Jean-Baptiste P. auteur aut IRD Allard P. auteur aut IRD Fourré E. auteur aut IRD Bani Philipson auteur aut IRD Calabrese S. auteur aut IRD Aiuppa A. auteur aut IRD Gauthier P. J. auteur aut IRD Parello F. auteur aut IRD Pelletier Bernard auteur aut IRD Garaebiti E. auteur aut IRD text journalArticle eng text/pdf born digital access We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low He-3/He-4 ratios in thermal fluids of Epi (4.0 +/- 0.1 R-a), Efate (4.5 +/- 0.1 R-a) and Pentecost (5.3 +/- 0.5 R-a) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display He-3/He-4 and C/He-3 ratios typical of subduction-related volcanic arcs: He-3/He-4 ratios range from 6.4 +/- 0.5 Ra in southernmost Tanna and 7.23 +/- 0.09 R-a in northernmost Vanua Lava to typical MORE values in the central islands of Gaua (7.68 +/- 0.06 R-a), Ambrym (7.6 +/- 0.8 R-a) and Ambae (7 2 R-a in groundwaters, 7.9 +/- 1.4 R-a in olivine phenocrysts, and 8.0 +/- 0.1 Ra in summit fumaroles of Aoba volcano). On Ambrym, however, we discover that hydrothermal manifestations separated by only 10-15 km on both sides of a major E-W transverse fault zone crossing the island are fed by two distinct helium sources, with different 3He/4He signatures: while fluids in southwest Ambrym (Baiap and Sesivi areas) have typical arc ratios (7.6 +/- 0.8 R-a), fluids on the northwest coast (Buama Bay area) display both higher He-3/He-4 ratios (9.8 +/- 02 R-a in waters to 10.21 +/- 0.08 R-a in bubbling gases) and lower C/He-3 ratios that evidence a hotspot influence. We thus infer that the influx of Indian MORB mantle beneath the central Vanuatu arc, from which Ambrym magmas originate, also involves a He-3-rich hotspot component, possibly linked to a westward influx of Samoan hotspot material or another yet unknown local source. This duality in magmatic He source at Ambrym fits with the bimodal composition and geochemistry of the erupted basalts, implying two distinct magma sources and feeding systems. More broadly, the wide He isotopic variations detected along the Vanuatu arc further verify the complex tectonic and magmatic framework of this intra-oceanic island arc. specialized Vanuatu arc Volcanic fluids Helium isotopes Extinct and active volcanoes Mantle source Hotspot contribution VANUATU 066 062 064 Vergniolle N. ed. edt IRD Métrich N. ed. edt IRD 322 No Spécial 20-29 2016 0377-0273 https://www.documentation.ird.fr/hor/fdi:010068347 10.1016/j.jvolgeores.2015.09.026 0377-0273 [F B010068347] https://www.documentation.ird.fr/hor/fdi:010068347 https://www.documentation.ird.fr/intranet/publi/2016/12/010068347.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2017-01-09 2017-08-23 fdi:010068347 fre