• Baia
• Campi Flegrei
• compositional study
• Fondi di Baia
• magmatic systems
• melt inclusions
• mingling
• mixing
• shallow magma batches
• tephriphonolite
• trachyte

The Baia-Fondi di Baia eruption is a small-scale eruptive event which occurred in the western part of the Campi Flegrei caldera (CFc). The CFc is an active volcanic system situated in the western part of the densely populated area of Naples Bay, Italy. In its past it has been characterised by various epochs of volcanic activity. The eruptions of the Campanian Ignimbrite (CI, 39 ka BP) and of the Neapolitan Yellow Tuff (NYT, 15 ka BP) have determined the Campi Flegrei’s present morphology and its dominant, partly submerged, nested caldera structure. In the time span following the NYT eruption, about 70 known eruptive events have taken place within the caldera; they can be mainly subdivided in 3 eruptive epochs, separated by periods of quiescence of variable duration: Epoch 1 (15.0–9.5 ka), Epoch 2 (8.6–8.2 ka), and Epoch 3 (4.8–3.7 ka). The most recent eruption is represented by the event of Monte Nuovo at 1538 AD.
The Baia-Fondi di Baia eruption marks the onset of Epoch 2; it occurred after a 1000 years-long quiescence and is dated back to 9525–9696 cal BP (Di Vito et al., 1999; Smith et al., 2011). The aim of this study is the understanding of the magmatic system and the magmatic processes that took place prior to the eruption and which likely led to the reactivation of the Campi Flegrei plumbing system after a period of quiescence. The reconstruction is based on field investigations, compositional analyses of the collected samples and further investigations on the geochemical and mineralogical characteristics of the deposits.
The obtained results reveal that the Baia-Fondi di Baia eruption can be considered as a complex series of events which can be grouped in two main eruptive sequences (Baia and Fondi di Baia). Two magmatic systems have been identified at a pressure range between ~20 and 170 MPa. They involve a shallow, isolated reservoir of trachytic magma and a more complex, interconnected system at greater depths with compositions ranging from phonolite to trachyte. Both systems were tapped during the Baia as well as during the Fondi di Baia event, though variations in relative proportions of the two involved magmas are evident between the two eruptive sequences.