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

IODP第376次探险（2018年进行）的主要目标是了解海内火山弧的岩浆-热液系统和相关的金属矿床（例如Cu+Au）。这次考察的重点是对克马德克弧的兄弟火山进行采样，与克马德克弧沿线的其他几个火山系统形成对比，该火山产生演化的英安岩到流纹岩熔体。兄弟火山还具有极富cl的特殊性，其组成变化较大（如碱、氧化铝含量、Mg#），本研究旨在揭示岩浆房衍生挥发相（如单相流体或两相卤水和蒸汽）的性质和组成，以及它们在分异过程中对分异趋势和金属富集的影响。这一目标将通过三个互补的分析和实验任务来实现：1)基于基体玻璃和玻璃包裹体的主元素分析，研究长英质岩浆的成因、分选和分选过程；2)高压结晶实验限制了岩浆的储存条件和挥发物（特别是Cl和H2O）对岩浆分选的作用；3)挥发物和氧逸度对矿石金属（如Fe、Cu、Zn、W、Zn、pb、pb）的作用。通过对斜长石和斜辉石中玻璃包裹体的微量元素分析，估计了Au的富集程度。大多数玻璃夹杂物含有淬火结晶和气泡，需要在高压下重新均匀化。三个工作包的结合将使我们能够跟踪富cl岩浆系统在分化和岩浆-热液阶段的金属浓度演变。

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.