Host: Japan Association of Mineralogical Sciences
Subduction zone magmatism is triggered by addition of slab-derived component into overlying mantle wedge. Whether this component is aqueous fluids from dehydration or partial melts of subducting oceanic crust remains an open question. Based on our high-P and high-T radiography experiments at SPring-8, we suggest surprisingly shallow pressures of critical endpoints between aqueous fluids and high-Mg andesite (2.9 GPa, 87 km depth) or sediment (2.5 GPa, 75 km depth). We suggest that slab-derived fluids should be supercritical fluids at the top of subducting slab beneath the volcanic arcs. Under relatively hot conditions, dense liquid-like supercritical fluids are input from dehydrating slab to the overlying mantle wedge. Such dense supercritical fluids produce double magmatism in hot subduction zones by their separation into aqueous fluids and hydrous melts: basalt and sanukite or basalt and adakite.