It has been proposed that the volcanic islands of French Polynesia (south-central Pacific Ocean) owe their origin either to the activity of several hot spots (plumes) or to propagating tensional fractures. The isotopic composition of strontium has been determined for Miocene to Holocene volcanic rocks from island members of three linear island chains in French Polynesia. A high correlation between Sr87/Sr86 and Rb87/Sr86 is evident and, interpreted as an isochron, indicates that chemical heterogeneities in the mantle source region for these rocks have been maintained for one billion years or more. This ancient age implies that the source region is divorced from the source regions for ocean-floor basalts.

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