Fig. 2: Variations in δ⁶⁶Zn versus SiO₂ (a) and La/Sm (b) for HIMU basalts.

All samples in a have high MgO contents (MgO>8 wt.%). Therefore, all samples shown in a are less-evolved samples and are suitable for discussion about the nature of its mantle source. Classic HIMU OIBs are shown by yellow (Cook-Austral samples) and blue circles (St. Helenea samples). Zinc isotopes and other geochemical data (major and trace elements) of HIMU basalts can be found in Supplementary information, Note 1, Supplementary Table 1.1 and Supplementary Table 7. Estimated δ⁶⁶Zn values of the peridotitic mantle are taken from ref. 27. δ⁶⁶Zn values of samples from continental nephelinite, MORB and other OIBs are also shown (Data are from refs. 21,22,23, 29,30,31). The black arrow in a points to the direction of increasing contribution of recycled carbonates. Error bars on δ⁶⁶Zn represent 2 standard deviations (2 SD) uncertainties. The gray line in b represents model calculations for melts of peridotite. The green line represents model calculations for melts of refertilized peridotite. Silicic melts released from recycled oceanic crust metasomatize normal peridotite and therefore produce such refertilized peridotite, as mentioned in Herzberg et al.⁴¹. The pink and blue lines represent model calculations for melts of pyroxenite and carbonated peridotite, respectively. Inset numbers indicate the degrees of partial melting. See Supplementary information, Note 4 for more details about model calculations of mantle partial melting. MORB = Mid-Ocean Ridge Basalt; OIB = Ocean Island Basalt; HIMU = high μ (μ = ²³⁸U/²⁰⁴Pb).