Geochemistry of melt inclusions from the Fondo Riccio and Minopoli 1 eruptions at Campi Flegrei (Italy)

Campi Flegrei is a large volcanic complex (similar to 150 km(2)) located west of the city of Naples, Italy. The area has been the site of volcanic activity for more than 60,000 years and represents a potential volcanic hazard owing to the large local population. In this study, the geochemistry of the magma associated with two different eruptions at Campi Flegrei has been characterized, with the aim to identify geochemical trends that may help to predict the style and nature of future eruptions. Two eruptions of different age and eruptive style have been selected for study, Fondo Riccio (9.5 ka) and Minopoli 1 (11.1 ka). A scoria (CF-FR-C1) and a bomb (CF-FR-C2) were collected from the Fondo Riccio eruption, and two scoria samples were collected from the Minopoli 1 (CF-Mil-C1 and C2) eruptive products. The pre-eruptive volatile content of magma plays an important role in the style of eruption. The original volatile content of magma can be assessed from studies of melt inclusion (MI) contained in phenocrysts. MI data show two trends for Fondo Riccio - one from latite to trachyte for MI in Fe-rich diopside (C1) and another from trachybasalt to shoshonite for MI in Mg-rich diopside (C2) and for MI in olivine (C1). Minopoli 1 MI data show two different compositions - basaltic for MI in clinopyroxene (MiI-C1) and trachybasalt for MI in olivine (MiI-C1) and clinopyroxene (MiI-C2). Major and trace element data for Fondo Riccio MI show a compositional gap between Mg# 78 and 83, whereas Minopoli 1 MI have Mg# between 85 and 89 and show no compositional gap. Clinopyroxene compositions fall in the diopside-salite field for Fondo Riccio and in the diopside field for Minopoli 1. Fondo Riccio olivine compositions show a wider range (Fo(84.60) to Fo(86.77)), compared to Minopoli 1 olivine (Fo(77) to Fo(78.5)). Analyses of reheated MI suggest trends in MI volatile contents that correlate with SiO2 concentration. In particular, more evolved MI show higher Cl and lower S compared to less evolved MI. The H2O content of MI from the two eruptions overlap but suggest that the Fondo Riccio magma may have been more water-rich. The higher H2O content of the Fondo Riccio magma (2.5 to 6.9 wt.%) compared to Minopoli 1 (1-3.5 wt.%) is consistent with the more explosive nature of Fondo Riccio eruption compared to Minopoli 1.