Application of precise ¹⁴²Nd/¹⁴⁴Nd analysis of small samples to inclusions in diamonds (Finsch, South Africa) and Hadean Zircons (Jack Hills, Western Australia)

¹⁴⁶Sm-¹⁴²Nd and ¹⁴⁷Sm-¹⁴³Nd systematics were investigated in garnet inclusions in diamonds from Finsch (S. Africa) and Hadean zircons from Jack Hills (W. Australia) to assess the potential of these systems as recorders of early Earth evolution. The study of Finsch inclusions was conducted on a composite sample of 50 peridotitic pyropes with a Nd model age of 3.3 Ga. Analysis of the Jack Hills zircons was performed on 790 grains with ion microprobe ²⁰⁷Pb/²⁰⁶Pb spot ages from 3.95 to 4.19 Ga. Finsch pyropes yield 100 × e{open}¹⁴²Nd = - 6 ± 12 ppm, e{open}¹⁴³Nd = - 32.5, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.1150. These results do not confirm previous claims for a 30 ppm ¹⁴²Nd excess in South African cratonic mantle. The lack of a ¹⁴²Nd anomaly in these inclusions suggests that isotopic heterogeneities created by early mantle differentiation were remixed at a very fine scale prior to isolation of the South African lithosphere. Alternatively, this result may indicate that only a fraction of the mantle experienced depletion during the first 400 Myr of its history. Analysis of the Jack Hills zircon composite yielded 100 × e{open}¹⁴²Nd = 8 ± 10 ppm, e{open}¹⁴³Nd = 45 ± 1, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.5891. Back-calculation of this present-day e{open}¹⁴³Nd yields an unrealistic estimate for the initial e{open}¹⁴³Nd of - 160 e{open}-units, clearly indicating post-crystallization disturbance of the ¹⁴⁷Sm-¹⁴³Nd system. Examination of ^146,147Sm-^142,143Nd data reveals that the Nd budget of the Jack Hills sample is dominated by non-radiogenic Nd, possibly contained in recrystallized zircon rims or secondary subsurface minerals. This secondary material is characterized by highly discordant U-Pb ages. Although the mass fraction of altered zircon is unlikely to exceed 5-10% of total sample, its high LREE content precludes a reliable evaluation of ¹⁴⁶Sm-¹⁴²Nd systematics in Jack Hills zircons.