Geochemistry of lavas from the Ahu and Tupa volcanic fields, Easter Hotspot, southeast Pacific: Implications for intraplate magma genesis near a spreading axis

Lavas from two young volcanic fields of the Easter Hotspot consist mainly of enriched tholeiites, with incompatible element and isotopic compositions similar to enriched MORB from the neighbouring spreading axis. The major element composition of these intraplate tholeiites suggests that they originate from melting at greater pressures, and REE models indicate slightly lower degrees of partial melting than beneath the ridge. This can be explained by the thickening of the lithosphere away from the spreading axis, accompanied by increasing mantle temperature as the Easter plume is approached. These processes combine to depress the melting zone to greater depth in the intraplate region. The relatively low degrees of partial melting and low volumes of melt compared, for example, to Galapagos imply a low excess temperature (∼ 100°C?) for the Easter plume. A few depleted tholeiites found on the Ahu volcanic field were generated by shallow melting of an extremely depleted (more depleted than MORB mantle) source.