Author: Angharad Hills
Last saved by: Tamzin Anderson

Supplementary Material: Sample Descriptions and Analytical Methods
Samples
Sample collection of the juvenile fraction was restricted to pumices from fall deposits of: "Secca d'Ischia" Plinian eruption; three Plinian-subPlinian events of "Russo" explosive eruptions and "Cretaio" subPlinian eruption (Figs. 1, 2 see table below). The juvenile fractions show variable phenocryst content in a glassy matrix. All the selected samples host MIs with a glassy appearance. Major element compositions of MIs do not show any significant depletion or enrichment of elements that would indicate post-entrapment crystallization of the host mineral.
Hydrothermally altered tuffs were sampled (Fig. 1, 2 see table below) on a single vertical outcrops where we were able to sample different tuffs ("Green Tuff", "Frassitelli" and "Pizzone"). The hydrothermal alteration is widespread in all outcrops. 
Fresh and hydrothermally altered xenoliths come from different eruptions (Fig. 1, 2 see table below). These rocks have a nearly holocrystalline texture typical of subvolcanic bodies.

Table. Studied samples in this work
Sample | Rock type | Unit | Sampling area
ISC (AS) 29 | Hydroth.altered tuff | Green Tuff | Rione Bocca
E 4 | Hydroth.altered tuff | Green Tuff | Falanga
ISC05-100 | Hydroth.altered tuff | Green Tuff | Rione Bocca
ISC05-103 | Hydroth.altered tuff | Green Tuff | Falanga
TVE | Hydroth.altered tuff | Green Tuff | Rione Bocca
ISC06-Fras25 | Hydroth.altered tuff | Green Tuff | Monte Cito
ISC05-113 | Hydroth.altered tuff | Pizzone | Rione Bocca
PIZ-2 | Hydroth.altered tuff | Pizzone | Monte Nuovo
RB-1 | Hydroth.altered tuff | Frassitelli | Rione Bocca
ISC06-Fras2 | Hydroth.altered tuff | Frassitelli | Rione Bocca
ISC06-Fras20 | Hydroth.altered tuff | Frassitelli | Rione Bocca
ISC05-112D | Syenitic xenolith | Green Tuff | Falanga
ISC05-13A | Syenitic xenolith | Green Tuff | Forio
ISC10-35 | Syenitic xenolith | Green Tuff | Rione Bocca
RB-2 | Syenitic xenolith | Frassitelli | Rione Bocca
ISC10-17 | Syenitic xenolith | P.ta Imperatore breccia | P.ta Imperatore
ISC06 SGR1LIT | Syenitic xenolith | Secca d'Ischia | Scarrupata di Barano
ISC06-CAS 50 | Syenitic xenolith | Pizzone | Monte Cito
ISC-11 | Syenitic xenolith | Scarrupo di Panza | Citara
ISCP-1 | Juvenile pumices | Russo P1 eruption | Panza
ISCP-2 | Juvenile pumices | Russo P2 eruption | Panza
ISCP-4 | Juvenile pumices | Russo P4 eruption | Panza
ISC AS 5 | Juvenile pumices | Cretaio eruption | Cretaio
ISC AS 64 | Juvenile pumices | Cretaio eruption | Cretaio
ISC07-1 | Juvenile pumices | Secca d'Ischia | Campagnano
ISC07-2 | Juvenile pumices | Secca d'Ischia | Campagnano

Analytical methods
Scanning-Electron-Microscope-Energy-Dispersive-System (SEM-EDS) microanalysis was carried out on individual minerals, on melt inclusions (MIs) in phenocrysts, and on matrix glasses using a Philips XL30 EDAX Genesis. Operating conditions were 20 kV and about 0.1 nA beam current. A raster area of about 100 µm^2 was employed for glass analysis to reduce the light element loss. The analyses were normalized to 100 wt% due to the EDAX software used (Dipartimento di Scienze della Terra of Pisa). Analytical results, errors, reproducibility and detection limits using international standards for SEM-EDS technique are reported in Marianelli & Sbrana (1998).
All MIs selected for analysis had a glassy appearance. The major element compositions of MIs do not show any significant depletion or enrichment of elements that would indicate post-entrapment crystallization of the host mineral.
H_2O content in MIs was determined on double polished inclusions by FT-IR, using a Nicolet Magna-IR560 spectrometer equipped with an MCT detector, a Globar source a KBr beam splitter, coupled with a NicPlan infrared microscope (Dipartimento di Scienze della Terra of Pisa). Spectra were taken with a resolution of 8 cm^-1 and a number of scans variable between 512 and 1024. At least three spectra for different areas were collected for each MI (minimum area of 10 x 10 µm). The concentrations, C, were calculated according to the Beer-Lambert law: C=100xAxM/[exrxd], where A (absorbance) is the peak height of the absorption in dimensionless absorbance units, M the molar mass (g/mol), ethe molar absorptivity (l x mol^-1cm^-1), rthe density (g/cm^3) of glass (estimated using the iterative method of the Church and Johnson (1980) and Gladstone-Dale rules), and d the thickness measured by visual determination under a calibrated microscope, with an error of 2-3 µm depending on the proximity of a given inclusion to the edge of the wafer. The quantitative procedure and the absorption band assignments described in Silver et al. (1990) and Wallace et al. (1999) were followed in this work. The molar absorptivity values chosen were: 62 for the 3570 cm^-1 according to Di Matteo et al. (2004). No carbon peak is observable above the background, indicating the CO_2 is below detection limit (about 50 ppm, depending on MI thickness).
Homogenization experiments on MIs and fluid inclusions (FIs) were carried out on doubly polished wafers of cystals separated from pumice clasts and syenitic xenoliths respectively (Dipartimento di Scienze della Terra of Pisa). Only glassy MIs, with a clear shrinkage bubble and no evidence of heterogeneous trapping (Roedder, 1984), were chosen. For the high-temperature experimental study of MIs, a modified Leitz 1350 heating stage was used. The temperature was measured with a Pt-Pt90Rh10 thermocouple. The accuracy of measurement was around ±10°C, controlled by the melting point of gold and silver. Experiments were performed in a He atmosphere. The rate of heating was varied as a function of the rate of transformation in the inclusions and ranged from 2 to 40°C/min to the point of complete homogenization of MI, i.e., disappearance of bubbles. Pilot runs were carried out in order to define the correct heating/step procedure before the starting of thermometric data collection. Vapor loss can be excluded due to the reproducibility of experiments on the same MI. For the experimental study of FI, a Linkam THMS 600 heating/freezing stage was used. The accuracy of measurements was ± 2°C at 398°C controlled by the melting point of K_2Cr_2O_5, ± 0.1°C at 0°C and ± 0.2°C at –56.6°C controlled by using certified pure water and CO_2-bearing synthetic fluid inclusions (Synthetic Fluid Inclusion Reference Set, Bubbles Inc., USA). The rate of heating and freezing experiments was varied as a function of the rate of transformations in the inclusions and ranged from 2 to 30°C/min.
Silicates were isotopically analysed by laser fluorination, involving total sample reaction with excess ClF_3 using a CO_2 laser as a heat source (T in excess of 1500°C; following Sharp, 1990).  All fluorinations resulted in 100% release of O_2 from the silica lattice. O_2 was converted to CO_2 by reaction with hot graphite, then analysed on-line by a VG PRISM III spectrometer. Reproducibility is better than ±0.3‰ (1s) based on repeat analyses of internal lab standard SES-1 (+9.6‰). For H isotope analysis of phengite, mixed layer chlorite/smectite and mixed layer illite/smectite, water was extracted from several tens of mg of pure mineral, placed in an outgassed Pt crucible, and  heated by radiofrequency induction in an evacuated quartz tube to temperatures in excess of 1500°C. The released water was then reduced to H_2 in a chromium furnace at 800°C (Donnelly et al., 2001). The yield was measured manometrically prior to D/H assay. The gas was subsequently analysed on a VG 602D mass spectrometer. Replicate analyses of water standards (V-SMOW and GISP, and internal standard LT Std) gave a reproducibility around ±2‰. Oxygen and hydrogen isotope data are expressed as d^18O and dD. All stable isotope analyses were carried out at the Scottish Universities Environment Research Centre, East Kilbride.
Bulk rock densities were measured by water displacement method, on specimens of tuffs, syenites and trachytes dried at 60°C, assuming a density value of water of 998 kg/m^3.

References
Church, B.N. & Johnson, W.M. 1980. Calculation of the refractive index of silicate glasses from chemical composition. Geological Society of America Bullettin, 91, 619-625.
Donnelly T., Waldron S., Tait A., Dougans J. & Bearhop S. 2001. Hydrogen isotope analysis of natural abundance and deuterium-enriched waters by reduction over chromium on-line to a dynamic dual inlet isotope-ratio mass spectrometer. Rapid Communications In Mass Spectrometry, 15, 1297-1303.
Marianelli, P. & Sbrana, A. 1998. Risultati di misure standard di minerali e di vetri naturali in microanalisi a dispersione di energia. Atti della Società Toscana di Scienze Naturali, 105, 57-63. In Italian.
Sharp, Z.D. 1990. A laser-based microanalytical method for the in situ determination of oxygen isotope ratios in silicates and oxides. Geochimica et Cosmochimica Acta, 54, 1353-1357.
Silver, L.A., Ihinger, P.D. & Stolper, E.M. 1990. The influence of bulk composition on the speciation of water in silicate glasses. Contribution to Mineralogy and Petrology, 104, 142-162.