Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia): Geochemical dependence on the age of the lithosphere

Basaltic volcanics from Mururoa, Fangataufa and Gambier islands, which belong to the Pitcairn island chain, have been studied for trace elements and Sr, Nd and Pb isotopic composition. While the trace element ratios remain constant, the ⁸⁷Sr/ ⁸⁶Sr ratios range from 0.70292 to 0.70367, ¹⁴³Nd/ ¹⁴⁴Nd ranges from 0.51303 to 0.51288 and the ²⁰⁶Pb/ ²⁰⁴Pb isotopic composition ranges from 18.99 to 19.62. These values, which are clearly distinct from those of Pitcairn basalts, vary according to distance from the present hot spot and are correlated with the age of the underlying lithosphere. It is suggested that the basalts studied were produced by variable degrees of partial melting from an oceanic lithospheric plate metasomatized by prior passage over the Easter hot spot.