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Giving birth to hotspot volcanoes: Distribution and composition of young seamounts from the seafloor near Tahiti and Pitcairn islands

¹ Fachbereich 5—Geowissenschaften, Universität Bremen, D-28334 Bremen, Germany
² Institut für Geowissenschaften, Universität Mainz, Becherweg 21, D-55099 Mainz, Germany, and Max Planck Institut für Chemie, D-55128, Mainz, Germany
³ Laboratoire de Géochemie, Institut de Physique du Globe Paris, place Jussieu, F-75252 Paris Cedex 05, France
⁴ Institut de Physique du Globe, place Jussieu, F-75252 Paris Cedex 05, France
⁵ Laboratoire Pétrologie Structurale, Université de Nantes, F-44322 Nantes, France
⁶ Institut Francais de Recherche pour l'Exploitation de la Mer, F-29280 Plouzané, France
⁷ Institut für Geowissenschaften, Universität Kiel, D-24118 Kiel, Germany

Apart from being popular holiday destinations, oceanic-island volcanoes such as Hawaii, Tahiti, or the Canaries provide magmas that yield valuable information about the interior of our planet. Until recently, studies have concentrated on the easily accessible, subaerial parts of the volcanoes, largely ignoring their earlier-formed, submarine parts. These submarine parts, however, provide critical information about how the mantle begins to melt and about the lowest-melting-point mantle components—information not available from the subaerial volcanoes but highly relevant for the chemical evolution of the whole mantle. We present here compositional information from small (<500 m) volcanoes on the seafloor near Tahiti and Pitcairn Islands and show that these small volcanoes erupt only highly differentiated magmas. These early melts are derived exclusively from the most trace element–enriched, isotopically extreme mantle component, evidence that this component has the lowest melting temperature and is the first product of melting of a new batch of mantle. The geochemical mantle components (enriched mantle EM-I, EM-II) proposed in the 1980s to explain the compositional variations among oceanic volcanoes worldwide appear in reality to represent distinct rock masses in the mantle.

Key Words: Polynesia • geochemistry • plume • enriched mantle • EM-I • EM-II • melting • plum pudding • volcano evolution • hotspot

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