Samoa reinstated as a primary hotspot trail

Abstract

The classical model for the generation of hotspot tracks maintains that stationary and deep-seated mantle plumes impinge on overriding tectonic plates, thereby generating age-progressive trails of volcanic islands and seamounts. Samoa has played a key role in discrediting this model and the very existence of mantle plumes, because early geochronological work failed to demonstrate a linear age progression along this chain of islands. Specifically on Savai9i Island, the bulk of the subaerial volcanics is younger than 0.39 Ma, much younger than the 5.1 Ma age predicted from the classical hotspot model and a constant 7.1 cm/yr Pacific plate motion. This discrepancy led to alternative magma-producing mechanisms that involve the cracking of the lithosphere beneath the Samoan islands, as a result of the extensional regime generated by the nearby Tonga Trench. Here we report 40 Ar/ 39 Ar ages from the submarine flanks of Savai9i Island showing that its volcanic construction began as early as 5.0 Ma and in a true intraplate setting. This reinstates Samoa as a primary hotspot trail associated with a deep mantle plume and a linear age progression.