Fig. 4: Correlations of alkalic OIB chemistry with degree of high-pressure crystallization.

a SiO₂ content (b) FeO^T content, and (c) SiO₂/FeO^T ratio averaged for basalt samples from each individual ocean island (ref. ³⁵. and Supplementary Table 3). d Mantle potential temperature estimated by ref. ⁴¹ using seismic observations. e Calculated CO₂ contents in evolved magmas after high-pressure crystallization and melt-orthopyroxene reaction, using the SiO₂-CO₂ correlation in Supplementary Fig. 4. Grey dots, shown for comparison, represent CO₂ contents of individual island groups estimated by ref. ³⁵ according to the averaged Nb or Ba concentrations in their parental melts. f Carbon flux for each island group, calculated based on the CO₂ content in evolved magmas. The C fluxes estimated in this study are higher than that inferred by ref. ⁴⁶ (blue dashed-dot line) and ref. ⁵⁴ (grey dashed-dot-dot line), but located within the inferred ranges by ref. ³⁵ (black dashed lines). Symbols in (a–f) are the same as those in Fig. 1. g–i Factors controlling magma evolution for each island based on our parameterized model. The bar diagrams with numbers above represent mean values of CF (g), RF (h), or \({X}_{C{O}_{2}}^{{Pri}}\) (i). The error bars represent one-standard deviations. The dots in the bars represent the probability density of CF, RF, or \({X}_{C{O}_{2}}^{{Pri}}\). Data on alkalic OIB lavas are the same those as listed in Fig. 1. From left to right, ocean islands are arranged in order of decreasing averaged SiO₂, with the same color coding for SiO₂ contents as in Fig. 1.