Ages isotopiques K/A de roches prelevees dans les possessions francaises du Pacifique

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Abstract
The authors present some forty age determinations made by the K/Ar method on the volcanic rocks of Tahiti and the archipelagoes of French Polynesia by means of a Philips omegatron. The results obtained may be divided grossly into three groups: sub-Recent ages (from 0 to 3 m.y.); Mio-Pliocene ages (about 10 to 15 m.y.) and an age of about 150 m.y., given by a granular inclusion in a nephelinic gabbro-diorite from the center of the island of Tahiti. The last age is particularly interesting because no fossiliferous formations older than Cretaceous are known in the Pacific. These rocks may thus be older and may date at least from the Jurassic. They accordingly pose the problem of the existence, beneath the present volcanoes, of a much older crystalline basement.

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