Extended Data Fig. 5: Great circle distance (km) from active hotspot center vs. ¹⁴³Nd/¹⁴⁴Nd (not age-corrected) for hotspot tracks with and without plume-ridge interaction.

A) Rurutu-Arago, B) Louisville-Ellice Basin Seamounts, and C) Hawai‘i-Emperor hotspot tracks. Isochrons are provided as dashed lines, and light grey fields mark where the plumes interacted with ridges or fracture zones. All three hotspot tracks record significant variability in isotopic composition over time that correspond to interaction of the plume with major lithospheric structural features. Rurutu-Arago, which was a true-intraplate hotspot for the entirety of its documented history, produced episodes of depleted (high ¹⁴³Nd/¹⁴⁴Nd) melts that coincide spatially with major lithospheric structures, but otherwise maintains a fairly constant ¹⁴³Nd/¹⁴⁴Nd over time. Samples with evidence of phosphatization (high Y/Y* and/or P₂O₅; see Extended Data Fig. 10) are shown as light grey circles with red outlines. Black circles with red outlines are samples that may have been phosphatized (¹⁴³Nd/¹⁴⁴Nd > ~0.5131) but cannot be confirmed due to lack of available major and trace element data. By contrast, the Louisville hotspot track, including the Ellice Basin Seamounts, records a long-term trend of enrichment with time that records its transition from plume-ridge interaction to true intraplate. Deviations also occur when the plume crossed the Osbourn Trough (however, it remains unclear whether this is related to the Louisville plume), and later the Wishbone Scarp (attributed to source mantle heterogeneity^29,64). The broad enrichment trend in Louisville is similar to long-term enrichment observed in the Hawaiian plume, which also interacted with a ridge in the Cretaceous before transitioning to a true-intraplate plume system¹¹². Data sources are the same as in Fig. 1.