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次考察(于2018年进行)的主要目标是了解大洋内火山弧的岩浆-热液系统和相关的金属矿床(例如，铜+金)。这次探险的重点是对克尔马德克弧的兄弟火山进行采样，该火山产生了演化的英安岩到流纹岩熔体，与克尔马德克弧沿线的其他几个火山系统形成了鲜明对比。兄弟火山还具有极富氯的特殊性，具有很大的成分变异性(如碱和氧化铝含量，Mg#)，这一提议的目的是揭示岩浆室衍生的挥发性相(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馏趋势和金属富集的影响。这一目标将通过三个相辅相成的分析和实验任务来实现：1)长英质岩浆的来源，分馏和分异过程将基于基质玻璃和玻璃包裹体的主元素分析，2)岩浆储存条件和挥发分，特别是Cl和H2O在岩浆分馏中的作用将受到高压结晶实验的制约；3)基于斜长石和单斜辉石中玻璃包裹体的微量元素分析，将估计挥发分和氧逸度对矿石金属(如Fe、Cu、Zn、W、Au)的富集性。大多数玻璃包裹体含有淬火晶体和气泡，需要在高压下重新均化。这三个工作包的结合将使我们能够跟踪分异过程中和岩浆-热液阶段富氯岩浆系统中金属浓度的演变。

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.