Zn-, Mg- and O-isotope evidence for the origin of mantle eclogites from Roberts Victor kimberlite (Kaapvaal Craton, South Africa)

Abstract We report Zn-isotope compositions of garnet, clinopyroxene, and whole rocks for 14 Type I 10 II eclogites from the Roberts Victor kimberlite (Kaapvaal Craton, South Africa) that were previously analyzed Mg-O isotopes. are protoliths highly metasomatized I. Garnet clinopyroxene in have δ66Zn 0.14‰ to 0.50‰ 0.29‰ 0.58‰, respectively; reconstructed whole-rock is 0.24‰ 0.54‰, which higher than typical mantle values (0.16–0.20‰). Their heavy Zn- light Mg- O-isotope (δ26Mg = −1.1‰ −0.14‰, δ18O 2.3‰ 4.9‰) cannot originate subducted, carbonate-rich, altered oceanic crust, enriched Zn-O Mg The low may be inherited parental melts derived low-δ18O sources like those produced Weltevreden komatiites Kaapvaal Craton. high δ26Mg reflect diffusion-driven Zn-Mg–isotope exchange between peridotites during their emplacement deep lithosphere. 0.03‰ 0.43‰ garnet 6‰ 9.1‰ but show more scatter inter-mineral fractionation II, reflecting incomplete equilibration later metasomatism by carbonatitic-to-kimberlitic melts. Our evidence multiple isotopes thus suggests might crystallized deep-seated at depths.