High pressure experiments on kinetic and rheological properties of primitive alkaline magmas. Constraints on deep magmatic processes at the Campi Flegrei volcanic district

Defining the timescales of magma storage and ascent beneath active volcanoes is a fundamental tool in volcanological investigation of the last decade to constrain pre-eruptive magmatic processes and magma chamber dynamics, since it is able to provide the basis for volcanic hazard assessment. This Ph.D. thesis focuses on the investigation of the deep portion of the Campi Flegrei Volcanic District plumbing system (crustal-mantle boundary; ~25 km of depth), in correspondence of which the presence of a possible crystallization zone has been hypothesized on the basis of melt inclusion studies (Moretti et al., 2013; Mormone et al., 2011), seismic data interpretations (Chiarabba et al., 2008; Di Stefano et al., 1999; Piochi et al., 2005), gravimetric and petrological modelling (Fedi et al., 2018) and experimental data (Perinelli et al., 2019). The Campi Flegrei Volcanic District, which includes the Campi Flegrei and the islands of Ischia and Procida, represents one of the most active volcanic areas in the Mediterranean region and one of the most dangerous volcanic complexes on Earth owing to the intense urbanization of the area. Many petrological, geochemical and geophysical surveys were carried out in the Campania Active Volcanic Area that have helped to define the main architecture and the development of the sub-volcanic system. Nevertheless, the dynamic processes that operate during the earliest, deepest differentiation steps of primitive magmas that fed all Campi Flegrei eruptions are yet poorly constrained. The knowledge of the timescales of magma formation, storage and ascent beneath active volcanoes is the key to constrain pre-eruptive magmatic processes and magma chamber dynamics, providing the basis for volcanic hazard assessment (e.g., Petrone et al., 2016). Estimates of these timescales and knowledge of magmatic processes can be obtained by several methods (Costa et al., 2020, and reference therein), among which (i) the investigation of kinetics of crystal nucleation, growth and dissolution, (ii) rheological properties and (iii) partitioning of trace elements between crystals and melts. In this thesis, the investigation of the kinetic and rheological properties of a K-basaltic magma at Moho depth, together with the partitioning of trace elements between crystal and melts, has allowed to fill some gaps relative to the knowledge of the deep portion of the Campi Flegrei Volcanic District plumbing system, providing magma residence time and ascent timescales, and models for deep magmatic differentiation processes.