We estimated crystallization temperatures and magma water contents using a clinopyroxene-liquid thermometer (24) and a K-feldspar–liquid hygrometer (25) specifically calibrated to alkaline compositions akin to the Campi Flegrei magmas. We compared crystal cores with bulk rock/clinopyroxene-hosted melt inclusion compositions, which approximate the composition of the melt during the early stages of crystallization, and crystal rims with matrix glasses, which closely resemble the composition of residual melt during the final stages of crystal growth (53). For the thermometric calculations, we used water contents of 3 wt % (mafic magmas, DI ≤ 73), 4 wt % (intermediate magmas, DI = 74 to 90), and 4.5 wt % (evolved magmas, DI ≥ 91). Notably, the estimated temperatures obtained by varying the water content by 2 wt % are included within the error of the method [±20°C; (24)]. A K-feldspar crystallization temperature of 850°C was used for the hygrometric calculation based on rhyolite-MELTS thermodynamic simulations (fig. S6). An error of ±0.7 wt % is normally associated with the magma water content estimated using this method (25). The equilibrium conditions between mineral and melt compositions were determined by means of test for equilibrium based on clinopyroxene-melt and K-feldspar–melt exchange reactions (25, 54). Only equilibrium pairs were used for calculating temperatures and magma water contents. Note that a pressure input is required to account for the equilibrium between clinopyroxene and melt. We used 300 MPa for the most mafic magmas of Minopoli 1 and 2 (55, 56), 250 MPa for the pre-CI and CI (57), and 200 MPa for all the other eruptions based on the most recent geophysical data (58), which identify the current melt storage zone at a depth of ~7.5 km, corresponding to ~200 MPa, assuming a density of about 2700 kg/m3.

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