Exploring the pre-eruptive magmatic processes through melt inclusions: the case study of the Campi Flegrei Caldera.

The Campi Flegrei caldera (CFc), one of the highest risk volcanic areas on Earth and the most dangerous volcano in Europe, originated from two large-scale caldera-forming eruptions occurred 40 and and 15 ka. Since 2005, it has been experiencing a new phase of unrest manifested by intensified ground uplift, seismicity and hydrothermal activity. The aim of this study is to investigate the magma volatile content and composition in pre-eruptive conditions through the study of melt inclusions in phenocrysts of pyroclastic rocks erupted in the last 15 ka. Study samples were collected from different deposits of several representative eruptions (Baia, Averno 2, Fondo Riccio, Minopoli, Astroni, Agnano-Monte Spina, Montagna Spaccata, St. Teresa, Nisida). Sixtyfive melt inclusions within olivine, clinopyroxene and alkali feldspar phenocrysts (perfectly glassy, regular shape, 20-30 µm in size, one or two fluid bubbles) representative of the studied eruptions were selected by microscope analysis. Image analyses performed on the inclusions allowed us to determine the ratio between the volume of the fluid bubble and glass in each inclusion. A comprehensive geochemical characterization of the melt inclusions has been systematically conducted using a combination of Raman spectroscopy, electron microprobe, laser ablation-inductively coupled mass spectroscopy, and nano secondary ion mass spectrometry. Such a complete dataset lays the foundation for a thorough investigation of the architecture and dynamics of the shallow CFc magma storage system, as well as for formulating pre-eruptive scenarios in the CFc active volcanic area.