Sm-Nd systematics of zircon

¹⁴⁷Sm-¹⁴³Nd and ¹⁴⁶ Sm- ¹⁴²Nd systems were studied in nineteen 3.32-4.02 Ga zircon grains from Jack Hills metaconglomerate, 12 of which were previously analyzed for Lu-Hf. Nd concentrations in the zircons are 0.9-20 ppm. The amount of Nd recovered was between 13 and 446 pg. The analytical precision of ¹⁴²Nd/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios varied between 0.004% and 0.08% (2σm) depending on the sample size. The ¹⁴⁷Sm/¹⁴⁴Nd ratios vary from 0.4 to 1.2. ¹⁴³Nd/¹⁴⁴Nd ratios are variably radiogenic, from 0.5125 to 0.5346. Combined interpretation of ¹⁴⁷Sm- ¹⁴³Nd and U-Pb systems shows that LREE in zircons are a mixture of a primary component with high Sm/Nd (>1.6-2.0), and a secondary, younger component with low Sm/Nd. Determination of initial ε¹⁴³Nd of ancient zircons with a precision and accuracy sufficient for petrogenetic interpretations may not be possible because of large errors in the ¹⁴⁷Sm/¹⁴⁴Nd ratio, which propagate to the uncertainty of ε¹⁴³Nd. Additionally, the ε¹⁴³Nd values are biased by the presence of secondary Nd of unknown age and isotopic composition in more altered zircons. The ¹⁴⁷Sm-¹⁴³Nd system is more promising as a gauge for this secondary, alteration-related REE component in zircon. Application of the ¹⁴⁶Sm-¹⁴²Nd system in zircon to determine the timing of early terrestrial differentiation is promising. It will require advancement of the analytical procedures to achieve the lowest possible blanks and maximum sensitivity. Ion yield as high as 20-30% will be required.