洋壳俯冲形成的汇聚型板块边缘是长英质地壳形成的主要场所，往往也孕育大型斑岩型铜金矿床，其成矿属性通常与较高的挥发份和高氧逸度有关。项目申请人参与的2018年国际大洋发现计划376航次通过深海钻孔采集了Kermadec岛弧带上的Brothers火山样品，其主要科学目的之一即是探究大洋岛弧火山的岩浆-热液系统和相关金属矿床的成因联系。初步研究显示火山喷发产物具有高Cl和成分复杂多变的特点，可能对于浅部热液系统的高盐度卤水和金属成矿潜力具有决定作用。本研究在分析统计火山岩斑晶和熔体包裹体的主要元素含量的基础上，重点利用原位分析技术测定原始的和均一化的熔融包裹体的挥发份和金属元素的含量，并且采用高温高压实验模拟此类岛弧岩浆的结晶分异过程及金属成矿元素的分配迁移。本研究将深化我们对大洋岛弧岩浆演化及其与斑岩型铜金矿床成因联系的认识。

Convergent plate boundaries formed by subduction of oceanic crust are the major geological setting on Earth that produces juvenile felsic continental crust, as well as large-scale porphyry (and associated epithermal) Cu-Au deposits. One of the main goals of International Ocean Discovery Program (IODP) Expedition 376 (conducted in May–July 2018, PI was a scientific participant) was the understanding of the magmatic-hydrothermal system and associated metal ore deposits (e.g., Cu+Au) at intra-oceanic 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 arc magmas are characterized by high Cl concentrations and a large compositional variability, which are expected to have important contributions to the overlying submarine hydrothermal system that shows high-salinity fluids and magmatic-sourced mineralization in Cu, Au and other rare metals. 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 general 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 phenocrysts and melt 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, Au) enrichment will be estimated based on trace element analysis of melt inclusions. Most melt inclusions contain quench crystals and bubbles and need to be re-homogenized at high temperature and 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.