Figure 14. Helium isotope abundance in samples from Kola ultrabasic-alkaline-carbonatite Complexes: a fluid component (gas extraction by milling). Both 4He/3He ratios and 3He concentrations in vesicles vary within ~4 orders of magnitude. The lowest ratios are well below MORB values indicating a contribution of high-3He plume component. The general tendency is the higher 3He concentrations, the lower 4He/3He ratios. A moderate range of 4He/3He ratios in samples greatly enriched with 3He could result from inhomogeneity of trapped fluid or mixing of trapped and in-situ produced He. This dilemma is discussed in Sections 4.1.4 and 5.2. See Figure 11 for sources of MORB and OIB data.