Melt inclusions (MIs) represent pristine melt droplets trapped in early forming phenocrysts, which record the variable physico-chemical conditions of their hosting system. Compared to whole rock studies, the MIs approach shows advantages especially because it provides information on melt composition, volatile content, pressure and temperature at well-defined pre-eruptive stage. A large amount of geochemical data is available for the magmas generated in the Phlegraean Volcanic District (PVD), which is one of the most densely populated and high-risk volcanic areas of the world, but the knowledge provided by those data on their plumbing system, ascent, degassing and extrusion is limited. We investigated the glass/melt inclusions in olivines from the Solchiaro 1 volcanics, erupted on Procida Island, which is located along main tectonic alignment of the PVD. These products represent the least evolved magma of the PVD and could testify for the presence of the “basic” and deepest reservoir from which the Phlegraean magmas upraised and differentiated through various steps. Often invoked in literature, this “primitive” reservoir is basically uncostrained. We performed microprobe and microscopy measures to determine textural and compositional features of the MIs and host-minerals. The measures by Fourier Transform InfraRed spectroscopy provided the content of dissolved H2O and CO2, hence the volatile budget of magmas and entrapment pressures (i.e. depths of crystal growth). Recalculated crystallization depths for the Solchiaro 1 olivines result to be very deep (~350 MPa) and isobars obtained for the MIs describe a degassing trend with high CO2 content, of deep origin. Taking into account the geophysical data and the MIs studies on other Phlegraean products recently published, our dataset depicts a new framework for the evolution of the PVD plumbing system up to the present time that improves both the comprehension of magma evolution and migration through various reservoirs and the volcanic hazards assessment.
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