Insights Into Processes and Timescales of Magma Storage and Ascent From Textural and Geochemical Investigations

Abstract

The mechanisms and timescales of magmatic evolution during storage in crustal reservoirs and ascent in the volcanic conduit exert an important control on both the evolution of precursory phenomena recorded during volcanic crises as well as the style and intensity of the impending eruption. Improving our knowledge on this topic is therefore of paramount importance for better assessment of hazard for active high-risk volcanoes. The densely populated Neapolitan volcanic area (Italy) is one of the places most at risk of volcanic disaster in Europe. To reconstruct the magma plumbing system and its evolution toward critical conditions close to eruption, we employed petrological data on past eruptive products representative of the entire volcanic history. Our results are consistent with the possible existence of a long-term magmatic sill-shaped storage zone beneath the whole Neapolitan volcanic area, with its maximum volume under the Campi Flegrei supervolcano, where the largest eruptions occurred in the last 40 ka. Moreover, slow magma transfer, an open degassing regime, and stasis at a shallow level (ephemeral storage zones) characterize magma ascent during small-scale events, whereas fast magma rise and a continuous closed degassing mechanism drive violent large-scale eruptions. These distinctive dynamics could imply different time-depth patterns of precursory unrest.