The contribution of multidisciplinary petrological and geochemical framework (PGF) to assess the influence of plumbing architecture on volcano dynamics and monitoring strategies

Forecasting changes in volcano activity requires a detailed understanding of magma plumbing architecture and dynamics in terms of geometry, distribution and connectivity of the magma bodies and magma properties. This is mandatory to apply effective monitoring strategies and deploy appropriate risk mitigations policies. The PGF's multidisciplinary approach, we have adopted over years on several volcanoes, combines the study and monitoring of petrography and mineral chemistry of erupted products, with the composition of fluids trapped in minerals and the study of gas emissions. This framework permits to constrain magma evolution and dynamics within a volcano plumbing system over a very large range of pressure, temperature and compositions, and on a large range of time scales and frequencies of eruptive events. Here we review the most recent results obtained on two active volcanic systems (Piton de la Fournaise and Mayotte) located in the Indian Ocean, formed in distinct geodynamic settings and with very contrasting eruption rates, volumes, and dynamics, but sharing a common feature: an important lateral shift of the magma ascent paths with respect to the eruptive sites and the coexistence of both evolved (phonolite to trachyte) and mafic (basalts to basanite) melts over a large depth range (from mantle to crust). We show that the most effective monitoring is obtained by focusing on the deepest parts of the plumbing system that allow recognizing and following new magma recharges, melt differentiation and degassing and magma lateral drainage. The occurrence already in the mantle and close to the Moho of variably evolved and degassed melts, besides primitive and volatile rich ones need to be carefully considered, in order to provide a robust interpretation of multidisciplinary monitoring datasets.