnoe meteorite. Concentration s and isotope ratios of noble gases in Divnoe are: 17.9 less than or e qual to He-3 less than or equal to 29.0 x 10(-8); Ne-20 = 6.22 x 10(-8 ); 2.44 less than or equal to Ar-36 less than or equal to 5.10 x 10(-8 ); Xe-130 = 41.3 x 10(-12) cm(3)/g; 0.079 less than or equal to He-3/H e-4 less than or equal to 0.193; Ne-20/Ne-22 = 0.860; Ne-21/Ne-22 = 0. 927; 3.47 less than or equal to Ar-40/Ar-36 less than or equal to 9.47 ; 2.22 less than or equal to Ar-36/Ar-38 less than or equal to 3.27; X e-129/Xe-132 = 1.09. The exposure age calculated from cosmogenic He-3, Ne-21, and Ar-38 is 17.9 +/- 0.9 Ma. On the basis of the isotope data for the noble gases and O, and abundances of K, Rb, and Sr, an attemp t was made to estimate the relationship of Divnoe to other meteorite t ypes. The O-isotope characteristics of Divnoe are clearly distinct fro m those of ordinary chondrites, acapulcoites/lodranites, and SNC meteo rites (Petaev ef al., 1994, Clayton, 1993). In plots of Xe-136 vs. Xe- 129/Xe-130, the Divnoe data fall outside of the data fields for carbon aceous and enstatite chondrites. The light noble gas data, especially the Ar-40/Ar-38 ratio, and the Ar-40, Ar-38, He-3, and He-4 contents o f Divnoe differ significantly from those of all meteorite types except diogenites. The K, Rb, and Sr abundances in Divnoe are substantially lower than in most other meteorites. In the concentrations of these el ements, as well as in the REE pattern, the Divnoe meteorite is similar only to diogenites. Divnoe probably should be treated as a restite re maining after partial melting of the chondritic mantle of a parent ast eroid body.