Giuliani Gaston auteur aut IRD Pivin M. auteur aut IRD Fallick A. E. auteur aut IRD Ohnenstetter D. auteur aut IRD Song Y. auteur aut IRD Demaiffe D. auteur aut IRD text journalArticle eng text/pdf born digital access Oxygen isotope signatures of ruby and sapphire megacrysts, combined with trace-element analysis, from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China, provide clues to specify their origin in the deep Earth. At Mbuji-Mayi, pink sapphires have 8180 values in the range 4.3 to 5.4 parts per thousand (N=10) with a mean of 4.9 +/- 0.4 parts per thousand, and rubies from 5.5 to 5.6 parts per thousand (N=3). The Ga/Mg ratio of pink sapphires is between 1.9 and 3.9, and in rubies, between 0.6 and 2.6. The blue or yellow sapphires from Changle have delta O-18 values from 4.6 to 5.2 parts per thousand, with a mean of 4.9 +/- 0.2 parts per thousand (N=9). The Ga/Mg ratio is between 5.7 and 11.3. The homogenous isotopic composition of ruby suggests a derivation from upper mantle xenoliths (garnet lherzolite, pyroxenite) or metagabbros and/or lower crustal garnet clinopyroxenite eclogite-type xenoliths included in kimberlites. Data from the pink sapphires from Mbuji-Mayi suggest a mantle origin, but different probable protoliths: either subducted oceanic protolith transformed into eclogite with delta O-18 values buffered to the mantle value, or clinopyroxenite protoliths in peridotite. The Changle sapphires have a mantle O-isotope signature. They probably formed in syenitic magmas produced by low degree partial melting of a spinel Iherzolite source. The kimberlite and the alkali basalt acted as gem conveyors from the upper mantle up to the surface. specialized Oxygen isotopes Chemistry Corundum Kimberlite Alkali basalt Origin Mantle REPUBLIQUE DEMOCRATIQUE DU CONGO CHINE 064 347 1 24-34 2015 1631-0713 https://www.documentation.ird.fr/hor/fdi:010064156 10.1016/j.crte.2014.12.003 1631-0713 [F B010064156] https://www.documentation.ird.fr/hor/fdi:010064156 https://www.documentation.ird.fr/intranet/publi/2015/05/010064156.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2015-06-04 2017-08-23 fdi:010064156 fre