Nitrogen isotopes in peridotitic diamonds from Fuxian, China: the mantle signature

Abstract

Nitrogen isotopes in peridotitic diamonds from Fuxian, China, suggest that the upper mantle δ 15 N‐value has been globally homogeneous since at least the Proterozoic (−5 to −8‰/ATM), with similar values for subcontinental and MORB mantle. In addition, Fuxian diamonds retain the memory of a primary nitrogen lower in δ 15 N (down to −25‰). For the first time δ 15 N‐ values in diamonds match those of enstatite chondrites, supporting a formation of the Earth from such meteorites and the idea of a heterogeneous accretion 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 grew.