Time steps of depletion and enrichment in the Kaapvaal craton as recorded by subcalcic garnets from Finsch (SA)

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

“…All analyzes were carried out at Frankfurt University; the major elements by electron probe micro analysis (EPMA), the trace elements by laser ablation inductively coupled plasma mass spectrometry (LA ICP MS) and the Lu-Hf and Sm-Nd isotope systems by solution-mode multiple collector ICP MS (MC ICP MS). The detailed procedures and analytical errors are already published by Lazarov et al (2009) and Shu et al (2013). A summary is provided in the electronic appendix.…”

“…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.…”

“…2); other garnets have LREE depleted patterns that are flat or negatively sloping from middle to heavy REE, with Lu and Yb contents higher than the sinusoidal garnets. Garnets were divided into groups at each locality depending on the relative abundances of the middle and heavy REE and their Zr and Hf systematics (Lazarov et al, 2009 andShu et al, 2013). L2 and L3 garnets from Lace are the only groups with positive Zr, Hf and Ti anomalies; RV3 garnets from Roberts Victor have minor negative or no Zr-Hf anomalies.…”

“…We extend their studies of subcalcic garnets to one further group each from Roberts Victor and Lace and to two further diamond mines, Bellsbank and Bultfontein (Kimberley), and discuss the new data together with those of Lazarov et al (2009) andShu et al (2013). We focus on the nature and origin of the metasomatizing agents in the subcratonic mantle as documented by these garnets and quantify the degree of metasomatism necessary to generate the various REE and trace element systematics of the subcalcic garnets.…”

“…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).…”