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 tho usand, chlorine for carbonatite is anomalously light. Although it is p ossible that the source regions for carbonatites represent isotopic an omalous mantle and may reflect contamination by a crustal component, o ur preferred explanation is that the processes resulting in the accumu lation of carbonatite magma cause fractionation of chlorine isotopes.