ABSTRACT

We have measured high-precision W isotope ratios for series of carbonaceous and ordinary chondrites. The resulting ¹⁸⁴W/¹⁸³W ratios for three carbonaceous chondrites (Murchison CM2, Y-793321 CM2, and Y-86751 CV3) did not vary significantly from that of the W isotopic standard (NIST SRM 3163) and various terrestrial rocks, whereas the ¹⁸⁴W/¹⁸³W ratios for Allende CV3 showed ∼0.4ε lower value than the other chondrites and terrestrial samples. This deficiency in the measured ¹⁸⁴W/¹⁸³W ratio for the Allende CV3 could not be attributed to the incomplete digestion of acid-resistive presolar components such as SiC grains with abundant s-process nuclides, because the SiC contents in the Allende was significantly lower than those for other carbonaceous chondrites. Several possible explanations for the deficiency in the ¹⁸⁴W found in the Allende CV3 were explored. We conclude the results could be best explained by the isotopic heterogeneity of W by contribution of r-process enriched components to the source material of the Allende CAIs. The finding is consistent with the recent observation of some CAIs in Allende was enriched in the r-process nuclide of W (Burkhardt et al., 2008) and supported by the fact that the CAI contents in the Allende chondrite are significantly higher than that in other carbonaceous chondrites.