Figure 2: Selected major oxide and incompatible element compositions of low-Ti Manihiki rocks and glasses.

(a) MgO versus SiO₂ and (b) MgO versus TiO₂ plots for low-Ti Manihiki glasses (red circles) and whole rock samples (white circles: this study, Supplementary Table 2; grey circles: data from refs 4, 13). All major element oxide data were normalized on a volatile-free basis to 100%. Compositional fields for Tonga and Troodos boninites^26,27, Kroenke/Kwaimbaita OJP rocks and glasses^6,15, melt inclusions from Ontong Java¹⁶ and Pacific MORB⁶⁶ are shown for reference. Compositional range of boninites (>52 wt% SiO₂, >8 wt% MgO and <0.5 wt% TiO₂) is shown by grey field with dashed outer line¹⁴. (c) Incompatible element contents in low-Ti Manihiki glasses (black patterns), high-Ca boninites from Tonga (green patterns) and Troodos (blue patterns) normalized to N-MORB. (d) Rare earth elements in the same samples normalized to chondritic abundances. Most low-Ti glass samples from Manihiki have U-shaped patterns similar to boninites, reflecting in part re-enrichment of the most incompatible elements in a depleted source. Direct comparison of incompatible elements shows that boninite-like low-Ti Manihiki glasses do not show enrichment in fluid-mobile elements or negative Nb-Ta anomalies characteristic of boninites. Representative compositions for Troodos and Tonga boninites^67,68 and OJP Kroenke-type rocks (OJP Kroenke; yellow field)⁶ are also shown. OJP inclusions¹⁶ in d have similar labelling as in a,b. N-MORB and chondrite compositions for normalization are from ref. 32.