title: Eclogitic diamond formation at jwaneng: No room for a recycled component
abstract: Eclogitic diamonds have a large range of delta13C values, whereas peridotitic diamonds do not. Paired delta15N-delta13C-N variations in 40 eclogitic diamonds from the Jwaneng kimberlite in Botswana show that neither the influence of recycled biogenic carbon nor the global and primordial heterogeneity of mantle carbon are likely for the origin of the large delta13C range; the data instead support a fractionation process. It is proposed that carbonatitic mantle melts from which diamonds crystallize undergo different evolutions before diamond precipitation, when percolating through either a peridotite or an eclogite. These different evolutions, reflecting the presence or absence of olivine, can account for their respective delta13C distributions.
authors.affiliation: P. Cartigny and M. Javoy, Laboratoire de Geochimie des Isotopes Stables, Universite de Paris VII, Institut de Physique du Globe de Paris (IPGP), 4 Place Jussieu, 75251 Paris Cedex 05, France. J. W. Harris, Department of Geology and Applied Geol.
authors.initials: P
authors.lastname: Cartigny
authors.initials: JW
authors.lastname: Harris
authors.initials: M
authors.lastname: Javoy