Chlorine stable isotopes in carbonatites: Evidence for isotopic heterogeneity in the mantle

Eight carbonatite samples were analysed for delta(17)Cl and for delta(18)O and delta(13)C. Th, results show that unaltered carbonatites have delta(37)Cl ratios between -0.8 and +0.1 parts per thousand. Because the whole mantle delta(37)Cl value is approximately +4.7 parts per thousand, chlorine for carbonatite is anomalously light. Although it is possible that the source regions for carbonatites represent isotopic anomalous mantle and may reflect contamination by a crustal component, our preferred explanation is that the processes resulting in the accumulation of carbonatite magma cause fractionation of chlorine isotopes.