Magmatism of the phlegrean volcanic fields as revealed by melt inclusions

The Phlegrean Volcanic District (PVD) consists of Campi Flegrei (CF), Procida, and Ischia volcanic fields in Southern Italy. The recent unrest crisis of CF at the PVD demands a more detailed understanding of its deep magmatic system to better understand if a new eruption is imminent. Despite the large amount of work published relative to the PVD, there are still many open questions related to (1) the evolution of the magmatic vapor phase (MVP) directly exsolving from magmas at different times and different places below the PVD and (2) the source of this magmatism. Among the investigative tools that can be used to answer these questions about the PVD, melt inclusions (MIs) have been widely used, especially in the last two decades. In this chapter, I compare the MI data from the literature related to CF, Procida, and Ischia, and I highlight three main points based on this comparison. The first is that only a few MI show quasiprimitive composition, and these can be compared to investigate the magma sources below the three different localities of the PVD. This comparison highlights that the same magma source could be present below the three localities of the PVD at different times. The second point is that some of the more evolved MIs show divergence from the bulk rock trend. This divergence is indicative of natural reheating before eruptions, driven either by hotter magma recharging or by crystal settling. It is important to note that this behavior is found in MI hosted in sanidine of the highest magnitude eruption (the Neapolitan Yellow Tuff). The last point is that many MI in the literature are shown as bubble-bearing, but volatile contents of bubble are not taken into account. Thus, more research is needed to test interpretations of preeruptive volatile contents based on MIs.