Magmatic volatiles and ore metals released from intraoceanic arc magmas: constraints from high pressure experiments and melt inclusions for Brothers volcano, Kermadec arc

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The main goal of IODP Expedition 376 (conducted in 2018) was the understanding of the magmatic-hydrothermal system and associated metal ore deposits (e.g., Cu+Au) at intraoceanic volcanic arcs. The expedition focused on the sampling of Brothers volcano of the Kermadec arc, that produces evolved dacitic to rhyolitic melts, in contrast to several other volcanic systems along the Kermadec arc. Brothers volcano has also the particularity to be extremely Cl-rich with a large compositional variability (e.g., alkali and alumina content, Mg#) and the aim of this proposal is to unravel the nature and composition of magma chamber-derived volatile phases (e.g., single-phase fluid or two-phase brine and vapor) as well as their effect on fractionation trends and metal enrichment during differentiation.This objective will be achieved with three complementary analytical and experimental tasks: 1) the origin of the felsic magmas, the fractionation and differentiation processes will be investigated based on the major element analysis of matrix glasses and glass inclusions, 2) the magma storage conditions and the role of volatiles, especially Cl and H2O, on the fractionation of magmas will be constrained from high pressure crystallization experiments and 3) the role of volatiles and oxygen fugacity for ore metals (e.g., Fe, Cu, Zn, W, Au) enrichment will be estimated based on trace element analysis of glass inclusions in plagioclase and clinopyroxene. Most glass inclusions contain quench crystals and bubbles and need to be re-homogenized at high pressure. The combination of the three work packages will allow us to track the evolution of metal concentrations in Cl-rich magmatic systems during differentiation and at the magmatic-hydrothermal stage.