Figure 3: Radiogenic isotopic composition of low-Ti Manihiki rocks.

Initial radiogenic isotope ratio plots (with correction for radiogenic ingrowth to 120 Myr ago) of (a) ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁸Pb/²⁰⁴Pb and (b) ²⁰⁶Pb/²⁰⁴Pb versus ¹⁴³Nd/¹⁴⁴Nd for low-Ti glasses. The stars represent the estimated UDM (red) and enriched (blue) end members for the Manihiki low-Ti tholeiites. The enriched melt end member for the Manihiki low-Ti tholeiites has characteristics similar to HIMU-like OIB lavas from Rurutu and Tubuai⁶⁹ of the Cook-Austral Chain (see discussion, Supplementary Fig. 2 for calculation of the Manihiki-enriched end member). The black lines show mixing of UDM with variable amounts (indicated at tick marks in wt%) of the enriched OIB-like component represented by a mafic Rurutu lava sample from ref. 34. Note: ¹⁴³Nd/¹⁴⁴Nd ratio for intermediate sample SO225DR12-2 was not included for end member calculations (see ‘Sample material’ in the ‘Methods’ section). Isotope data for the Kroenke/Kwaimbaita field were taken from refs 10, 11. The MORB-field data⁷⁰ were projected to 120 Myr using the following parent/daughter ratios from ref. 4: ¹⁴⁷Sm/¹⁴⁴Nd=0.25, ⁸⁷Rb/⁸⁶Sr=0.005, ²³⁸U/²⁰⁴Pb=10, ²³⁵U/²⁰⁴Pb=0.073, ²³²Th/²⁰⁴Pb=40. The Indian MORB⁷⁰ field was projected to 120 Myr using calculated parent/daughter ratios based on the incompatible element composition of E-DMM from ref. 33. The fields for the Tubuai and young Rurutu lavas were also projected to 120 Myr ago and plotted based on compiled literature data and parent/daughter ratios from the calculated OIB source from ref. 36 and references therein.