Figure 22. 4He/3He ratios and 3He concentrations in different rocks and Complexes. Notice variations of both parameters within a factor of 1,000 implying that the rate of melt degassing and subsequent retention of trapped He are the principal factors controlling observed 4He/3He ratios. The parent elements, U and Th, vary on a much narrower scale (Table 3) and cause limited variations of 4He/3He (Figure 23). Solid - ultrabasic, shadowed - alkaline, open - carbonatitic rocks, numbers are numbers of samples.