Juvenile clasts representative of 23 different eruptions were sampled at Campi Flegrei caldera and in more distal outcrops (Fig. 1 and Supplementary Materials). All samples were analyzed for bulk rock composition by x-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICPMS) at Eidgenössische Technische Hochschule (ETH) Zürich. Fused whole-rock XRF beads (1:5 lithium tetraborate dilution) were analyzed using a PANalytical Axios wavelength-dispersive XRF spectrometer following a 2-hour devolatilization period at 950°C. Loss on ignition was calculated as the difference between the weight of the original sample (~1.6 g) and that of the sample after devolatilization. Subsequently, XRF pills were analyzed using a 193-nm Lambda Physik Excimer ArF laser coupled to a PerkinElmer ELAN 6100 ICPMS system. Analyses were calibrated and drift corrected using the NIST 610 synthetic glass standard and were blank corrected using a lithium tetraborate blank. Spot sizes were 90 μm (lithium tetraborate blank) and 40 μm (sample), and an average of three points was taken per sample. A subset of samples representative of all the studied eruptions was selected for glass, mineral chemistry, and crystallinity analyses. Mineral phases and matrix glass were analyzed for major elements by electron probe microanalysis (EPMA) at ETH Zürich and Istituto Nazionale di Geofisica e Vulcanologia (INGV) Rome. The operating conditions were as follows: 15-kV acceleration voltage, counting times of 20 s on the peaks and 10 s on the backgrounds, and 20 nA (clinopyroxene, feldspars, and oxides) or 15 nA (biotite and glass) beam current. To minimize alkali migration, K and Na were always measured first, and a defocused beam (20 μm) was used for feldspar, biotite, and glass analyses. Analyses were typically reproducible to <5% for all major and minor elements. Trace element compositions of mineral phases and matrix glass were measured by laser ablation ICPMS (LA-ICPMS) at ETH Zürich using a 193-nm ArF Excimer laser from Resonetics coupled to a Thermo Element XR ICPMS. A spot size of 43 μm was used for mineral analyses and reduced to 20 μm for glass analyses; output energy of the laser beam was typically ~3.5 J/cm2. The MATLAB-based SILLS software (52) was used for data reduction using NIST 612 and NIST 610 external standards. The U.S. Geological Survey reference glass GSD-1G was used as a secondary standard to monitor the accuracy of the instrument. For each data point, appropriate major element concentrations from EPMA analyses were used as internal standards. Long-term laboratory reproducibility of homogeneous glass standards indicated precision significantly better than 5% for elements, whose concentration was much greater (i.e., 2×) than the detection limit. Relative crystallinity was estimated by means of x-ray powder diffraction at ETH Zürich using an AXS D8 Advance diffractometer equipped with a Lynxeye superspeed detector. Powdered samples were analyzed using CuKα radiation generated at 40 kV and 40 mA. Scans were run at 5° to 90° 2θ using a 0.02° step size and 1-s dwell time. Diffractograms were processed using the method described in (27). Both bulk rock and groundmass crystallinities were estimated for samples that showed incipient groundmass crystallization. In these cases, the relative crystallinity was calculated by subtraction. The full datasets of bulk rock, matrix glass, mineral chemistry, and crystallinity calculations are reported in data file S1.

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