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We present experimental phase equilibria carried out on a pantelleritic\udbulk-rock composition with a peralkalinity index [PI¼molar\ud(Na2OþK2O)/Al2O3]¼1·4, which is representative of the most\udenergetic pumice fall eruption of the resurgent post-caldera volcanism\udon Pantelleria island. For the explored conditions (P¼25^\ud150MPa; T¼680^8008C; H2Omelt up to 6 wt %; fO2 NNO,\udwhere NNO is nickel^nickel oxide buffer) clinopyroxene is the liquidus\udphase followed by alkali feldspar and then quartz.The crystallization\udof amphibole is limited to temperatures below 7008C.\udAenigmatite crystallizes near the liquidus for P 100MPa.When\udclinopyroxene is the sole liquidus phase, the coexisting melt is characterized\udby a decrease in peralkalinity index to 1·2, if compared with\udthe starting material, approaching comendite composition. In contrast,\udwhen alkali feldspar joins the liquidus phase assemblage, residual\udmelts become extremely peralkaline (PI¼3·2), with FeO\udcontents in excess of 14 wt %. Comparison of our experiments with\udnatural phase abundances and compositions constrains the depth of\udthe Fastuca pantellerite reservoir to be around 5 1km (or\udP¼120 20MPa) at T¼730 108C, with H2Omelt around\ud4wt %, and fO2 1·5 log unit below NNO. Such conditions correspond\udto the dominant phase assemblage of feldspar, clinopyroxene\udand aenigmatite. Amphibole occurrence requires both higher melt\udwater contents and lower temperatures (up to 6·5 wt % at 6808C),\udand may reflect provenance from a deeper and wetter portion of the\udtapped reservoir. In contrast, quartz is more probably related to crystallization\udduring magma ascent, which explains the lower melt\udwater content of its melt inclusions. Overall, the results confirm\udthat pantellerites may be both water-rich and reduced magmas.\udThese characteristics imply that any coexisting fluid phase in the reservoir\udwill be dominated by water and hydrogen species, the latter\udamounting to a few mole per cent. Magma unrest at Pantelleria\udmay thus be heralded by emissions of hydrous and reduced gases\ud(i.e. CO2-poor and H2-rich), if the present-day reservoir is felsic in\udcomposition

Phase Equilibrium Constraints on Pre-eruptive Conditions of Recent Felsic Explosive Volcanism at Pantelleria Island, Italy