Fig. 3

Δ³³S vs δ³⁴S for clinopyroxene- and spinel-hosted sulphide inclusions from El Hierro (coloured symbols, this study), compared to other OIB (grey symbols). The majority of inclusions have mss compositions close to pyrrhotite (yellow symbols, group 1), but some also contain Cu-rich iss intergrowths (orange symbols, group 2), while others display quench textures with low EPMA totals (~95%; dark red symbols). The δ³⁴S range is comparable to that of the silicate melt, with the most negative values reached by the 2-phase and heterogeneous sulphides. Δ³³S values cluster around 0‰ (i.e. within the mass-dependent fractionation line), contrasting with the Mangaia sulphides (grey squares; ref. ⁴) and Pitcairn sulphides (grey triangles; ref. ⁵) but similar to St. Helena glass⁵². The MORB field (black square; ref. ⁵⁴) is shown for comparison. The modelled effect of degassing (Fig. 2a) follows the negative x-direction at Δ³³S = 0 (i.e. the terrestrial mass-dependent fractionation line). Error bars are 1σ propagated analytical uncertainties