Computer Science
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.7806q&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 75, Issue 24, p. 7806-7828.
Computer Science
1
Scientific paper
Acid leaching of the primitive C-chondrite Murchison and O-chondrite QUE 97008 reveal nucleosynthetic anomalies in Cr, Sr, Ba, Nd, Sm and Hf. The anomalies in all but Cr and Sm are best explained by variable additions of pure s-process nuclides to a background nebular composition slightly enriched in r-process isotopes compared to average Solar System material. Leaching leaves a residue in Murchison that is strongly enriched in s-process nuclides with depletions of over 0.1% in 135Ba and seven parts in 10,000 in 84Sr. If there are p-process anomalies in these two elements, they are lost in the variability caused by different r-, s-process contributions to the normalizing isotopes. The concentration and isotope systematics are consistent with the Ba and Sr isotopic composition in the Murchison residue being strongly influenced by s-process-rich presolar SiC. In general, the nucleosynthetic isotope anomalies are 2- to 5-fold smaller in QUE 97008 than in Murchison. The different magnitudes of isotope anomalies are similar to the difference in matrix abundance between CM and O chondrites consistent with the suggestion that the carriers of nucleosynthetically anomalous material preferentially reside in the matrix and that some of this material has been distributed throughout the O-chondrite minerals as a result of thermal metamorphism.Neodymium, Sm and Hf display variable s-, r-process nuclide abundances as in Ba and Sr, but the anomalies are much smaller (e.g. &z.epsiv;148Nd, &z.epsiv;148Sm = -5.7, 2.1, respectively, in Murchison and -0.43, 0.16, respectively in QUE 97008 residues). After correcting Nd and Sm for s-, r-process variability, Sm in whole rock chondrites shows variable relative abundances of the p-process isotope 144Sm that correlate weakly with 142Nd suggesting that the direct p-process contribution to 142Nd is small (˜7-9%). Nucleosynthetic variability in Nd explains the range in 142Nd/144Nd seen between C and O, E-chondrites, but not the difference between chondrites and all modern Earth rocks, leaving decay of 146Sm and a superchondritic Sm/Nd ratio as the likely explanation for Earth's high 142Nd/144Nd.
Carlson Richard W.
O'D. Alexander Conel M.
Qin Liping
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