Magma Degassing Models and Decarbonation Processes Affecting Hydrothermal Calcite

The Campi Flegrei caldera represents an ideal natural laboratory for investigating volcanic carbon dynamics, offering a unique opportunity to explore the interplay between magmatic and hydrothermal processes. This work synthesizes recent studies to provide a comprehensive overview of key processes such as magmatic degassing, hydrothermal decarbonation, and carbon sequestration via calcite precipitation. These phenomena not only shape the geochemical signals crucial for volcanic risk assessment but also drive significant chemical and physical transformations within the caldera fill deposits. Specifically, the precipitation of hydrothermal calcite occurs at the expense of the alteration of caldera-filling tuffs, leading to changes in their porosity and permeability. This, in turn, modifies the mechanical properties of these rocks, with critical implications for their deformation and fracturing behaviour under stress. Such changes play a fundamental role in influencing the mechanical stability of the caldera system and the evolution of hydrothermal reservoirs, with direct consequences for volcanic hazard scenarios. Moreover, the findings underscore the complex interplay between magmatic and non-magmatic contributions to CO2 emissions. Hydrothermal calcite emerges as a dual agent in this context: functioning as a carbon sink during quiescent phases and as a potential source during periods of hydrothermal perturbation or reactivation. These dual roles highlight the dynamic nature of carbon cycling within the caldera and the need for integrative approaches to monitor and model these processes. By advancing the understanding of volcanic carbon cycling, this work provides a framework for investigating similar systems worldwide. Methodologies and conceptual models developed here could serve as benchmarks for studying other calderas, enhancing global capabilities in volcanic monitoring and risk mitigation.