Magmatic evolution of an oceanic island arc – The New Hebrides case

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The magmatic evolution of oceanic island arcs and their potential implications for subduction initiation received much attention recently with the IODP expeditions 350, 351, and 352 in the Izu-Bonin-Mariana (IBM) arc, forearc and rear-arc dedicated to test existing models. Most of the ideas on subduction initiation are thus based on the IBM arc but it is unknown whether these can be applied also to other oceanic island arcs. The New Hebrides island arc (NHIA) is one of the youngest arcs on Earth and formed by subduction initiation following polarity reversal of the subducting plate after the collision of the Ontong Java Plateau some 15 million years ago. Leg 134 of the ODP drilled seven cores with lengths of up to 1100 m in the New Hebrides forearc and backarc and recovered magmatic rocks samples as well as ash layers ranging to the Mid-Miocene. We suggest to re-analyse the rock samples from this ODP Leg as well as other poorly analysed submarine samples from dive and dredge cruises in order to compare the magmatic evolution of the NHIA to the IBM. Additionally, we propose sampling of the central NHIA to establish the magmatic evolution of the old island arc crust to 20 Ma. The new data set will also provide insights into the magma evolution of the NHIA following the subduction of the d’Entrecasteaux island arc that occurred some 2 Ma ago. Our proposed project has important implications for the global understanding of subduction processes and the associated magma formation in the upper mantle.