Behaviour of Igneous Systems and Metal endowment across Arcs (BISMArc)

弧形地壳裂谷可能拥有大型热液系统，有可能形成具有经济意义的大型矿藏。跨弧进入弧后环境的高度多变的构造和岩浆条件为研究各种岩浆和热液系统提供了独特的机会(例如，Hannington等人，2005年)。在这里，我们旨在量化从弧前到弧后转变过程中熔化制度(物理条件、熔化和地幔来源)的变化及其对金属势能的影响。岛弧火山已知岩浆挥发分对(成矿)热液的直接贡献，但氧化态、硫饱和度和岩浆脱气对硅酸盐熔体中金属行为的普遍联系仍是一个活跃的争论问题。Jenner等人。(2010、2015)指出了磁铁矿结晶的开始对硫饱和以及亲硫元素行为的重要性。然而，它们的磁铁矿危机可能仅限于特定的物理化学环境(如闭合体系行为、氧化状态和熔体组成等)。并需要在不同的岩浆系统(例如从弧到弧后的过渡)和空间分辨率下进行研究。在这里，我们旨在弄清地幔来源和熔融对熔体和挥发分中金属富集度的影响，以及与资源勘探相关的规模的熔体和挥发分路径的地质框架。该项目包括两个分项目，一个侧重于提供基本框架的地幔来源、熔融条件和岩浆分异，另一个侧重于海底地质(上升路径和地球动力学)以及金属(特别是铜、金和所谓的关键金属)和熔体中挥发物(水、二氧化碳、氯、S)的独特行为。然而，这两个项目是紧密相连的(特别是通过岩浆演化方面)，需要密切合作和频繁交流。这项研究的重点将是汤加-克尔马德克俯冲系统，在那里可以随时获得大量样本材料，最近又批准了另外两次研究巡航(阿基米德一号和汤加RIFT号)。

Rifting of arc crust may host large hydrothermal systems with the potential of forming large mineral deposits of economic relevance. The highly variable structural and magmatic conditions across arcs into the backarc environment provide a unique opportunity to investigate a large diversity of magmatic and hydrothermal systems (e.g., Hannington et al., 2005). Here, we aim at quantifying both the changes in the melting regime (physical conditions, melting and mantle sources) in the transition from arc front into backarc and the impact on metal potential. A direct contribution of magmatic volatiles to (ore-forming) hydrothermal fluids is known from island arc volcanoes but the general links between oxidation state, sulphur saturation and magmatic degassing on metal behaviour in silicate melts are still a matter of active debate. Jenner et al. (2010, 2015) pointed at the importance of the onset of magnetite crystallization for sulphur saturation and thus chalcophile element behaviour. However, their magnetite crisis may be restricted to specific physicochemical circumstances (such as closed system behaviour, oxidation state and melt composition etc.) and needs to be investigated in different magmatic systems (e.g., arc to backarc transition) and spatial resolution. Here, we are aiming at disentangling the influence of mantle sources and melting on the metal enrichment in melts and volatiles and the geological framework of pathways for melts and volatiles at a scale that is relevant to resource exploration. This project consists of two sub-projects, one with an emphasis on mantle sources, melting conditions and magmatic differentiation providing the basic framework and the other focused on seafloor geology (ascent paths and geodynamics) and the distinct behaviour of metals (especially Cu, Au and the so-called critical metals) and volatiles (H2O, CO2, Cl, S) in the melts. However, these two projects are closely linked (especially through the aspect of magma evolution), requiring close collaboration and frequent exchange. The focus of this study will be on the Tonga-Kermadec subduction system, where extensive sample material is readily available and two additional research cruises have been recently approved (ARCHIMEDES I and TongaRIFT).