NITROGEN ISOTOPES IN PERIDOTITIC DIAMONDS FROM FUXIAN, CHINA - THE MANTLE SIGNATURE

Nitrogen isotopes in peridotitic diamonds from Fuxian, China, suggest that the upper mantle delta(15)N-value has been globally homogeneous s ince at least the Proterozoic (-5 to -8 parts per thousand/ATM), with similar Values for subcontinental and MORE mantle. In addition, Fuxian diamonds retain the memory of a primary nitrogen lower in delta(15)N (down to -25 parts per thousand). For the first time delta(15)N-values in diamonds match those of enstatite chondrites, supporting a formati on of the Earth from such meteorites and the idea of a heterogeneous a ccretion of the Earth's volatiles. Nitrogen concentrations in diamonds are believed to depend strongly on the rate of the diamond growth and not to be an indicator of C/N ratios of the fluids from which they gr ew.