Thirty six samples of lava from seven of the Hawaiian volcanoes have been dated by the K-Ar method. The results show that the order of extinction of the volcanoes, excluding minor activity after the main shield-building phase was completed, occurred along the island chain from northwest to southeast. All the lavas are late Pliocene and Pleistocene, excepting the Mauna Kuwale trachyte, which is early to middle Pliocene. The exposed parts of the volcanoes dated were built in less than 0.5 m.y., with the exception of the Waianae volcano of West Oahu, which was active over more than 0.7 m.y., and Kauai, which was active over more than 1.8 m.y. The thin veneer of alkali lavas of the main shield-building phase generally is less than 0.2 m.y. younger than the underlying “primitive” basaltic lavas, of which the Hawaiian volcanoes are mainly built.

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