To better understand and quantify the Iodine contribution of volcanic systems to the atmosphere, we propose to study Iodine partitioning in almost-natural subduction related systems using natural basalt and synthetic trondhjemite both coexisting with a I-enriched hydrous fluid. We will determine the Iodine content for all phases in situ during successive decompression of the system. It will allow us to calculate partition coefficients and to estimate magmatic Iodine fluxes. we will better understand the process of Iodine-release from the melt during its ascent and magmatic degassing. Furthermore, the results can give insight to the Iodine content in magmatic systems. For the first time, we will use a natural basaltic rock for these types of experiments on Iodine. To reach the solidus of the basalt we will also for the first time combine a modified Bassett type hydrothermal diamond anvil cell with a laser heating system.