Evolution of the South African mantle—a case study of garnet peridotites from the Finsch diamond mine (Kaapvaal craton); Part 2: Multiple depletion and re-enrichment processes

Ancient mantle metasomatism recorded in subcalcic garnet xenocrysts: Temporal links between mantle metasomatism, diamond growth and crustal tectonomagmatism

“…Jordan, 1975). These melts migrate upwards to further metasomatize peridotite while the residual mantle is destroyed (Lazarov et al, 2012). The time of thermal consolidation and cratonization occurred before 2.5 Ga, probably in the time interval between 2.7 and 3.3 Ga as indicated by the age range for metasomatism from the Lu-Hf isotope system and the spread in Re-Os model ages (see Fig.…”

“…Lazarov et al, 2009Lazarov et al, , 2012Shu et al, 2013), T RD and T MA Re-Os model ages of peridotites and sulfides, and sulfide Re-Os isochrons Richardson et al, 1984;Pearson et al, 1995;Jacob et al, 1998) and garnet inclusions in diamonds (= diamonds from Richardson et al, 1984;Richardson and Harris, 1997) in a εNd (0) versus 147 Sm/ 144 Nd diagram. This kind of "isochron" diagram shows (i) the very negative εNd (0) that are common to subcalcic garnet xenocrysts and garnet inclusions in diamonds, (ii) that multiple overprints affected the majority of the subcalcic garnets (large spread to less negative and positive εNd) whereas the inclusions have only negative values and (iii) reliable age information may be obtained only from individual localities.…”

“…The ages for crustal tectonomagmatic events are taken from summaries by Eglington and Armstrong (2004) and Schmitz et al (2004). Ages for mantle metasomatism are from the present work and previous work by Lazarov et al (2009Lazarov et al ( , 2012 and Shu et al (2013). Ages for the growth of diamond are from summaries by Pearson and Wittig (2008), Stachel and Harris (2008) and Gurney et al (2010).…”

“…Zhang et al, 2000). Archean to Proterozoic ages were obtained for metasomatism in the Kaapvaal subcratonic lithospheric mantle by Lazarov et al (2009Lazarov et al ( , 2012 and Shu et al (2013) through the application of the Sm-Nd and the Lu-Hf isotope systems to single grain subcalcic garnets from the Finsch, Roberts Victor and Lace diamond mines (Fig. 1).…”

Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts

“…A negative array is also present between δ 57 Fe and hafnium isotopes (εHf; Fig. 3d), a radiogenic isotopic system that records the timeintegrated fractionation of Hf from Lu during partial melting and which has been shown to be generally resistant to overprint by mantle metasomatism (Bizimis et al, 2004;Lazarov et al, 2012;Stracke et al, 2011). While Fe stable isotopes do not record temporal information, the observed correlation between Fe isotopes and Hf isotopes does suggest that the samples with the greatest radiogenic isotope signatures of time-integrated melt extraction are also the most isotopically fractionated in terms of Fe.…”