Understanding magma evolution at Campi Flegrei (Campania, Italy) volcanic complex using melt inclusions and phase equilibria

The magmatic evolution of two eruptive episodes at Campi Flegrei (Italy) has been investigated using phase equilibria modeling (MELTS) and data from melt inclusions (MIs) in phenocrysts from the Fondo Riccio and Minopoli 1 eruptions. Assuming that isobaric fractional crystallization of a mantle-derived parental magma is the dominant petrogenetic process, major element evolution and corresponding changes in the physical and thermodynamic properties of the magma bodies from which Fondo Riccio and Minopoli1 magmas were erupted can be tracked. Fondo Riccio parental magma was trachyandesitic, approximated by the composition of FR-C1-O2-M1, which evolved mainly through fractional crystallization at low pressure (P a parts per thousand aEuro parts per thousand 0.15 GPa, a parts per thousand 7 km depth), along the QFM, QFM + 1 oxygen buffer with an initial dissolved H2O content of 3 wt%. Minopoli1 parental magma was trachyandesitic, approximated by the chemistry of Mi1-C1-O5-M1, evolved through fractional crystallization at P a parts per thousand aEuro parts per thousand 0.3 GPa (a parts per thousand 12 km depth), with oxygen fugacity along QFM + 1buffer and initial H2O content of aEuro parts per thousand 2 wt%. The relationship between melt fraction and T reveals for Fondo Riccio the presence of a pseudo-invariant temperature at which the physical properties of melt change abruptly. The net effect of these changes is to drive the system towards dynamic instability, which it is suggested to be the trigger mechanism for the eruptions.