METGAS [ANR]

The release of metals associated with magmatic degassing is a critical process in Earth Sciences that is not only key to the development of early life on Earth or the formation of many ore deposits but may also have negative environmental impacts (e.g. release of heavy metals in high concentrations to the hydrosphere and atmosphere), which are yet to be accurately constrained on a worldwide scale.

The efficiency and extent of metal degassing is expected to vary significantly depending on geodynamic setting (volcanic arcs, intracontinental rifts or hotspots) as it mostly depends on 1) melt composition, 2) pressure (P), temperature (T) and redox conditions of magmatic degassing and 3) the effect these parameters have on the concentration of Cl or S that complex with metals in the magmatic fluids. Yet, the actual mechanisms behind metal transport by magmatic fluids and gases remain poorly understood, as these phases are both difficult to sample in nature and synthesize in the laboratory. This in turn limits our ability to simulate metal magmatic degassing, be it in the context of ore deposit formation around magmatic intrusions or of volcanic emissions at the Earth’s surface.

The main goal of the METGAS project is thus to investigate the fluid-melt partitioning and speciation of economic or harmful metals (Cu, Zn, Pb, Hg, Se and Te) in high-temperature fluids and gases. To do so, we propose to combine cutting-edge experimental and analytical approaches at the Institut des Sciences de la Terre d’Orleans and the ESRF synchrotron in Grenoble to 1) analyse high P-T fluids down to the molecular level via in-situ Raman and x-ray spectroscopy and 2) trap them as frozen droplets for further laser ablation ICPMS analyses. We will then use our experimental results to simulate the metallic discharge associated with Kilauea (Hawaii, USA) long-term degassing and Mount Pinatubo (Philippines) 1991 cataclysmic Plinian eruption. Together, our experimental results and degassing simulations will constitute a first-hand database for the thermodynamic modelling of metal uptake and transport by magmatic fluids as a function of their magmatic source and the P-T conditions of degassing and hence pave the way towards modelling of metal degassing at a world-scale.