Anthony A.P. Koppers et al., College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, Oregon 97331-5503, USA. Pages 435-438.
Hotspots are focused regions of anomalous intra-plate volcanism, yet the mechanisms driving this type of volcanism are subject to vigorous debate.
One model assumes that deep-seated mantle plumes drive hotspot volcanism and generate linear age progressions in the hotspot trails they leave behind. These are the so-called "primary" hotspot trails, of which only three have been identified in the Pacific basin. However, the absence of clear age progressions along other hotspot trails has been used as an argument against the role of mantle plumes in seamount trails, favoring models of lithospheric extension and the release of melt from shallow mantle sources or plumelets. In the case of Samoa, the omnipresence of subaerial volcanic rocks younger than 0.39 million years old on Savai'i Island appears to argue against the mantle plume model, because a 7.1 cm/yr Pacific plate motion would predict a hotspot age of 5.1 million years for this volcano.
Koppers et al. present new 40Argon/39Argon data on volcanic samples from the deep flanks of Savai'i Island that confirm the predicted 7.1 cm/yr age progression for the Samoan hotspot. Three different volcanic samples from the deepest portion of the southwest flank of Savai'i Island give ages ranging from 4.99 to 5.21 million years. These results demonstrate that the onset of shield-building on Savai’i occurred much earlier than the oldest 0.39 million-year-old volcanics sampled subaerially on the island. Strontium-neodymium-lead isotopes and trace-element data show that the dredge samples have a typical Samoan shield pedigree and are distinct from the subaerial rejuvenated volcanics on Savai'i and Upolu.
Together, this reinstates Samoa as a hotspot trail with similar characteristics as the "primary" Hawaiian and Louisville hotspot trails. It eliminates the major argument against a plume origin for Samoa.-Geological Society of America
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