Discovery of non-radiogenic tungsten isotopic anomalies in the Allende CV3 chondrite

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. (author)