Isotopic constraints on the Easter Seamount Chain source

New isotopic data (Sr, Nd and Pb) for lavas from Easter and Salas y Gomez I slands, and nine seamounts along the length of the Easter Seamount Chain (E SC) to the east of these islands, exhibit a regular behavior that is consis tent with two-component mixing between a MORB-like source and more enriched mantle (the Easter Plume source) characterized by relatively radiogenic Pb and unradiogenic Sr. Based on the linearity of mixing trends on the isotop e diagrams, the plume source appears to have maintained approximately the s ame isotopic composition over the 20 to 30 Ma history of the Easter Plume s ampled by the seamounts. In current nomenclature, the plume source resemble s a mix of predominantly HIMU mantle with a small amount of EMI. The propor tions of MORE and plume source mantle sampled by the lavas erupted along th e ESC vary in a systematic way, with Easter Island and seamounts to the wes t containing larger fractions of the MORE component than Salas y Gomez Isla nd and the older seamounts to the east. This variability is probably a refl ection of the nearness to the spreading center, and therefore lithospheric thickness, at the time of volcanism.