Abstract

The island of Maupiti is the top of an eroded volcanic shield surrounded by a large lagoon and coral reef. The most important part of this shield is made up of alkali basaltic lavas grading upward into hawaiitic flows. The shield-building event is dated at ca. 4.51 ± 0.04 Ma. A few mugearitic and benmoreitic late dykes were emplaced at 4.21 ± 0.04 Ma. These chronological data are consistent with a Pacific plate motion of 11 cm/year with respect to a fixed Society plume. The Maupiti lava series results from the effects of fractional crystallisation of a parental alkali basalt magma displaying a prominent EM II isotopic and trace element signature, in many ways similar to that of the youngest Society hot spot lavas. This feature suggests that the geochemical signature of the Society plume did not change through time.

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