CAMPI FLEGREI (ITALY) MAGMA EVOLUTION. COMPARISON OF FONDO RICCIO AND MINOPOLI ERUPTIVE PRODUCTS THROUGH MELT INCLUSION STUDY

Melt inclusions (MI) are a powerful tool for understanding the evolutionary history (crystallization, volatile evolution, mixing, etc.) of magmas. They are also useful to interpret the conditions of primary melt generation and extraction. In particular the volatile content in magmas (e.g. H2O, CO2) is of critical importance in determining the eruptive style and magma evolution, because degassing is usually one of the major phenomena before and during an eruption. In populated and active volcanic areas such as Campi Flegrei (Italy), understanding the role of volatile content in magmas is a necessary requirement to assess volcanic risks. The goal of our project is to define the geochemical parameters that control the internal dynamics of magmatic systems of this active volcanic area. We present a comparison between MI compositions in clinopyroxene and olivine from two eruption (Fondo Riccio and Minopoli) volcanic products which occurred in the Campi Flegrei different in age and in eruptive styles. Fondo Riccio was an explosive eruption (9.5 ka) of strombolian type from an eruptive center sited on the western side of Gauro volcano, at the center of the Campi Flegrei caldera. Minopoli was an explosive magmatic eruption (10.3 ka) with hydromagmatic phases from an eruptive center located along the regional fault system in the northern sector of the Campi Flegrei caldera. Both samples were crushed and olivine and clinopyroxene crystals were hand picked. In these crystals we selected MI that were homogenized and analyzed in order to determine their composition. We present results obtained by Electron Microprobe (EMPA) and Ion Microprobe (SIMS) analyses. Two main differences were observed from the comparison of these two samples. MI from Minopoli samples are less enriched in volatile and Na2O content compared with Fondo Riccio MI. These compositional variations are interpreted as reflecting different hydrothermal processes active before and during the two eruptions.