Geochemical data of basalts from the Caroline plate

The mantle under the western Pacific marginal basins is believed to have distinct compositions from that under the bulk of the Pacific Ocean due to isolation by long-lived subduction zones. However, the origin and distribution of such mantle domains beyond these basins remain unclear. The Caroline plate is located between the Pacific plate and the West Philippine Basin, sampling transitional mantle without segmentation by the subduction barrier. Here, we report major and trace element and Sr-Nd-Pb-Hf isotope compositions of basalts from the eastern Caroline plate. These basalts exhibit similar εNd but higher 208Pb*/206Pb* compared to the Pacific mid-ocean ridge basalts (MORBs), and show distinctly higher εHf and Lu/Hf. These signatures, common in western Pacific marginal basin basalts, require melting of an ancient, garnet-bearing, highly-depleted mantle. We propose that this distinct ultra-depleted mantle domain exist inherently under the equatorial western Pacific, possibly linked to mantle plume activities.