Figure 5. A schematic model for the formation of the Ontong Java and Manihiki Plateaus from a geochemically heterogeneous mantle-plume head.

The presence of ultra-depleted melts at OJP and Manihiki (UDM) can be explained with a geochemically heterogeneous plume head containing different components beneath the two plateau segments. Beneath OJP, the dominant Kroenke/Kwaimbaita source component upwells and generates the dominant Kroenke/Kwaimbaita basement lavas with flat primitive-mantle-normalized incompatible element patterns. The presumed dominant source component beneath Manihiki is the UDM end member metasomatized by ≤1% HIMU-type melts. We propose that both components beneath Manihiki are derived through recycling of Indian-mantle-like oceanic lithosphere. Ultra-depleted melt inclusions in olivines in a Kroenke sample from OJP¹⁶ indicate that smaller proportions of a possibly common UDM source may also be present beneath the OJP.