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Giuliani Gaston, Pivin M., Fallick A. E., Ohnenstetter D., Song Y., Demaiffe D. (2015). Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China. Comptes Rendus Geoscience, 347 (1), p. 24-34. ISSN 1631-0713.

Titre du document
Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China
Année de publication
2015
Type de document
Article référencé dans le Web of Science WOS:000353428100004
Auteurs
Giuliani Gaston, Pivin M., Fallick A. E., Ohnenstetter D., Song Y., Demaiffe D.
Source
Comptes Rendus Geoscience, 2015, 347 (1), p. 24-34 ISSN 1631-0713
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.
Plan de classement
Géologie et formations superficielles [064]
Description Géographique
REPUBLIQUE DEMOCRATIQUE DU CONGO ; CHINE
Localisation
Fonds IRD [F B010064156]
Identifiant IRD
fdi:010064156
Contact