Mineral chemistry profile: a valuable approach to unravel magma mixing processes in the recent volcanic activity of Stromboli, Italy

A mineral chemistry study including compositional zoning profiles on clinopyroxene and plagioclase has been performed on pyroclastic deposits of recent Stromboli (with an age of about 2- 3 ka), erupted just before the setting of the typical present-day Strombolian activity (Post-Pizzo series). The mineral chemistry characterisation of samples from the bottom and top of the Post-Pizzo series has revealed a complex magmatic history recorded by mineral phase compositional variations. These data suggest that the initial phase of the eruptive period of Post-Pizzo series was characterised by repeated arrival of mafic magmas emphasized by several changes in the crystal compositions. After the magma hybridization, the system nearly recovered its initial composition by associated continuous fractional crystallisation, thus establishing a nearly steady-state dynamics of the magma system. The arrivals of mafic magma batches became more important during the late Post-Pizzo eruptive period, leading in the final stage to a more mafic magma composition, similar to that of the basaltic products erupted by the present-day activity. This plumbing system behaviour reminds the dynamics driving the pre-eruptive processes responsible of the present-day Strombolian activity. Accordingly, the Post-Pizzo series seems to represent the period during which the magmatic conditions for the present-day activity were developed. The micro-analytical approach using zoning profiles can be considered a powerful tool in revealing magma mixing processes and in helping to clarify the dynamics of magmatic systems.