Age and Evolution of the Volcanoes of Tutuila, American Samoa

Abstract

Tutuila is a basaltic volcanic island within the east southeasterly trending Samoa Island chain in the Pacific Ocean. Potassium-argon ages on 38 whole rock samples of lavas and intrusives demonstrate that the main period of subaerial volcanism occurred over a relatively short interval of about 0.6 Ma in the Early Pleistocene. The major shield volcano, Pago, was built between about 1.54 and 1.28 Ma ago; its large caldera formed approximately 1.27 ± 0.02 Ma ago. Partial filling of the caldera by volcanics occurred from shortly after its formation until about 1.14 Ma ago, and activity on Pago Volcano ended with emplacement of trachyte bodies which have ages of 1.03 ± 0.01 Ma. Construction of the smaller satellitic Olomoana and Taputapu volcanoes, on the eastern and western extensions of the main rift zone through Pago Volcano, took place over much the same time interval as the volcanism on Pago. The youthful basaltic volcanism on the Manu'a Islands, east of Tutuila, allows a rate of migration of the center of volcanism of about 10cmjyr to be estimated. These results are broadly consistent with a hot spot origin for the volcanoes.