Figure 3

Noble gases isotopes ratios obtained by crustal crushing from lavas and cumulates. (a) ⁴He/⁴⁰Ar* vs. Rc/Ra modelling the effect of diffusion (green dashed lines; the star highlights the effect of the diffusion on a crystal of 0.5 or 1 cm of diameter after 2 or 8 years, respectively) and the combined effect of magma aging and degassing (black dashed lines). The extent of degassing is reported (e.g., percentage). (b) ⁴He/⁴⁰Ar* vs. Rc/Ra modelling the effect of degassing, gas flushing and melt mixing resulting from the melting/degassing of two distinct components of the mantle plume below La Réunion island. The part of the plumbing system where the volatile phase is exsolved (starting conditions) to generate gas flushing in the upper parts is characterised by its average ⁴He/⁴⁰Ar* value¹⁰: (0) oceanic crust, (1) mantle-crust underplating layer, (2) deep melt horizon and (3) mantle source. The extent of gas flushing is reported (e.g., percentages). See Methods for supplementary information on the modelled curves. Same legend than for Fig. 2. Dark grey field for previous data at PdF. The meaning of σ_error and σ_replicates is detailed in the Methods and the caption of Fig. 2.